Digital System Processing (Audio Processing)

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Lina Ngoopos
Lina Ngoopos 2020-12-9
评论： Lina Ngoopos 2020-12-9
I'm working on project to find the piano notes of a song. From the time domain graph, I was able to find the correct frequency where the note is present. I used: [S,F,T] = spectrogram (y, 512 , [] , 512, fs); to get the frequency of my song. But the size of the matrix S is too big and I cannot find the correcr frequency row. Can someone please help me understand how to get the correct row of frequency knowing the time?
Thanks
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Mathieu NOE
Mathieu NOE 2020-12-9
hello
do you have a audio (wav) file to share ?
Lina Ngoopos
Lina Ngoopos 2020-12-9
Hello! Unfortunately, the audio that I have is the format .m4a, I cannot attached it. My problem is understanding how to extract the frequency from the spectrogram array knowing the time. Is there a way you can explan this to me without me sending the audio? You can use any .wav files you can have. It is the concept that I'm trying to understand

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Elimelech Schreiber
编辑：Elimelech Schreiber 2020-12-9
If you have a specific time, then you should probably find the maximum frequency at that time, in the matrix S.
Each column in the matrix S contains the magnitudes of all the processed frequencies at a certain timestep.
e.g. Lets say t=1.13[sec].
first find the correct time index in T, which index 'i' yields T[i] =~ t (= 1.13) :
[~, i ] = min(abs(T - t))
lets say you've found i = 11,
now find the INDEX of the maximum magnitude in the i-th column of S:
[~, maxIdx] = max(S(:, i) ) % S(:, i)- The i-th column, containing freq. magnitudes at timestep i
finaly convert that index into a frequency, using F:
maxFrequency = F[maxIdx];
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Elimelech Schreiber
Elimelech Schreiber 2020-12-9
Yes, replace it if you have already found it.
And skip that step: that line is meant to find the correct index.

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