How can I change the sampling frequency of audio signal?

Hi,

I am working on a speech recognition , and am aiming to change the sampling frequency of the audio signal. I wrote the following code :

clear y Fs

%Read the data to the MATLAB using audioread.

[y,fs] = audioread(filename);

%Play the audio.

sound(y,fs);

%change the sampling rate

fs2= fs/2;

audiowrite(filename)

%Read the data back into MATLAB using audioread.

[y,fs2] = audioread(filename);

sound(y,fs2);

when I run it I heard the sound twice in different FS together, But the problem is the original sound has been changed because I wrote on it (audiowrite (filename)).

So can some one help me to change the Fs without changing the original one and compare the results by sound instruction and plot instruction .

Answer 1

[Walter Roberson]

audiowrite(filename) is going to fail because you must provide at least 3 parameters to audiowrite: filename, samples, and output frequency.

If you do not want to overwrite the original file then supply a different file name. For example,

newfile = tempname();
audiowrite(newfile, y, fs2);

If all you are going to do with it is read it back in again, then it is pointless to do so: you are just going to get y and fs2 back again. audiowrite() does not resample the data: it just writes the frequency in the header, and whatever tool you use to play the sound is responsible for taking care of the frequency. For example,

sound(y, fs);
sound(y, fs/2);

You probably want resample(), or fft() then ifft(), or interp1()

[nada fady]

thank you very much ...your answer helps me a lot

please can you help me to use fft() and change delta f and then use ifft() ???

[Walter Roberson]

Example :

ifft(fft(x), 2*length(x))

[nada fady]

thaaaaanx alot

[LearningMatLab]

So for newfile = tempfile() , where ,and what, would we put for this specific example ?

[Walter Roberson]

tempfile() is not part of MATLAB, but tempname() is.

newfile = tempname();

Is a complete valid line of code. It tells MATLAB to generate a name of a temporary file in a directory appropriate for storying temporary files. It does not create the file, just returns a valid name for a file. You might perhaps want to use

newfile = [tempname(), '.wav'];

This would be for the case where you need to create a file to work with, but you do not need the file to be stored permanently.

[madhushankar BS]

But the number of samples is not reducing if we are halving the sampling frequency. Why?

[Walter Roberson]

madhushankar BS :

There are a few different things that people sometimes want to do:

• keep the samples exactly the same, but change the frequency. For example, slowing down a recording of a person who is talking fast to make it easier to understand. This involves keeping the samples the same but telling the hardware to use a different frequency; the amount of time the signal pertains to changes
• drop or interpolate samples, to try to construct what the signal would have been like if it had lasted the same amount of time but had been recorded at a different sample rate; resample() is a good tool for that
• raise or lower the "key" someone is singing or talking at, "pitch conversion", "autotune". This can involve interpolating samples and changing the frequency.

Answer 2

[Azzi Abdelmalek]

[y,fs] = audioread(filename);
%change the sampling rate
fs2= 2*fs/3;
audiowrite(filename,y,fs2)
%Read the data back into MATLAB using audioread.
[y,fs2] = audioread(filename);
sound(y,fs2);

[nada fady]

Thank you Azzi Abdelmalek to replay

I wrote exactly the same code, but , as i mentioned above the original sound has been changed . is there a way to keep both frequencies and compare them? and how can i plot them?

Answer 3

[Ayush Bhandarkar]

I guess this should work,

[y,fs] = audioread(filename);

left = (:,1);

fs2 = fs/2;

fs3 = fs*2;

% soundsc(left,fs2);

soundsc(left,fs3);