doubt regarding sampling frequencies I have a speech file that was recorded with a sampling frequency of 8kHz. I read the file in Matlab as [x,fs,nbits]=wavread('speech.wav). Now I play the file in Matlab using soundsc(x,fs). But if I use the command soundsc(x,fs/2) and soundsc(x,2*fs) the speech changes. What is the reason?
The soundsc command will playback $f_s$ samples per second. Playing back at a faster rate than you recorded will increase the pitch of the speech. Playing back at a lower sample rate will reduce the pitch. 

If you prefer to think in the frequency domain; all the information is scaled on the frequency axis with relation to the change in $f_s$. Reducing fs squashes the information on the frequency axis and increasing $f_s$ will stretch the information on the frequency axis.