spsg sn76489 user manual v1.
Contents
1. 25 SPECIAL TIMERS amp AY EG 27 TABLES 35 NOISE LFSR CHANNEL 37 PCM SAMPLES 39 PRESETS IMPORT EXPORT 41 MIDI AUTOMATION 42 HARDWARE 44 HIDDEN SECRETS 45 LINKS 48 DISCLAIMER amp LICENCE AGREEMENT 50 INTRODUCT2. The nature of this noise is very 8 bit sounding and immediately links you to some magic era The LFSR can also be put in a closed loop when in PERIODIC mode the output bit will also be the input bit resulting in a 1 16 pulse waveform witch is also 4 octaves down from the played frequency This allowed for crunchy bass lines that the tone channels cannot reach at NTSC or PAL CLOCK Each time the NOISE register is rewritten the LFSR is reset This means that you can have better randomness in the noise if you play drums with a FIXED frequency as you will only write to the volume register Note that when you start the VST some cycles will pass through and the LFSR state displayed will be different than 0x8000 but the initial state is really 0x8000 NOISE channel was often used for drums percussion or explosion type effects It also can be used in conjunction with a tone channel for example to fatten a percussive sound or provide a transient part SLOTS There are 8 MEMORY SLOTS available these are memory storage for most of the LFSR panel settings you can switch between them via automation at any time for complex evolving sequence and even control them with TABLES see TABLES You can also COPY a MEMORY SLOT to another via the COPY FROM button SPSG VST provides some circuit bending options over the LFSR configuration if you want to expand the palette of noise types You can change the NOISE TYPE between WHITE or PERIODIC witch ar
3. X1 will basically cycles the entered notes X2 will push it one octave X2 two Octaves and so on MIDI DIRECTION Will set the direction of the arpeggio UP DOWN UPDOWN amp also RANDOM Set it to OFF will disable the MIDI ARPEGGIATOR SPECIAL TIMERS amp AY EG This panel features some complex modulation routines using software TIMER interrupts the AY3 8910 emulated envelope generator or both Any numbered parameters can also be typed directly via keyboard HINT You can randomize custom timer waveforms by Left clicking CTRL MAJ THE BUTTONS ON THE LEFT WILL ACTIVATE THE DIFFERENT MODULATORS AVAILABLE This important to understand that the TIMER interrupt routine and the HARDWARE envelope can generate both very low frequencies while the 10 bit frequency counter of the natural TONE channel is more limited in regard of the MASTER CLOCK frequency The result is that when you use TIMER or HARDWARE to modulate the TONE you will hear that the TONE frequency will stick to its lowest limit according to the chip MASTER CLOCK while the TIMER amp the HARDWARE still outputs the played frequency You can minimize this effect simply by lowering the MASTER CLOCK lowest possible clock of 1000000 Hz will have a limit of 30 52 Hz Z80 Timer The SN76489 can produce 16 discrete levels internally set from 15 MAX attenuation to 0 FULL VOLUME If you use a TIMER Interrupt to write a routine to the volume register at audio rate
4. however with particular settings the output of not rescaled data sample can act as a transient enhancer of some sort PULSE WIDHT MODULATION PWM This method is basically a 1 bit MAX volume or MIN volume conversion of the sample data and will therefore be louder than PCM method and really raw You can choose between the playback modes via the MODE button PCM is quieter than PWM but also more precise PUSLE CODE MODULATION PCM The volume setting is used as a 4 bit DAC All three tone channels can be used together to get maximum volume if needed by selecting PLAY ON 3 CHANNELS PRESETS IMPORT EXPORT FXP amp FXB SPSG can load and import its own format presets amp banks All memory SLOTS from the current preset are also saved with the patch All MIDI LEARNED amp ASSIGNED parameters will also be saved with the patch Simply name the preset and right click the PATCH MENU to save either 1 preset instrument or the whole bank you can also copy the current patch to another location MIDI AUTOMATION MIDI LEARN Almost all of the SPSG parameters can be automated via midi learn or DAW automation allowing great control over the sound Be careful when used in conjunction with TABLES See SPECIAL Simply right click on a button knob or slider to assign external MIDI Control or use DAW automation Almost all type of MIDI message can be assigned or MIDI learned MIDI OUT All assigned mid
5. ENVELOPE GENERATOR Optional AY3 8910 emulated Envelope Generator Buzzers Sync Buzz A feature that was only available on the AY and YM2149 chip ZX spectrum MSX Atari ST Z80 SOFTWARE TIMER Z80 Timer pulse width modulation SID Sound or custom waveforms can also synced the AY3 8910 Hardware Envelope Generator for sync type effect NOISE CHANNEL CIRCUIT BENDING the LFSR generator is tweak able in real time tapped bits mask and feedback bit from the original fixed 16 bit configuration of the Sega Master System Genesis to anything in between which basically gives you the ability to reach some different sound chips type of noise or mess it up in a unique way all of that in real time MIDI OUT FOR AMPLITUDE amp PITCH LOAD amp SAVE FULL PATCH amp BANKS in FXB FXP CONTROLS A REAL SN76489 CHIP or MASTER SYSTEM MEGADRIVE HARDWARE VIA MIDI For Master system or Megadrive Needed Little Scale SMSN GENMDM Midi Device An ATMEGA MIDI controlled SN76489 device can be easily built if needed open source code is available on request CONTROL PANELS Overview SPSG GUI INTERFACE stores the different parameters on different panels The main sliders TONE NOISE amp PCM sets the global volume multiplier for each channel SYNC is the master envelope clock in BPM that is affected to an envelope if set see ENVELOPES LFO set the vibrato speed and PMS the amount of pitch modulation only affect TONE channel The SETTINGS button opens th
6. Once a new key is played the TABLE will restart from STEP1 and will usually stops where it is if you release a key unless a RELEASE MODE is set see GATE RELEASE in the AMP or PITCH section The Step table time will be defined by the defined number of steps of an envelope except for the SPECIAL amp LFSR table that featured their own separated clock source That means that if a volume envelope has for example 16 steps the time of a step in the table before changing the memory slots will take 16 steps The Slot Sequencer Cartridge displays the current playing memory SLOTS while the sequence cycles through While tables can reach complicated patterns they also might mess with the registers sometimes real chips have some non linearity and unpredictability that I try to slightly inject in the SPSG VST NOISE LFSR CHANNEL SPSG provide an independent control over the noise channel it features the same type of volume amp pitch envelope as the tone channel but adds a different control over the special capabilities of noise source The envelopes colors are lighter than the TONE ones for easy distinction The LFSR state can be seen in real time and can also be configured in a completely different way than on the SEGA SN76489 VDP integrated chip Frequency Control The SN76489 differed from other types of PSG via the possibility to control the NOISE frequency precisely FRQ CONTROL Will switch between to 2 frequenc
7. can choose between 4 built in settings NTSC PAL 1MHz or 4MHz Of course you can set anything in between and every calculation of the ship will accurately depend on that clock You can also choose the output filtering of the SN76489 between Sega Master System console Sega Genesis Megadrive and the direct unfiltered output of the chip This is also here that you can set the Pitch Bend Range and the mono Portamento affect for TONE amp NOISE channels You can also choose if you play only one TONE channel Mono or the 3 at the time which will share the same envelopes and settings POLY The Last part will set the configuration for MIDI OUT data that SPSG will be sending see MIDI AUTOMATION Settings Parameters MASTER CLOCK Select NTSC PAL 1Mhz or 4Mhz You can also type in any value between 1 MHz and 4 MHz 1000000 and 4000000 VOICE CONTROL Choose the MIDI channel that the voice will respond to Note that you can assign the same MIDI channel to many sources for example to control noise amp tone at the same time The configuration is saved with patches TONE POLY STATE Switch between MONO plays only one tone channel or POLY to play the 3 tone channels at the time with the same envelopes and settings ENVELOPE RETRIGGER When ON each new key will retrigger envelopes from the beginning sometimes it is preferable to retrigger only on non legato notes so this can be OFF MONO CONTROL PT
8. is the Portamento setting and PBR is the pitch bend range in semitones SN76489 FILTERING Choose between SMS GENESIS or direct non buffered unfiltered chip output NOISE LFSR STATE Is just a reminder of the actual state of the LFSR noise channel MIDI OUT ENABLE the MIDI OUT if needed or leave it to DISABLED see MIDI AUTOMATION AMP GENERATOR Simply draw the envelope with the mouse click on a particular step to select it Any numbered parameters can also be typed directly via keyboard HINT You can randomize any envelope by Left clicking CTRL MAJ THIS SWITCH WILL ACTIVATE OR DEACTIVATE THE ENVELOPE GENERATOR Volume Envelopes AMP ENVELOPE GENERATOR FOR THE TONE amp NOISE CHANNEL AS THE SAME BEHAVIOR The SN76489 can produce 16 discrete levels internally set from 15 MAX attenuation to 0 FULL VOLUME The sound starts when the key is depressed a process called key on The sound will then passes to each stages steps of the envelope and sustain on the last step The more the steps and speed the less stepper the resulting envelope will be SPSG can reach near 300 Hz speed ticks per second however keep in mind that most of the sound drivers used in past games rarely outputs more than 60 Hz even if the sound chip itself can These are the main parameters of an AMP envelope STEPS Is the number of steps that will be played can be anything between 1 to 64 steps The number
9. will then output a 1 16 duty cycle pulse wave which is 4 octaves down compared to the tone channels even if the same frequency is set This is mainly because it takes 16 more time for the output bit to be toggled than on a normal tone channel resulting in the actual frequency being FRQ 16 The frequency resolution of higher notes being limited this also results in a slight detuning between periodic and tone output frequency although they have the same frequency setting On the SEGA VDP integrated version of the chip It means that it will take 57337 different 16 bit patterns before the LFSR comes back to its initial 0x8000 1000000000000000 state In addition several advanced techniques can be used to produce interesting modulation for example you can use the Z80 processor of the Sega Master System to write MAX volume MIN volume to the volume register of a channel if you do this at audio rate this will produce another square wave If you set this modulation at nearly the same frequency than the actual tone this will produce a change in time of the pulse width and the more detuned the more the beating effect you can also output more complex waveforms this way PCM samples can also be played in a limited way on the volume register by setting the frequency to 0x000 to produce a DC modulated by the sample data You can either use PCM or PWM method Mixing the two without setting all 0 frequencies can lead to interesting crea
10. DI can be selected by clicking on the red centered screen display Any numbered parameters can also be typed directly via keyboard THIS SWITCH WILL ACTIVATE OR DEACTIVATE THE ARPEGGIATOR Arp Play Modes SPSG can reach near 300 Hz speed ticks per second however keep in mind that most of the sound drivers used in past games rarely outputs more than 60 Hz even if the sound chip itself can The arpeggiator can behave in two distinct ways depending on the setting PROGRAM MODE In PROGRAM mode you set the desired 3 notes via the 3 red sliders or by selecting the value directly the arpeggiator will always begin on NOTE 1 MIDI MODE In MIDI mode the arpeggiator will process the notes that you play according to the MIDI MODE OCTAVE amp MIDI DIRECTION settings regardless of the STEPS setting This mode is more adapted to complex live playing and produces great results in term of nonlinear arpeggios These are the main parameters of the ARPEGGIATOR STEPS Is the number of steps that will be played can be anything between 1 to 64 steps The number of steps played can be automated in real time As the arpeggiator in PROGRAM mode as only 3 steps the STEPS parameter is used for the amount of time you want it to be on Depending on the STEPS setting the last note will not necessary be the First or the Last An easy way to calculate for the last step being the first is that the STEPS must be equal to a multiple of 3 and ad
11. ION My name is Aly James French steam funky musician composer and creator of strange musical DIY devices and software Based on the relatively good success of my Sega Megadrive Genesis VSTi FMDrive I was planning to make an entirely separate VST dedicating to the second Sound Chip aka PSG SN76489 also known as DCSG The SN76489 was also the main sound chip of the Sega Master System console and the second sound chip of the Sega Megadrive Genesis It was originally integrated in my FMDrive VST but I have decided to give it its own dedicated host with lots of features and controls A very similar chip was also the AY3 8910 ZX SPECTRUM MSX that lacks a real independent frequency control of the noise channel but adds a hardware envelope that can be used to produce waveforms instead It is nice to notice that his looping envelope feature will also end in the YM2612 as the SSG envelope part The Japanese Master System also featured a limited FM module via the YM2413 chip This is not emulated in SPSG VST because we have YM2612 FMDrive VST that can do way better on the FM side ________________________________________________________________________________ Like said previously I am not very used to tracker music making or MML programming which is why I needed an SN76489 VST Instrument I also needed a way to control the real hardware via MIDI I learn a lot from documentations and hardware testing and also from all the nice peo
12. SUPER PSG VST SN76489 SMS www alyjameslab com USER MANUAL 1 0 BY Aly James 2013 2014 ALYJAMESLAB TABLE OF CONTENTS SUPER PSG VST 1 INTRODUCTION 3 INSTALLATION 6 CONTROL PANELS 9 THE SN76489 PSG CHIP 11 MAIN CONTROLS 15 SETTINGS 17 AMP GENERATOR 19 PITCH GENERATOR 22 ARPEGGIATOR
13. Will usually be set to KEY that means that the TONE channel frequency is controlled by the notes you play However if you want to only hear the Timer waveform or the Hardware waveform without Tone modulation you have to force the TONE frequency to 0 The setting ZERO will then set the Tone frequency to 0 disabling the TONE output Note that this can also be used to only modulate DC with the AMP envelope generator HARD SYNC This is the SYNC BUZZERS type effect when on the TIMER will be also used to restart the HARDWARE envelope producing a sync type effect Great effect is applicable if you set the TIMER frequency lower than the HARWARE and from there change the hardware frequency to hear the effect the type of waveform will also influence the final output HARD RETRIG When ON this will rewrite the hardware register with the current selected envelope doing this will restart the envelope and the phase Note that the TIMER phase is automatically restarted Useful to synchronize waveforms phase movements or to simply add a little punch to the sound FREQ RATIO Will calculate the frequency needed to synchronize the TONE frequency with the TIMER amp HARDWARE as explain previously From 1 1 that tries to apply the PSG frequency to the hardware frequency with precision loss to 8 1 that will produce a more similar pitch and anything in between You can experiment with this as it will produce different
14. You may not sublicense rent lease convey distribute copy modify translate convert to another programming language decompile or disassemble the Software for any purpose You may only redistribute the Software for promotion purpose with Aly James prior written permission Where redistribution is authorized in writing by the Author SPSG must be redistributed in its original archive format and must not be modified in any way All such authorized redistribution must be accompanied by clear messages stating the origin of the software as an Aly James Lab product this license a link to the Website alyjameslab com The user ID is hard coded into the GUI and each version of the software is unique By Using the Software you are agreeing to this disclaimer and license VST is a trademark of Steinberg Media Technologies GmbH SPSG does not emulate a Sega Master System console but the sound chip that was inside witch basic function is reproduced here but enhanced a lot It is not a straight binary copy and the system is enhanced amp totally new Secondly the use of Sega name and logo type font is use strictly here for the legitimate purpose of comparison and tribute to this great console and it does not in any way imply SEGA s permission or endorsement of the SPSG product 2013 2014 ALYJAMESLAB
15. an randomize any envelope by Left clicking CTRL MAJ THIS SWITCH WILL ACTIVATE OR DEACTIVATE THE ENVELOPE GENERATOR Pitch Envelopes PITCH ENVELOPE GENERATOR FOR THE TONE amp NOISE CHANNEL AS THE SAME BEHAVIOR REMINDER The SN76489 can produce 1024 discrete pitch The sound starts when the key is depressed a process called key on The sound will then passes to each stages steps of the envelope and sustain on the last step The more the steps and speed the less stepper the resulting envelope will be SPSG can reach near 300 Hz speed ticks per second however keep in mind that most of the sound drivers used in past games rarely outputs more than 60 Hz even if the sound chip itself can These are the main parameters of the PITCH envelope STEPS Is the number of steps that will be played can be anything between 1 to 64 steps The number of steps played can be automated in real time and will not discard the steps previously set if you reduce the number dynamically SPEED Is a clock speed multiplier it will multiply the PITCH CLOCK by the amount ex CLOCK 120 SPEED 2 will play each step at 120 2 240 BPM SLOTS There are 8 MEMORY SLOTS available these are memory storage for the 64 envelope steps levels you can switch between them via automation at any time for complex envelopes and even sequence them with TABLES see TABLES You can also COPY a MEMORY SLOT to another via the COPY FROM bu
16. d 1 SPEED Is a clock speed multiplier it will multiply the ARP CLOCK by the amount ex CLOCK 120 SPEED 2 will play each step at 120 2 240 BPM SLOTS There are 8 MEMORY SLOTS available these are memory storage for the 3 ARP notes you can switch between them via automation at any time for complex evolving arpeggios and even sequence them with TABLES see TABLES You can also COPY a MEMORY SLOT to another via the COPY FROM button CLOCK This is the main CLOCK of the arpeggiator in BPM it is the principal parameter to calculate the arpeggiator step final speed If you click on the SYNC button the CLOCK value will turn green and will be controlled by the main SYNC value SYNC slider on the main panel LOOP Is the number of steps that has to be played before activating the LOOP mode For example let s say we have set a 15 steps arpeggiator then if you set the LOOP parameter to 32 the result will be gt gt PLAY the 15 STEPS gt gt WAIT for 16 STEPS gt gt PLAY AGAIN from STEP 1 and so on As the loop mode is a power of 2 some STEPS settings can ends on a different notes on each new pass this can be used creatively Basically set it to 2 to LOOP endlessly DELAY Will wait x DELAY amount of steps before triggering the arpeggiator this is very useful when you don t want to apply the arpeggiator immediately after a key on These are the main parameters of the MIDI MODE MIDI MODE OCTAVE
17. e envelope to only 1 step and activate RSTEP Note that the last step has to be reached before applying If a release step is activated the display will highlight a full bar for the last step SYNC When this button is ON red the CLOCK BPM value will turn green and will be controlled by the main SYNC value SYNC slider on the main panel It is useful to sync AMP PITCH etc when in need to control the main speed with only one main SYNC slider GATE RELEASE When in GATE mode the sound will immediately stops and be set to minimum volume when a key is released regardless of what value the current step volume was on This is the most common setting When in RELEASE mode the sound will play all the steps in the envelope even if a key is released except if it encounters a 0 volume STEP in this case it will stops at the first step that as a 0 volume value Be careful with this release setting as it will maintain a voice awake an can produce a sound when you load a project this should only be used to record and set back to GATE mode before saving for safer usage NORMAL REVERSE Only if the LOOP parameter is activated a REVERSE setting will play the envelope from END STEP to START STEP once the last step is reached PITCH GENERATOR Simply draw the envelope with the mouse click on a particular step to select it draw or single Any numbered parameters can also be typed directly via keyboard HINT You c
18. e lowest possible frequency for a fixed clock can be calculated this way The frequency range VS master clock speed DCSG CLOCK Hz DCSG FREQUENCY RANGE Hz 4000000 3579545 NTSC 3546893 PAL 2000000 1000000 122 070312 125000 109 239044 111860 78125 108 242584 110840 40625 61 0351562 62500 30 517578 31250 The noise channel can be either WHITE noise or PERIODIC as for the tone channels the output bit is toggled between 0 and 1 but this time it is sent to a 16 bit Linear Feedback Shift Register LFSR which can generate pseudo random noise with a periodicity up to 65535 2 16 1 excluding all 0 state or act as a divider In the case of the Sega Master System PSG the periodicity for the white noise is 57337 and 16 for the periodic noise The frequency of the noise is either fixed at CLOCK divided by 512 1024 or 2048 or controlled by the frequency of the third tone channel Doing this will also disable the third tone channel The so called periodic noise
19. e main settings MIDI configuration and circuit bending menu see SETTINGS Each main channel types TONE NOISE or PCM can be selected at the bottom Once in they contain different features panels that can be selected at the top and activated deactivated on the bottom right of the GUI Access to the TABLE feature see TABLES if available is done by clicking on the SEQ TABLE button These are sections are for TONE CHANNEL AMP Volume envelope PITCH Frequency Pitch envelope ARP Arpeggiator SPECIAL Advanced controls Transpose Fine tune Z80 Timer AY3 8910 Hardware envelope generator SEQ TABLE Enter in TABLE mode for the selected section where memory slots can be sequenced see TABLES NOISE CHANNEL AMP Volume envelope PITCH Frequency Pitch envelope LFSR Set the LFSR configuration White Noise Periodic or customs ones Frequency control mode from FIXED or KEY uses MIDI NOTE frequency SEQ TABLE Enter in TABLE mode for the selected section where memory slots can be sequenced see TABLES PCM CHANNEL PCM Channel as only one main panel that let you import WAV samples and control play modes See PCM Right click on a knob button or slider will open a midi learn assign menu Ctrl click move allow fine tuning THE SN76489 PSG CHIP The SN76489 N or AN Digital Complex Sound Generator DCSG is a TTL compatible Programmable Sound Generator chip from Texas Instruments a custom version was incl
20. e resolution increases for low notes and decrease for high pitched ones However you can enter non integer values in the SELECTED STEP PITCH text box and when you draw the pitch envelope the remainder part is also kept This means that you cannot draw precise semitones easily in draw mode if needed and that is what the SCALE function is used for It will scale the envelope to the nearest integer semitone value This is useful the make more complex arpeggios glissandos and runs pretty quickly Single mode is more precise This not particularly needed for non musical pitch effects SELECTED STEP PITCH It is a text box where you can type the desired semitone value for the selected step First select the desired step by moving or clicking it then enter the value in the text box click anywhere to leave You can also enter non integer values in the limit of 48 to 48 DRAW amp SINGLE Edit Mode The TONE PITCH envelope features a special edit function Draw or Single DRAW will let you draw a full shape in one quick movement SINGLE will let you move only the selected step then allows precise editing with click MAJ and for ultra precise editing click CTRL Also the step will not be changed when you click on it as in draw mode this is useful to check what value a particular step is ARPEGGIATOR This can be a quick programmable 3 notes arpeggiator or a complex MIDI driven one These 2 behavior modes PROGRAM or MI
21. e the Sega Master System Genesis bit MASK but you can also choose some WHITE ALT bit MASKS in real time that will mess with the LFSR and change the periodicity and type of noise Even the feedback bit can be changed PCM SAMPLES LOADING SAMPLES The SN76489 has not built in ability to play samples but a common trick was to output PCM sound data on the volume registers see SN76489 chip It is useful to play complex sounds effects vocals and percussions that the chip alone could not reproduce SPSG has 3 SLOTS to load sample data from wave files WAV and will play them like on the Master System with a crunchy sound Click on the LOAD folder to browse your hard drives and load WAV files There is a volume slider for each of the 3 PCM slot The pitch sliders control the playback rate SLOTS are MAPPED to standard midi GM drums MIDI CH Notes like so MIDI MAPPING for DAC SAMPLE SLOTS Slot 1 MIDI notes 35 36 KICK Slot 2 MIDI notes 38 40 SNARE Slot 3MIDI notes 42 44 46 HIHAT PCM amp PWM The logarithmic nature of the PSG volume versus linear PCM data will also give the samples a characteristic sound if you use Pulse Code Modulation method PCM Fig1 PSG volume If the sample data is to quiet you may have bad results so be sure to have volume optimized sampled source Data sample can be rescaled before being outputted to the PSG to maintain the natural linearity of the original data
22. eginning and change it to noise a moment later As you can see the waveform now looks a bit more like the original and has a beefy attack Another method to make an interesting snare often used by e g Rob Hubbard I think is to vary the noise frequency with a multi octave arpeggio If you need a real world analogue you could think the cycling noise frequency low hi low hi etc as reverberation Fast Arpeggios One common technique to override the limitation of mono only channels and the inability to play chords without using all available channels was to play fast arpeggios The result will sound as a chord to the human ear and can produce an awesome harmony with many channels Arpeggios do not necessarily need to be looping forever they can also enhance the attack of a sound In addition to this bending from one arpeggio to another will result in a more natural feel The MIDI mode of SPSG arpeggiator lets you create very complex nonlinear arpeggios in real time as you play the melody This was at the time pretty time consuming to program and thanks to composers like Tim Follin we have had some great use of this effect Echoes amp Reverbs These primitive sound chips rarely comes embedded with a DSP effect processor so again composers had to imagine some tricks to overcome the limitation and add more depth to the music You can see an echo effect in to ways a mono echo which will be made only by repetition of the previous vo
23. en assembled through the SYNTHEDIT engine using the very last version custom C coding and some third party licensed code It may be ported to OSX at some point in the future ________________________________________________________________________________ Thanks to all the nice people that started to use SPSG and support my projects A special thanks to SMS org Maxim and TmEE also Sebastian Tomczak who designed the SMSN GENMDM midi hardware interface and provide great sources of inspiration and to Yuzo Koshiro and Alberto Gonzales Mc Alby for their music and support on SPSG Full Credits amp Thanks can be accessed on the SPSG GUI panel Mainly SPSG can act either as the SN76489AN CH1 2 3 or CH4 Noise channel It can be either polyphonic copy the settings to 3 voices or mono like the real chip and can act as 3 SN76489 Tone channels at once with the same patch when in poly mode The Noise channel is always mono and can be controlled separately PCM samples can also be played and controlled separately through the Tone volume register In addition to the above software Timers are provided to produce some unusual Tone modulation by writing to the volume register and an emulated AY3 8910 Sound Chip Envelope generator part is available to produce some classic and not so classic Buzzers type of sound However you have to load 3 instances of the VST to have 3 really independent Tone channels This particular implementation allo
24. er 3 Load it in your DAW INSTALL STANDALONE 1 Decompress the downloaded archive file 2 Copy the entire Folder SPSG_STANDALONE where you want 3 Simply RUN SPSG exe State of SPSG current features WIN 32 VST runs on 32 64Bit Systems and it is multicore compatible HIGH QUALITY GUI Different panels for controls etc INSTANT UPDATE FOR ALL CONTROLS FULL MIDI AUTOMATION With midi learn right click to assign MIDI 3 CHANNELS POLY amp MONO MODE With Portamento Control DIRECT CHIP OUTPUT OR CONSOLE FILTERING Sega Master System or Sega Megadrive Genesis SN76489AN classic features SUPPORT ANY CLOCK RATE From 1 MHz to 4 MHz like the real chip 1 64 STEPS Amplitude Envelope Generator 64 steps persistent memory up to 300 Hz synced or independent speed rate loop ping pong and release step 1 64 STEPS Pitch Envelope Generator 64 steps persistent memory up to 300 Hz synced or independent speed rate loop ping pong and delay LFO VIBRATO For quick expression INTERNAL ARPEGGIATOR Programmable or live controlled via MIDI Input MEMORY SLOTS amp TABLES 8 memory slots per envelope arpeggiator and advanced waveforms than can be internally sequenced at any available clock speed can be used as a wave table for software waveforms PCM amp PWM 4 slots to load any PCM WAV files auto converted to mono that will be played to the SN76489 volume register on one or three channels at the time SN76489AN extended features AY3 8910
25. i parameters via the SETTING panel will also send MIDI OUT message The MIDI OUT Channel is also chosen via the panel All assigned MIDI parameters will send MIDI OUT data on global patch change SPSG can send MIDI CC amp PITCHBEND data over any MIDI channels For example if you assign MIDI CC 11 to the volume amplitude register of the Tone channel when it is changed SPSG will also send the volume envelope CC 11 DATA over the chosen MIDI channel and also PITCHBEND DATA for ARP or PITCH ENVELOPE Pitch Bend output resolution is 48 semitones that means that the receiver must also be in that resolution to receive correct pitches You can send these MIDI commands first to make sure it will gt gt CC 101 Value 00 gt gt CC 100 Value 00 gt gt CC 6 Value 48 which is the number of PB semitones This MIDI OUT feature for AMPLITUDE and FREQUENCY is useful if you want to convert SPSG commands to a VGM file that can be embedded into some machine code or played on the console itself A free tool called M2v_PSG Midi gt VGM Converter SN76489 by Valley Bell can be used to convert MIDI data to VGM it will recognize MIDI CC 11 as volume envelope and can handle SPSG pitch bend message well if you embed the previous MIDI command at the beginning of you MIDI track However my tests with high speed envelope rates above 40 or 50 ticks per seconds might result in errors in this program so keep in mind to stay under 40 ticks or experiment Time
26. ilable will provide a programmable sequence of memory slots up to 50 steps with 1 to 16 repetition of each slot Independent sequenced tables are available for AMP PITCH ARP SPECIAL amp LFSR section of SPSG The speed of the TABLE can be as fast as 300Hz These tables allow for complex volume pattern to be made exceeding the 64 steps limit of envelopes like custom mono delay rhythmic patterns complex runs amp arpeggios many pitch effects and completely original LFSR modulations see NOISE A special mark as to be made for the SPECIAL amp LFSR panel controls possibilities with tables The SPECIAL memory slots store much more parameters than any other one and can then provide very complex sequences of effects wavetables evolving sounds etc This is the same for the Noise LFSR IMPORTANT DO NEVER RECORD AUTOMATION WHEN A TABLE IS RUNNING IN THE SPECIAL OR LFSR PANEL THIS CAN LEAD TO UNPREDICTED RESULTS AS THE RECORDED AUTOMATION IS ALWAYS SMOOTHED OUT IN MANY DAWS THE INTERNAL STATE OF THE TABLE WILL FIGHT WITH THE RECORDED AUTOMATION DATA Unless if you want to mess it up in a creative way HINT You can still use separate instances of SPSG VSTi to combine TABLE featured tracks and non TABLE featured automated ones or you can also record your own automation in a DAW that can act as tables Usage of Tables As soon as you push the SEQ TABLE button you will enter in TABLE MODE for this particular section
27. logspot com Facebook News www facebook com alyjamesound Youtube Channel www youtube com alijamesproduction Soundcloud demos http www soundcloud alyjameslab Twitter alyjamestwitt CONTACT alyjames info gmail com External links SN76489 reference by SMS org http www smspower org Development SN76489 GENMDM http little scale com HOPE YOU HAVE FUN WITH SPSG DISCLAIMER amp LICENCE AGREEMENT DISCLAIMER SPSG the software is provided as is without warranty of any kind Aly James Lab alyjames info gmail com the Author disclaim all warranties relating to the Software whether express or implied including but not limited to any implied warranties of merchantability and fitness for a particular purpose and all such warranties are expressly and specifically disclaimed The Author shall not be liable for any indirect consequential or incidental damages arising out of the use or inability to use the Software even if the Author has been advised of the possibility of such damages or claims The user of the Software bears all risk as to the quality and performance of the Software If your computer blows up I say I wasn t there of course that should not happen LICENCE AGREEMENT SPSG is copyright 2013 2014 Aly James SPSG the software is not public domain and is protected by the copyright laws of the international community In using SPSG you are not obtaining title to SPSG or any copyrights
28. lume at a later time with a quieter value or a polyphonic echo which will use quickly other channels to reproduce the envelope with a delay The later gives better results at the cost of 1 or 2 channels during the effect This is easily made with a DAW and SPSG first be sure to be in MONO mode then open any built in Stereo Delay plugin and be sure to have no feedback or damping effect Just set one repetition on LEFT side and one later on RIGHT side This will shine any SID type of Lead sound really well Reverb can be simulated well with 3 channels by simply letting the sound decay while another note is played AY3 8910 Buzzers The use of the built in envelope generator to produce some nasty sounds has been a huge part of the hype later my implementation of the SID technique with TIMER on a real Master System also offers to possibility to have a more nasty sound particularly good for leads Sequence different shapes and you will get a retrigger on each changes this will produce a nice rhythmic effect Now combine this with the Tone channel and optionally sync the envelope with a TIMER and you will be able to reach some really interesting sounds You will need to experiment with different tuning between these 3 sources to obtain some awesome effects or harmonic tones I will add more information in future revision of this manual LINKS Aly James centric links Official Website www alyjameslab com Dev Blog www alyjameslab b
29. more or less out of tune results that can be used creatively TONE RETRIG When set to FORCE it will try to reset the phase of the TONE by very quickly writing 0x000 to the TONE frequency register before writing the actual frequency This is very useful to synchronize the phase with the TIMER or HARDWARE in order to produce a more predictable modulation each time you press a key HARD SHAPE SELECT Clicking on the waveform shape will switch between the 4 possible looping HARDWARE envelopes each change will retrigger the envelope TIMER SQUARE Clicking on the TIMER type will switch between the normal SQUARE interrupt routine and the CUSTOM 4 bit waveform one When you activate the TIMER CUSTOM you will be able to select from 8 MEMORY SLOTS to store a 4 bit waveform shape by clicking on the small memory shape number EDIT SHAPE will open the edition panel display where you can draw each of the 16 bytes Note that the EDIT SHAPE panel will update immediately when you change memory shape slots but the central display will only update if a key is pressed an a note is played Additional Controls The clever use of different frequencies between TONE TIMER amp HARWARE can produce a lots of interesting effects some harsh and some more mellow this is a great way to experiment and this is why you have a transposition and fine tune control available in the SPECIAL panel An OCT switch is provided to limit the transposi
30. n be clocked to this SYNC BPM or can have an independent clock source LFO the frequency of the LFO Vibrato ranges from 3 98Hz to 72 2Hz like on the YM2612 Vibrato applies only on TONE channels Set in to minimum to disable when not in use this will also saves CPU PMS Pitch Modulation Sensitivity vibrato applies only on TONE channels Note that as the pitch resolution of the SN76489 sound chip will decrease the higher the notes so will be the resolution of the vibrato This means that a small modulation setting cannot be heard any more on high octave PMS EFFECT ON PITCH 0 1 2 3 4 5 6 7 No effect Displacement of 3 4 Displacement of 6 7 Displacement of 10 Displacement of 14 Displacement of 20 Displacement of 40 Displacement of 80 Percent of a halftone SETTINGS Access the main settings of the VST like MIDI IN OUT channels configuration Sound chip output filtering Pitch Bend Range Mono Poly and Portamento See SETTINGS CH TONE Enters the TONE channel panel CH NOISE Enters the NOISE channel panel CH PCM Enters the PCM channel panel Last but not least an oscilloscope display lets you see the changes in the waveform SETTINGS The Global settings panel lets you assign the MIDI IN channels that will control each sound source TONE NOISE amp PCM This is where you can set the MASTER CLOCK rate of the SN76489 chip You
31. of steps played can be automated in real time and will not discard the steps previously set if you reduce the number dynamically SPEED Is a clock speed multiplier it will multiply the AMP CLOCK by the amount ex CLOCK 120 SPEED 2 will play each step at 120 2 240 BPM SLOTS There are 8 MEMORY SLOTS available these are memory storage for the 64 envelope steps levels you can switch between them via automation at any time for complex envelopes and even sequence them with TABLES see TABLES You can also COPY a MEMORY SLOT to another via the COPY FROM button CLOCK This is the main CLOCK of the envelope in BPM it is the principal parameter to calculate the envelope step final speed If you click on the SYNC button the CLOCK value will turn green and will be controlled by the main SYNC value SYNC slider on the main panel LOOP Is the number of steps that has to be played before activating the LOOP mode For example let s say we have set a 16 steps envelope then if you set the LOOP parameter to 32 the result will be gt gt PLAY the 16 STEPS gt gt WAIT for 16 STEPS gt gt PLAY AGAIN from STEP 1 and so on Basically set it to 2 to LOOP endlessly RSTEP Is a special feature that when set above 0 will apply an automated high resolution release curve to the final step The higher the setting the longer the release tail will be This is also useful for quick simple decaying envelope just set th
32. oland 909 bass drum However if we look at a more interesting and louder kick sound we will notice it s not just a sine wave There are higher frequencies there even though they are not that pronounced A good thing to do is to combine the soft sine wave triangle wave is a nice approximation with something sharper and louder in the first moments of the kick Try having a few milliseconds worth of square wave and or noise in the beginning of the drum Then continue as usual with a low frequency tail To simulate a distorted drum use the square waveform As in the example below you can see a hard limited sine wave looks like square wave An analysis of the kick drum sound used in Auf Wiedersehen Monty confirms the ideas discussed above It begins with a triangle wave which is active for 20 Ms one program tick There after there is a short noise part for 20 Ms It ends with a pulse wave the frequency and amplitude gets lower Snare drum Creating a convincing snare drum starts to get a bit complicated It helps if we once again look at what is actually happening in a good snare sound As you can see the snare sound consists of noise and a lower sine wave sound the low frequency hum is the drum membrane vibrating Also the beginning of the hit the low sine wave is louder than the noisy rattle which adds a nice punch We can emulate this by having a short pure triangle wave tone use square wave to make it louder in the b
33. ple who documented the SN76489 on the web You know who you are It started out as a simple but accurate SN76489 emulator then slowly turned into a complex featured synth I wanted to make any sound possible with the chip included some of the features the AY3 8910 had and also circuit bent the technology used to produce the noise channel It turns out to be quite nice so I decided to make it public in exchange for a small donation for the large amount of work I put into this The goal was on one hand to make a bit perfect SN76489 emulation with control over the master clock frequency because as you will learn latter in this manual the frequency range that can be played by the chip highly depends on the master clock On the other hand 3 square wave generators and 1 noise periodic generator can be pretty limited if used in a basic way which is why I have experimented what could be done on the real chip to produce extended modulation options In the end I have implemented those experiments results into the VST an also added the AY3 8910 hardware envelope part and a nice circuit bending option for the noise generator All and all the SUPER PSG EXTENDED emulation turns out to be a fantastic 8bit synth suitable for chip music and Sega nostalgic pleasure and also a powerful tool for modern music production This emulation uses a totally new core with band limited waveforms excepted for the Timer waveforms which are raw The product has be
34. r amp Buzzers are not supported as they modulate at audio rate The MIDI OUT will also be able to control any microcontroller capable of handling MIDI data and transferring them to a real SN76489 chip CC 101 Value 00 gt gt CC 100 Value 00 gt gt CC 6 Value 48 HARDWARE OPEN SOURCE HARDWARE An open source code solution for microcontroller is available on request based on my modified version of Sebastian Tomczak Sn76489 code You can build your own SN76489 MIDI interface and used my modified code to use it with SPSG as a controller Fig1 DIY SN76489 MIDI INTERFACE amp GENMDM GENMDM The GENMDM is a midi hardware interface created and designed by Sebastian Tomczak that allows the real SEGA MEGADRIVE GENESIS to understand MIDI data It means you can control the YM2612 FM chip amp the PSG sound chip built in in real time via MIDI My FMDrive VST takes care of the FM part See FMDrive VST at alyjameslab com SPSG can act as a visual controller for the PSG providing complex envelopes and allowing more user friendly control the parameters and visual feedback See the GENMDM Control MANUAL The VST plugin can control the GENMDM by setting the appropriate MIDI CC on each parameter Some of the extended features are not available yet on GENMDM such as TIMERS AY3 8910 emulation and custom parameters Some are still in development and could be implemented in future SPSG and GENMDM updates GENMDM is no longer available a
35. s calculated by dividing the MASTER CLOCK by 256 EP 16 bit Envelope period The AY was usually clocked at 2 MHz this calculation allows a relatively good resolution for slow period as low as 0 1 Hz but will greatly reduce fast period resolution and will top at 7812 5 Hz This is why it was only mainly used for bass lines has it will be out of tune pretty quickly on higher octaves Fig 1 shows the looping shapes in red are the looping ones and the ones that you can set in SPSG Fig 3 shows the envelope possible levels Emulating the envelope generator as to take in account that the Hardware envelope counter is 16 bit versus the SN76489 frequency is 10 bit So you have to binary left shift by 3 8 the envelope period to obtain the desired frequency on the PSG Doing the opposite will result in precision loss and will not produce perfect pitch synchronization This technique as its counterpart because it will reduce the high notes resolution of the PSG this will also apply the same precision loss on high pitched notes the hardware envelope has SPSG internally uses a FREQUENCY RATIO from 1 1 that tries to apply the PSG frequency to the hardware frequency with precision loss to 8 1 that will produce a more similar pitch A liberty has also been taken on the original design to allow the hardware frequency to cover the DCSG range This graphic shows the differences between Tone and resolution at 1 1 ratio Hardware frequency and also demon
36. strate that the hardware can produce very low frequencies that the SN76489 alone cannot LIMIT OF SN76489 LOWEST FREQUENCY LOSS OF PITCH DEFINITION The frequency of the tone being 10 bit versus 12 bit for the AY tone you will need to lower the Master CLOCK frequency of the SN76489 chip to obtain possible modulation on lower octaves You can also disable the tone and only use the HARDWARE generated waveform by forcing the tone period to ZERO You can then use the hardware waveform alone as a saw or triangle bass tone and as you will see in the features details also use the TIMER to synchronize the hardware envelope Because each time the internal Hardware register is rewritten by the TIMER it will restart the envelope it allows sync type effects also known as SYNC BUZZERS The use of different frequencies between TONE TIMER amp HARWARE can produce a lots of effects some harsh and some more mellow this is a great way to experiment and this is why you have a Transposition and fine tune panel available Main Special Controls 3 WAY BUTTONS SELECTOR These buttons let you switch between normal TONE output with no modulation TIMER or HARDWARE modulation IMPORTANT when HARD is selected it will completely disables the AMP envelope any setting will have no more effect on the volume PM When ON this button will send the ARP amp PITCH ENVELOPE modulation to the TIMER amp HARDWARE TONE PERIOD
37. t the moment HIDDEN SECRETS Video Game Composers techniques A huge part of the feel from video game music sound of the past is that composers had to use lots of trick to make the most out of these simple sound generators the following information s might help you when you are trying to design new sounds with a particular purpose Drums amp Percussions As you will see analyzing a real word drum sound sample visually will help you a lot to understand the nature of the changes in the sound The TABLE features my help a lot to create a wavetable First let me share with you this article on chip drums found at http kometbomb net 2011 10 11 chiptune drums Hi hat We ll start with the easiest drum Generally just a stable noise waveform with a sharpish attack and a longer decay is enough If a filter is available filtering out the low frequencies with a high or band pass filter helps to make the other rhythm sounds stand out you don t want the hi hat to drown out the snare For a shaker type sound make the attack phase longer Kick drum Kick drum is a quite simple drum as well if you need a basic techno kick or longer 808 style sine wave oomph The theory behind a basic kick goes like this start high finish low Make the amplitude and the frequency drop sharply If you hear a sharp decay in the frequency you will perceive it like something punching through the other sounds This example below is a generic R
38. tion to octave only for great musical effects TRANS amp FINE Provide a separate 48 semitones 4 Octave UP amp DOWN control over the TONE TIMER amp HARDWARE frequencies And additional FINE slider will be often used to detune one voice from another and to control the beating effect and modulation between them Each parameter can be incremented and decremented by 1 via the arrows at the top SLOTS There are 8 MEMORY SLOTS available these are memory storage for most of the SPECIAL panel settings you can switch between them via automation at any time for complex evolving sequence and even control them with TABLES see TABLES You can also COPY a MEMORY SLOT to another via the COPY FROM button Here is a table that shows which parameters are saved within these SLOTS and which don t SAVED PARAMETERS FIXED NON SAVED PARAMETERS TONE TIMER HARD SELECTOR PM HARD SHAPE SELECT TIMER SQUARE CUSTOM TIMER CUSTOM MEMORY SHAPE TRANSPOSE SETTINGS FINE SETTINGS TONE PERIOD HARD SYNC HARD RETRIG FREQ RATIO TONE RETRIG These complex modulation under the SPECIAL panel where usually hard to program on these sound chips without going low level with assembly programming language and this is when TABLES will be useful which is fine because it is our next section TABLES The sequenced table when ava
39. tive results The volume setting is then used as a 4 bit DAC All three tone channels can be used together to get maximum volume if needed The logarithmic nature of the PSG volume versus linear PCM data will also give the samples a characteristic sound if you use Pulse Code Modulation method PCM Data sample can be rescaled before being outputted to the PSG to maintain the natural linearity of the original data however with particular settings the output of not rescaled data sample can act as a transient enhancer of some sort PWM method is basically a raw 1 bit MAX volume or MIN volume conversion of the sample data and will therefore be louder than PCM method MAIN CONTROLS Each channel is selectable to control or edit via the 3 select buttons CH TONE CH NOISE and CH PCM Setting LFO to minimum also disable vibrato generator saving system memory resources when not in use Common Parameters TONE Tone channel general volume multiplier can also be MIDI assigned to an external CC with AMP envelope deactivated to play data from a VGM MIDI transcoded track NOISE Noise channel general volume multiplier can also be MIDI assigned to an external CC with AMP envelope deactivated to play data from a VGM MIDI transcoded track PCM PCM data general volume multiplier SYNC Is a value in BMP that serves as a master clock for any SYNCED AMP PITCH and ARP envelopes As you will see later each envelope ca
40. tton CLOCK This is the main CLOCK of the envelope in BPM it is the principal parameter to calculate the envelope step final speed If you click on the SYNC button the CLOCK value will turn green and will be controlled by the main SYNC value SYNC slider on the main panel LOOP Is the number of steps that has to be played before activating the LOOP mode For example let s say we have set a 16 steps envelope then if you set the LOOP parameter to 32 the result will be gt gt PLAY the 16 STEPS gt gt WAIT for 16 STEPS gt gt PLAY AGAIN from STEP 1 and so on Basically set it to 2 to LOOP endlessly DELAY Will wait x DELAY amount of steps before triggering the pitch envelope this is very useful when you don t want to apply a pitch modulation immediately after a key on DISPLAY MAX amp MIN The pitch envelope ranges from 4 Octaves down to 4 Octaves up It is a value in semitones where 12 1 Octave you can set the MAX and MIN value of the envelope and the display will scale accordingly Note that if a previous step was out of the new range it will not be rescaled only new entered step value will SCALE Will scale the envelope to the nearest integer semitone value As The SN76489 got 1024 possible frequency values we can simplify this linearly and say that we can adjust the pitch to 1 8 of a semitone so the chip can recognize 0 25 1 8 of a semitone This is actually not totally true because th
41. uded into the Sega VDP chip It contains three square wave tone generators and one white noise generator each of which can produce sounds at various frequencies and sixteen different volume levels It has been used in lots of arcade systems and consoles and was generally clocked at 3 5 MHz NTSC PAL witch limited the bass response available the chip can be clocked between 1 to 4 MHz The lower the clock the lower the frequencies available but also there will be high frequencies precision lost The way these sound chips calculated the frequency was usually by dividing the master clock which results in a lack of precision on higher frequencies These limitations are a noticeable part of the characteristic sound of the PSG when you use it in conjunction with other sound source such as FM Because the chip will never be perfectly in tune this gives movement in sound This graphic shows the SN76489 frequencies available in regard to a linear frequency sweep Frequencies are set via a 10 bit register 1024 values and counted down until they reach 0 at which point the output waveform for that channel will toggle 0 or 1 and the counter will be reloaded This counter usually runs at 3 5MHz Master System Genesis the same clock as the Z80 processor For reference the 10 bit FNUMBER can be calculated this way Th
42. ws getting over the original channels limit if ones need it It also simplifies automation control as there are a lot of parameters for a single channel It was unnecessary to implement an internal echo feature as every single DAW features a Stereo delay that can be set to produce a classic 2 or 3 PSG channel delay easily A delay greatly enhances some PSG sounds particularly if you use the chip as a single instrument among a complex composition just remember to limit the polyphony to 3 for accuracy Basic MIDI implementation MIDI IN SPSG can receive any MIDI CH as main source for notes and key on off Independent MIDI IN can be set for TONE NOISE and PCM source control MIDI OUT SPSG can send MIDI CC amp PITCHBEND data over any MIDI channels For example if you assign MIDI CC 11 to the volume amplitude register of the Tone channel when it is changed SPSG will also send CC 11 DATA over the chosen MIDI channel and also PITCHBEND DATA for ARP or PITCH ENVELOPE Pitch bend output resolution is 48 semitones allowing to send the amplitude envelope to the hardware or for example to make a MIDI track suitable for VGM conversion INSTALLATION COMPATIBILITY SPSG is a Windows 32Bit VST Instrument for use with MIDI capable DAWs RUN on 32 64 Bit Systems If you want to use it with a 64bit DAW you can use JBridge or internal DAW Bridge INSTALL VST 1 Decompress the downloaded archive file 2 Copy the entire Folder SPSG to your VST PLUGINS fold
43. y modes FIXED will use any of the 3 FIXED FRQ available the MASTER CLOCK divided by 512 1024 or 2048 and will not receive any pitch modulation The other mode will use the frequency of the third channel and will received pitch modulation SPSG internally route for convenience the frequency signal independently so the frequency that will be used in KEY mode will be the actual key played frequency KEY FOLLOW When FRQ CONTROL is in KEY mode you can specify if the NOISE frequency will follow the keys the pitch envelope or ONLY the pitch envelope precisely the played frequency divided by 16 see SN76489 CHIP Linear Feedback Shift Register LFSR An LFSR is a common technique in electronics derived from the shift register in order to produce complex patterns with the longest period possible The relative randomness of the process is highly based on the number of bits in use and the clever usage of XOR bits XOR is a logic operator The SN76489 features a 15 bit LFSR but the SEGA custom one that is modeled here was 16 bit The XOR bits or Tapped bits are B0 and B3 MASK 0x9 fed back into B15 This particular configuration results in a relatively good periodicity of 57337 for the WHITE NOISE However a choice of a different bit mask such as MASK 0x81 would have result in a better periodicity of 63457 Notice that even the so called white noise is in fact periodic You can easily hear a change in frequency an even recognize a note
44. you will obtain another raw waveform this can be used to play another software voice or to modulate the actual TONE A common technique on these basic sound chips is to create a pulse width modulation on the TONE channel even if the chip can only generate a fixed 50 50 duty cycle square wave This technique commonly used on the ATARI ST scene was named the SID sound or SID voice as it mimics the type of moving lead sound the C64 sound chip SID 6581 was able to produce Another possibility is to use a Timer Interrupt to trigger a little 4 bit sample of a 1 cycle waveform this will produce a completely new waveform to use alone or as a SID modulator The way the frequency for the Timer Interrupt is calculated allows for an acceptable precision A possible use with Z80 is the Horizontal Blank Interrupt As you will see for the emulated AY3 8910 HARD envelope generator a frequency ratio conversion is available to adjust the pitch AY3 8910 Hardware Envelope The AY3 8910 PSG has a built in basic envelope generator that can replace any written amplitude data by the output of the envelope The start en end value is always MAX or MIN 4 Particulars envelope types are interesting because they will automatically loop this is how when the envelope period reaches the audio range it can output a SAW RAMP or TRIANGLE type of waveform also known as BUZZERS The AY Envelope had 16 steps versus 32 for the YM2149 The envelope period i
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