Asynchronous audio read with multiple channels in Matlab - matlab

Question

Hello wise people of the internet
My final goal is to create a code that shows a real-time spectrogram of 4-channel audio input device.
I have this code that can show spectrogram, but only after recording is complete:
clc; clear;
%~~~~~~~~~~~~~~~~~~~~~~~~
% Parameters
%~~~~~~~~~~~~~~~~~~~~~~~~
FileName2Save='mySpeech.wav';
NumChannels=2; % Number of recording channels
fs=44100; % Sampling Rate
Tw=50; Ts=10; % Parameters of Spectogram Framing: Tw = window Size [msec] | Ts = Windows steps [msec]
SessionTime=10; % Session Recording Time [Seconds] - After SessionTime The code stops sampling and plots spectogram
%~~~~~~~~~~~~~~~~~~~~~~~~
deviceReader=audioDeviceReader(fs, Tw*0.001*fs, "Driver","ASIO", "NumChannels", NumChannels);
setup(deviceReader)
disp('Recording Start')
All=[];
tic
% this bit is from the official documentation, showing how to get audio from 'audioDeviceReader'.
% In my opinion this is a really bad API design for Matlab.
while toc < SessionTime
acquiredAudio = deviceReader();
All=[All; acquiredAudio];
end
disp('Session Complete - Creating Spectogram')
% this bit is showing the spectrogram of the channels in a figure.
for iC=1:NumChannels
subplot(NumChannels,1,iC) % Change the image order as you like
spectrogram(All(:,iC),hann(round(Tw*0.001*fs)),round((Tw-Ts)*0.001*fs),20000, fs, 'yaxis', 'power');
drawnow
end
release(deviceReader)
disp('Recording complete')
I would like to show the spectrogram at real time while recording audio.
I tried couple of approaches:
1. To put the spectrogram command inside of the while.
This did not work because spectrogram command can take time, that make the while to not catch all of the samples.
2. Use parfeval command to run spectrogram in the background.
This did not work because the background thread can not do spectrogram. It also can't do simpler commands like disp.
I also tried afterEach with the parfeval but it makes the code that recieves the audio sample get stuck, and that's the same problem I mentioned earlier: If the code inside the while that receives samples gets stuck even a bit, we're losing samples here.
3. Use parfeval command to get the samples of the audio in the background.
I tried running the code that gets the audio in the background, and then use send command to get the new data and do spectrogram every time.
This did not work (see comment in code):
function GetSamples(q)
All = [];
tic;
while toc < 0.5
newValues = ...;
All = [All, newValues];
send(q, arr); % Goes to next only when spectrogram is complete drawing
end
end
The 'send' command calls the code that prints the spectrogram, and apparently only continues to the next in the while when the spectrogram drawing is complete, which can take a few seconds.
When the next values are queried, were losing a couple of samples here.
4. Use audiorecorder, which is asynchronous by default
Can't, because the requirement here is recording 4 channels at the same time.
If audiorecorder was able to record 4 channels, the problem will get solved because I could do something like:
record(recorder);
tic;
while toc < 5
y = getaudiodata(recorder);
spectogram(...);
drawnow;
end