How can I change the sampling frequency of audio signal?

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nada fady
nada fady 2015-6-13
回答： Ayush Bhandarkar 2023-1-25
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 .

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采纳的回答

Walter Roberson
Walter Roberson 2015-6-13
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()
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madhushankar BS
madhushankar BS 2020-12-4
But the number of samples is not reducing if we are halving the sampling frequency. Why?
Walter Roberson
Walter Roberson 2020-12-4
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.

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更多回答（2 个）

Azzi Abdelmalek
Azzi Abdelmalek 2015-6-13
[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);
  1 个评论
nada fady
nada fady 2015-6-13
编辑：nada fady 2015-6-13
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?

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Ayush Bhandarkar
Ayush Bhandarkar 2023-1-25
I guess this should work,
[y,fs] = audioread(filename);
left = (:,1);
fs2 = fs/2;
fs3 = fs*2;
% soundsc(left,fs2);
soundsc(left,fs3);

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