Sound Processing in MATLAB

In this semester, I am pursuing the subject, "Speech Processing". A real fascinating subject .  I also liked it in every manner as my B.Tech final year project was actually related to Speech Processing. ( See my previous blog posts) .




 A little try with the sound processing of  Matlab. Hope you will like it.

What is digital sound data?

Getting a pre-recorded sound files (digital sound data)

Click here to access a .wav file



Download any .wav file from here name it anything. In my case , let it be 'road.wav'

Loading Sound files into MATLAB

·        I want to read the digital sound data from the .wav file into an array in our MATLAB workspace.  I can then listen to it, plot it, manipulate, etc.  Use the following command at the MATLAB prompt:

[road,fs]=wavread('road.wav');

·       The array road now contains the stereo sound data and fs is the sampling frequency.  This data is sampled at the same rate as that on a music CD (fs=44,100 samples/second).

·       See the size of road:  

size(road)

·       The left and right channel signals are the two columns of the road array:

 left=road(:,1);

right=road(:,2);

·       Let’s plot the left data versus time.  Note that the plot will look solid because there are so many data points and the screen resolution can’t show them all.  This picture shows you where the signal is strong and weak over time.

time = (1/44100)*length(left);

t=linspace(0,time,length(left));

plot(t,left)xlabel('time (sec)');

ylabel('relative signal strength') 

·       Let’s plot a small portion so you can see some details

  

time=(1/44100)*2000;

t=linspace(0,time,2000);

plot(t,left(1:2000))

xlabel('time (sec)');

ylabel('relative signal strength')

 ·       Let’s listen to the data (plug in your headphones).  Click on the speaker icon in the lower right hand corner of your screen to adjust the volume.  Enter these commands below one at a time.  Wait until the sound stops from one command before you enter another sound command!

soundsc(left,fs)       % plays left channel as mono

soundsc(right,fs)    % plays right channel mono (sound nearly the same)

soundsc(road,fs)     % plays stereo