1.1 Matlab Recording & Analysis Program
Contents
1. on the upper plot in the GUI window In addition to the time domain waveform a spectrogram is computed using Matlab s built in specgram function part of the signal processing toolbox An example recording of the sentence We were away a year ago is shown below Lovage me l il Fiil Flay Esk Lim Zrin ka Zam I Taras 56 Fraqeerecy kr Tire ac We were away a year ago Zooming in on the Waveform One can examine a region of interest in the waveform using the Zoom in button When Zoom in is clicked the cursor will change to a cross hair Clicking the left mouse button and dragging a rectangle around the region of interest in the time domain waveform will select a sub section of data In the example below we have zoomed in on the region from about to 1 2 seconds Lyh a Hj i a Fiiil Fay Esk Lami Trian Be Foon Ma i x yy l ih h hh i M IW i ih ali N s i h Ny I M y gl Von a LN Vy 4 Le p E Zoomed in on the waveform Zooming out The Zoom out button will change the axis back to what it was before Zoom in was used If you zoom in multiple times zooming out will return you to the previous axis limits Listening to the Waveform The Play button uses Matlab s souna function to play back send to the speakers the waveform that appears in the GUI If you have zoomed in on a particular section of the waveform only that2. 1 1 Matlab Recording amp Analysis Program Here we will present a Matlab program Record originally written by the author in the summer of 2001 and updated occasionally since The program is intended to simplify the recording and basic editing of speech waveforms as well as to present the spectrogram and the time waveform in a side by side format for ease of analysis Getting Started Before you can do any recording through Record you will need to connect a microphone or other sound source to the microphone input on your sound card The next step is to ensure that your computer is set up to record from the microphone On a Windows machine you must select the microphone as the source in the Record Control window see illustration below The Record Control window can usually be accessed from a speaker icon in the system tray Record Control Gptons Help CD Audio Bein lidigrsehane ekesdiae MIDI Balance Balance Balance Balance Balance Yolume eh Volume Volume Volume Volume ale E m role E Select T Select IW Select T Select T Select Advanced SB Live Mimer DF ou Microphone selected as the recording source Windows Sound Recorder program can be used to verify that the microphone is configured correctly If sounds can be recorded using this program they can also be recorded in Matlab If you can t record sounds there is some problem with the configuration i Sound Sound Rec Me x File Edit
3. Effects Help Positions Length 2 25 SEC 60 00 sec Windows Sound Recorder in action The remainder of this manual will describe the Matlab Record program its inner working and functionality Running the program The program can be run by typing record at the Matlab prompt or by opening the program in the Matlab editor and selecting Run from the Debug menu Recoraing Sound recording is initiated through the Matlab graphical user interface GUI by clicking on the record button The duration of the recording can be adjusted to be anywhere from to 6 seconds These are the GUI defaults but the code can be modified to record for longer durations if desired File Edit View Inset Tools Window Help Length 2 sec Be ee Upon being clicked the record button executes a function that reads in mono data from the microphone jack on the sound card and stores it a Matlab vector Most of the important information in a typical voice waveform is found below a frequency of about 4 kHz Accordingly we should sample at a least twice this frequency or 8 kHz Note that all sound cards have a built in pre filter to limit the effects of aliasing Since there is at least some valuable information above 4 kHz the Record GUI has a default sampling rate of 16 kHz however the waveforms portrayed in this document were sampled at 11 025 kHz Once recorded the time data is normalized to maximum amplitude of 0 99 and displayed
4. portion of the waveform will be sent to the speakers Saving and Loading Data Save is used to write the waveform to a wave file If zoomed in on segment of data only that portion of the waveform will be saved Click Load to import any mono wave file into the Record GUI for analysis Record Program Jesse Hansen hansenj ele uri edu
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