Lab 1 – Matlab Basics

Goals:

·       Learn to record, save, and playback speech using Matlab.

·       Use Matlab to plot the speech waveform.

·       Learn the .wav file format.

·       Get started using Matlab arrays.

·       Listen to what you see.

 

Getting Started with Matlab

Double click on the Matlab icon.

When Matlab is open, there is always a command window.  That’s all you need for now.

 

Matlab online help is excellent.  There is no need for manuals.  The help includes tutorials.  I suggest you do at least the array tutorial (outside of class) if you have not worked with Matlab before.  Also learn how to use the editor and write and run a simple function.

 

Recording and Playing Sound

·       Make a recording of yourself saying “We were away a year ago.”

Make sure the microphone is on.

In the Matlab workspace window, type

      Fs = 10000;

            y = wavrecord(40000,Fs);

Hit return and after a slight pause (.5 second) say the sentence.

·       Play the sentence you just recorded.

      wavplay(y,Fs);

Now try

      wavplay(y,Fs/2);

and

      wavplay(y,Fs*2);

What happens?  You have just done your first Computer Speech Processing.

 

Saving and Loading Sound Files

wavwrite(y,Fs,'filename');      % creates a .wav file of the signal y.

signal = wavread('filename');  % reads in a signal from a .wav file.

[signal,Fs = wavread('filename');

            % reads in a signal and the recording frequency, Fs, from a .wav file.

Plot the Waveform

plot(y);                       

Then stretch the window so it runs from one side of the screen to the other.

My recording of  “We were away a year ago.” is shown here.

 

           

Find the range of values for y.  Type ‘max(y)’ and hit return with no ‘;’, same for min(y).

Now try mean(y).

Crop the Signal

You can see from the plot that there is a second of background noise at the start and end of my recording.

            z = y(10001:30000);   % Creates a 2 second signal with mostly speech

10001:30000 make the new signal exactly 2 seconds long but any length will do.

Save your cropped signal as ‘YIaway’, where ‘YI’ is replaced by your initials. 

 

Find the Words

·       Plot and stretch your cropped signal. 

·       Guess where you the word boundaries are.  There are 10000 samples to a second.

·       Use your guesses to create single-word signal arrays for each of the words

      ‘we’   ‘were’   ‘away’   ‘a’   ‘year’   ‘ago’

 

 

From the plot above, I guessed that the word “ago” would be in the array:

            ago=z(15500:20000);

But wavplay(ago,Fs); showed that I missed the start of the word.

            ago=z(15400:20000);

seems to get the whole word.

 

Rearrange the words

·       Rearrange your words to synthesize ‘a year away, were we ago?’  You can do this with:

·       wavplay(a,Fs);wavplay(year,Fs);wavplay(away,Fs);wavplay(were,Fs);wavplay(we,Fs);wavplay(ago,Fs);    % Type it all then hit return.

·       A better way:

      nonsense = cat(1, a, year, away, we, ago, were);

      wavplay(nonsense,Fs);

      Listen to the new sentence and describe its quality.  What seems wrong?

 

Some more Sentences

·       Record, crop, and save these two sentences:

      Should we chase those cowboys?       (YIcowboy)

      Early one morning a man and a woman ambled along a one mile lane. (YIlane)

·       Create words from “Should we chase those cowboys?”

·       Synthesize the sentence “Cowboys chase those we should.”

·       Synthesize the sentence “Cowboys should chase those away.”

Send me the files containing your three cropped recordings.  I will collect them and make them available so we can use them for further study.