ECE352: Signals and Systems II - Spring 2007
Contents
1. Plug some headphones into the headphone jack on the front of the PC Click the triangular PLAY button in the Sound Recorder window to playback the recorded stereo sound to validate the quality of the recording Finally save your recording by selecting File gt Export As WAV Select a filename and location and click Save To import the saved recording in wave format into the Matlab environment use the on line Matlab HELP resource to investigate the use of the built in Matlab function wavread Use script line x fs nbits wavread filename to import your recording into a Matlab array x of dimension samples x 2 The first column contains channel 1 audio samples and the second column has the samples from channel 2 audio If you get only one column then the recording was incorrectly recorded in Mono rather than Stereo Look at the values of fs and nbits to verify that they correspond to the attributes that you selected when creating the file with Sound Recorder To have Matlab reproduce the recorded two channel sound so that you can listen with either headphones or powered speakers use the script sound x fs to hear the stereo recording If you want to listen only to channel 1 then use sound x 1 fs or change to 2 to listen only to channel 2 5 3 Camera Image Acquisition Obtain a usb camera with attached USB cable from your lab TA Plug the camera into a USB port on the front of your lab PC Windows drivers have2. 2 3 Acquire USB camera imagery and display as color image and as separated red green blue RGB image planes 3 References Course text Section 4 5 sampling and page 429 quantization Following reference documents may be found on the ECE352 web site 1 Tektronix CFG250 function generator user manual TekFunctionGen_User_Manual pdf 2 Tektronix TDS210 digital oscilloscope user manual TekDigScope_User_Manual pdf 3 Dell PC user guide Dell_user_guide pdf 4 Pre Lab Tasks 0 pts Read and familiarize yourself with this entire assignment prior to start of lab Bring scope probe from your prior labs Bring some headphones to listen to recorded audio lab PCs may not have built in speakers 5 Lab Tasks Experiments Future laboratory assignments will involve acquiring data performing operations on the acquired data related to concepts covered in the course textbook and lectures and making comparisons between measured and theoretical signal responses This laboratory assignment will acquaint you with data acquisition processes for three signal sources and will make you aware of some acquisition issues related to data fidelity 5 1 Oscilloscope Displayed Waveform Acquisition Connect two probes to channels 1 and 2 of the oscilloscope Select probe attenuation settings to either 1X no attenuation or 10X attenuation by a factor of 10 Make sure your interpretation of the voltage levels seen on the scope screen refle
3. already been installed on the lab PC so that it should automatically recognize the camera In MATLAB enter the following two commands to set up a video object with which to capture individual frames in RGB color vid videoinput winvideo 1 YUY2_ 160x120 vid ReturnedColorspace rgb Once the object is ready you can preview the output of the camera using preview vid To acquire an image from the Matlab command window type in the command pic getsnapshot vid This will automatically capture and load a 160 x 120 x 3 array of uint8 pic you may select another variable name of your choice with the captured image The image consists of 120 rows x 160 columns of pixels each pixel of which is expressed in the three RGB red blue green colors of 8 bit un signed integers uint8 per color 0 is dark and 255 is brightest intensity for a color total of 24 color bits per pixel To see the image within Matlab use on line Matlab HELP for utilization of function image and simply type in the command image pic An image comparable to the image of a Rubick s cube below will then be generated within a Matlab figure window 10 You will need to save the images in your working directory You can use the MATLAB command imwrite to save images in bitmap format imwrite pic filename bmp BMP You can also load previously saved bitmaps using imread pic imread filename bmp BMP After experimenting wit
4. amplitude direction is typically specified in number of bits used to quantify the amplitude levels Frequently encountered bit lengths are N 8 10 16 32 bits The total number of levels quantized is 2N indexed from 0 to 2 1 for uni polar waveforms or 2 2 to 2 2 1 for bipolar waveforms Thus an 8 bit quantization produces 256 quantized levels and a 16 bit quantization produces 65536 quantized levels In order to capture the digitized waveforms observed on the scope for insertion as a plotted figure in your lab report a 3 step import export procedure involving Excel Matlab and Word is required The data will be saved as an Excel formatted file xls you will provide the file name when saving Your lab TA will provide instruction on how the dual channel acquisition is done A scope acquisition always captures a fixed horizontal time axis sampling of 10 000 samples to cover the 10 graticule divisions observed along the time axis The vertical amplitude of each scope waveform is quantized to 8 bits 2 256 levels such that each vertical graticule division seen on the scope display is represented by 25 levels of quantization it would require a displayed waveform therefore to extend over 10 24 divisions to see all 256 possible levels After invoking an acquisition the Excel spreadsheet will have three columns filled each with 10 000 values Column 1 contains the 10 000 time axis sample times in seconds column 2 has the 10 000 scope cha
5. color planes and also combined to create a gray scale image Use the Matlab HELP facilities to examine the use of the command rgb2gray located in the Matlab Image Processing Toolbox for converting an RGB based image to a gray scale based image Your task is to create a new Matlab function name it color_separation m that takes your original saved image and 1 creates individual gray scale and single color images of each of the separated red green and blue image planes and 2 constructs a large image array combined_pic color_separation your_pic 12 composed of these four sub images This can then can be displayed image combined_pic as illustrated below for the cube image 20 40 60 60 100 20 40 60 80 100 120 140 160 7 Lab Report Use the lab report format to be provided by the TAs 13
6. to WAV Microsoft 8 bit PCM For 16 bit set it to WAV Microsoft 16 bit PCM Before starting the recording process make sure the microphone volume is set to maximum in the Windows volume control Right click on the volume in the taskbar and select Recording Device which will bring up a window like the one shown below on the left Right click on the High Definition Audio Device microphone and select properties Go to levels and slide the volume all the way up fi lt it Sound 4 8 ej 7 Miche Popes Playback Recording Sounds Communications General Listen Levels Advanced Select a recording device below to modify its settings Microphone Microphone High Definition Audio Device a Line In Microphone Boost B Set Default M Properties Configure You are now ready to create and save an audio recording While talking in the direction of the microphone click the record button to start recording Record a few seconds of your voice using a common phrase for example This is a test of audio recording at the same level and distance from the microphone for each set of selections then click the STOP button to end recording Make sure you are recording in stereo as evidenced by two audio tracks being shown x Audio Track Y 1 0 eee cl a Pn Rn
7. ECE352 Signals and Systems II Winter 2014 Laboratory 1 Assignment DATA ACQUISITION IMPORT AND EXPORT Lab Dates two weeks 1 and 2 Lab Report Due Date At the beginning of the lab on Jan 21st for Tuesday session Jan 22nd for Wednesday session Jan 23rd for Thursday session Jan 24 for Friday session 1 Introduction This laboratory will familiarize you with the processes for a acquiring digitized data from three sources b importing the acquired data into Matlab c generating graphics of the acquired data using Matlab and d exporting the Matlab graphics to a file for later importing into your lab re port The sources of acquired data include 1 digitized voltage waveforms observed on the lab oscilloscope 2 digitized acoustic waveforms from a microphone and 3 imagery from a digital video camera All acquired data and processed byproducts graphics in this assignment will be stored as files in an ECE352 specific lab folder created within your per sonal engineering server directory This will permit access outside the lab to prepare your lab report Note The video functions will require the R2010b64 version MATLAB When started you must log on to the ENGINEERING domain using a username of ENGINEERING accountname and your engineering password 2 Objectives 2 1 Acquire oscilloscope waveforms and observe quantization effects 2 2 Acquire stereo audio signals from a microphone and observe quantization effects
8. ct your choice of either the 1X or 10X setting Perform probe compensation as needed using the procedure discussed on page 6 of the oscilloscope manual Attach a cable with clips to the function generator and attach the probes to these clips Set the function generator frequency amplitude and DC offset controls to create a 10 KHz symmetric triangle wave of 1V to 1V peak to peak amplitude range Select a SEC DIV setting that will display approximately 5 periods of the symmetric triangle wave Adjust channel 1 POSITION and VOLTS DIV controls such that the peak to peak waveform display covers 10 graticule vertical divisions which should cover from the bottom to the top of the visible graticule markings Adjust channel 2 POSITION and VOLTS DIV controls such the peak to peak waveform display of the same waveform covers a smaller extent of only 1 vertical graticule division 2960 2970 2980 2990 3000 3010 3020 3030 3040 The waveforms that you see on the scope screen have been digitized This means that not only has the waveform been sampled in time temporal quantization along the horizontal axis as Shown in the figure above but also quantized in amplitude level along the vertical axis using an electronic circuit known as an analog to digital converter ADC The quantization in the temporal direction is typically specified as a sampling rate in either samples per second sps or more commonly and equivalently in Hertz Hz The quantization in the
9. h the camera and the effect of lighting conditions on the quality of the camera imagery your task here is for each lab partner to acquire and save the image of the other lab partner s face 6 Post Lab Tasks 6 1 Oscilloscope Waveforms Generate labeled and captioned Matlab created figures for each of the two waveforms saved from Task 5 1 Use the same vertical and horizontal scaling for both figures Avoid numeric labeling of the time or amplitude axes that involves exponential powers of ten by selecting sec msec or usec for the time axis and V or mV for the horizontal axis Recall from ECE351 the process of exporting Matlab figures into other applications like MS Word While in the Matlab window select File gt Export and save the Matlab figure window as a tif file recommended al ternative formats are jpg bmp and emf Question Examining the two plots of the waveform taken at different vertical scope gain set tings how does the selection of the Volts div setting affect the fidelity of the saved waveform Question What are the implications for saved scope waveform data that you may make in future labs if you want to achieve saved scope waveforms of highest fidelity 6 2 Dual Audio Signal 11 Generate labeled and captioned Matlab produced figures for a 0 1 second audio segment of the waveforms you recorded in Task 5 2 Use the Matlab subplot function to create figures in which the top half is a plot of channel 1 aud
10. io and the bottom half is a plot of channel 2 audio for the 0 1 second audio segment use a common vertical scaling and a common time axis interval The Matlab function wavread scales the signed 8 bit or 16 bit quantized integer sample values pro duced by the Sound Recorder application to floating point values in a range between 1 and 1 max by dividing the integer values by 2N To restore the original integer sample values scale the floating values by 2 1 for either N 8 or N 16 Question What percent of the maximum integer discretization range did your recorded wave forms use in each of the 5 recording conditions Question Are you able to hear and see in the plots perceptible quality differences among the 5 recordings due to the differences in the degree of quantization The sampling rate The volume control setting What are the implication for future audio acquisitions in order to maintain highest fidelity recordings Question Based on your listening tests what are the implications for obtaining the highest fidelity audio recordings in terms of the three parameters that can be selected fs nbits volume level 6 3 Camera Imagery The analysis of imagery often is simplified if each color is processed separately or if the colors are combined into a single image in which only the illumination level changes gray scale In this task you will devise Matlab operations that will separate the imagery you acquired into its individual
11. its 16 volume full 5 fs 11025 Hz nbits 8 volume full To make an audio acquisition first start Audacity from the Windows environment A window as shown below will appear File Edit View Transport Tracks Generate Effect Analyze Help l 4 Eo 24 12 a Pa ais 24 12 d cers z OF 1 0 4 Project Rate Hz Selection Start End Length eae 44100 gt snap To r 00h00 m00 s7 00h00 m00 The fs rate is selected in the Project Rate box in the lower left corner The microphone volume is near the top of the window for setting the recording volume To prepare for audio recording select Edit gt Preferences A window as shown below will appear r _ Audacity Preferences r a Audio 1 0 Quaity File Formats Spectrograms Directories Interface Keyboard Mouse r Playback Device Microsoft Sound Mapper Output Recording Device Microphone High Definition Aud v Channels 2 Stereo Play other tracks while recording new one Software Playthrough Play new track while recording it Under Audio I O set Channels to Stereo and Device to Microphone High Definition Audio Device to select the external microphone and not the one built in to the camera Under Quality set Default Sample Format to 16 bit and then select OK Under File Formats you will choose whether you are saving nbits 8 or nbits 16 For 8 bit set Uncompressed Export Format
12. nnel 1 quantized voltage values in volts and column 3 has the 10 000 scope channel 2 quantized voltage values also in volts To import the saved scope waveform samples of the triangle wave which are in Excel format into the Matlab environment use the on line Matlab HELP resource to investigate the use of the built in Matlab function xlsread Note that you may need to designate which Excel sheet number to import if you saved several scope acquisitions covering multiple pages in one Excel file The xlsread function will convert the 3 columns of an Excel formatted file into a Matlab compatible array of dimension 10 000 x 3 floating point values Once the digitized waveform data is imported into Matlab all of Matlab s graphics capabilities are available to generate high quality labeled figures Use online help to investigate the built in plotting function stairs This plotting function creates a stair step plotted result appropriate for representing quantized waveforms Using stairs create two Matlab plots of the same waveform as quantized on channel 1 versus that of channel 2 Which channel reconstructs the triangular waveform with greater fidelity less observable stair steps How many levels can you see in the channel 1 waveform plot versus the number that you can see in the channel 2 plot What does this suggest should be the practice in terms of the number of graticules that a waveform occupies when capturing digitized waveforms by the pr
13. ocedure of this section if one wishes to pre serve the highest waveform fidelity 5 2 Dual Stereo Audio Signal Acquisition Obtain a microphone assembly with attached line cable from your lab TA Plug the line cable into the MIC jack on the front of the lab PC consult the on line Dell PC user guide for location Place the microphone assembly on the lab bench in a convenient close position to record your voice You will use the open source application Audacity to acquire a few seconds of dual channel audio from this assembly As in the case of the case of the scope waveform acquisition you control the fidelity of the audio waveform acquisition by adjusting three parameters the signal sampling rate temporal quantization in Hz the number of bits amplitude quantization and the volume level the gain control analogous to selecting the vertical waveform height adjustment on the scope The microphones have a roughly 10 KHz response range so a sampling rate of at least 20 KHz would be needed to fully capture all the frequency range of the microphones However most speech nominally falls under 5 KHz in frequency content For this task you will evaluate the quality fidelity of stereo audio recordings made for the following parameter selections using PCM pulse code modulation audio format 1 fs 22050 Hz nbits 16 volume full fs 22050 Hz nbits 16 volume half fs 22050 Hz nbits 8 volume full gt a WwW N fs 11025 Hz nb
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