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How to use audioDeviceWriter ?

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Dora Kokai
Dora Kokai on 23 Nov 2020
Edited: Dora Kokai on 28 Nov 2020
I would like to use a compressor/expander and I get the following message:
Error using audioDeviceWriter/setup
The number of input channels must be less than or equal to 255.
Error in audioDeviceWriter/setupImpl
Error in gyak (line 29)
audiowriter(y); - Show complete stack trace
The compressor's code is from the dafx book and i would like to see the result in timescope.
function[y,g] = compexp(x)
CT=0.00016;
CS=1;
ET=2.6;
ES=5;
tav = 0.01;
at = 0.03;
rt = 0.003;
delay = 150;
xrms = 0;
g = 1;
buffer = zeros(1,delay);
for n = 1:length(x)
xrms = (1-tav) * xrms + tav * x(n)^2;
X = 10*log10(xrms);
G = min([0, CS*(CT-X), ES*(ET-X)]);
f = 10^(G/20);
if f < g
coeff = at;
else
coeff = rt;
end
g = (1-coeff) * g + coeff * f;
y(n) = g * buffer(end);
buffer = [x(n) buffer(1:end-1)];
end
end
%using
frameLength = 1024;
audioreader= dsp.AudioFileReader( ...
'Filename','mintaa.wav', ...
'SamplesPerFrame',frameLength);
audiowriter = audioDeviceWriter( ...
'SampleRate',audioreader.SampleRate);
scope = timescope( ...
'SampleRate',audioreader.SampleRate, ...
'TimeSpanOverrunAction','Scroll', ...
'TimeSpanSource','property',...
'TimeSpan',1, ...
'BufferLength',44100*4, ...
'YLimits',[-1 1], ...
'ShowGrid',true, ...
'LayoutDimensions',[2,1], ...
'NumInputPorts',2, ...
'ShowLegend',true, ...
'Title',['Original vs. Compressed Audio (top)' ...
' and Compressor Gain in dB (bottom)']);
while ~isDone(audioreader)
x = audioreader();
y = compexp(x);
audiowriter(y);
x1 = x(:,1);
y1 = y(:,1);
scope([x1,y1]);
end
release(audioreader)
release(compexp)
release(audiowriter)
release(scope)

Answers (1)

Jimmy Lapierre
Jimmy Lapierre on 24 Nov 2020
I suspect that compexp returns a row vector instead of a column vector, so it looks like 1024 channels. Try pre-allocating y before your loop in compexp (i.e. y = zeros(x)) so that it's a column like x.
  3 Comments
Walter Roberson
Walter Roberson on 26 Nov 2020
Your g is a scalar coming out of your function.

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