Hi Fareed.
To create a spectrogram plot for the audio file, the “spectrogram” function in the Signal Processing Toolbox is recommended to be used instead of the “imwrite” function. You can refer to the following documentation to learn more about creating spectrogram plots of audio files:
The “spectrogram” function plots the audio spectrogram along with a colormap for the power spectral density. It also returns a variable “s” containing the “Short-Time Fourier Transform” (STFT) data for the audio signal. The “stft” function also returns this variable without the spectrogram plot. You can learn more about the “stft” function in the following documentation:
The STFT data obtained from either of the above two functions can be passed as input to the “stftmag2sig” function to reconstruct the audio file. You can run the following code to understand how this can be done:
% Read audio file
[y,Fs]=audioread('audio2.wav');
% Input Arguments for spectrogram function
wind = hamming(128);
olen = 64;
nfft = 1024;
% Storing the STFT data in variable "sy" using "spectrogram"
[sy,fy,ty] = spectrogram(y,wind,olen,nfft,[],[],Fs,'centered','power','yaxis');
% Storing the STFT data in variable "sy" using "stft"
%[sy,fy,ty]=stft(y,Fs,'Window',wind,'OverlapLength',olen,'FFTLength',nfft);
% Plotting the spectrogram:
spectrogram(y,wind,olen,nfft,[],[],Fs,'centered','power','yaxis');
% Reconstructing the audio signal from STFT data:
ybar = stftmag2sig(abs(sy),nfft,Fs,'Window',wind,'OverlapLength',olen);
%To hear the original audio sound
% sound(y,Fs);
% To hear reconstructed audio
sound(ybar,Fs);
Minor changes do occur to the reconstructed audio in “ybar” compared to the original audio “y”, as the “spectrogram” or “stft” function attenuates the signal towards the edge of the window and effectively removes some of the energy of the signal. I hope this helps with the issue.
