How can I alter the speed of a wav file without altering its pitch?

I'm trying to be able to load a wav file, and either speed it up or slow it down. I've tried only changing the sampling frequency, but that changes the pitch of the signal. I find that the problem keeps becoming more and more complex as I go through to problem, so any help at all would be valuable. here's what I've attempted to do so far, but I only get static when I play back the file:

clear
[fName, pName] = uigetfile('*.wav');
[sig, fs, nbits] = wavread([pName fName]);
n = 2;  %speed by which file will be altered
for x = 2:(length(sig)-1);
  newFreq(x) = fs/(2*pi)*acos((sig(x+1)+sig(x-1))/(2*sig(x)));
  newFreq(length(sig)) = 0;
end
Fs = fs*n;
t = 0:1/Fs:(length(newFreq)-1)/Fs;
newSig = cos(2*pi*newFreq.*t);
size(newSig)
newerSig = transpose(newSig);
size(newerSig)
myAP = audioplayer(newSig,Fs);
playblocking(myAP);

[dpb]

What would speeding up or slowing down be other than changing pitch?

Not clear what you think you're trying to do here.

[Nick]

sorry, I'll try and be more clear. imagine that the file is a song that is the voice of someone singing. I want the song to sound the same, but I want it to be slower. When I only change the sampling frequency, the voice of the singer will get deeper and deeper as the sampling frequency gets lower, and I'm unsure of how to eliminate that effect.

[Bilal AKBANA]

Look at my answer clicking here

Answer 1

[dpb]

Oh, tempo-changing...tough nut to crack starting blindly...

http://www.dspdimension.com/admin/time-pitch-overview/

http://en.wikipedia.org/wiki/Audio_time-scale/pitch_modification#Phase_vocoder

Might check the File Exchange and see if there're any submissions on the subject.

Answer 2

[Brian Hemmat]

Typically, you would use a phase vocoder. The Pitch Shifting and Time Dilation Using a Phase Vocoder example in Audio Toolbox walks you through the algorithm.

Starting in R2019b, you can use the stretchAudio function or the audioTimeScaler object (for streaming).