How to use audioDeviceWriter ?

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)

Answer 1

[Jimmy Lapierre]

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.

[Dora Kokai]

Thank you for helping!I tried it out and i got error like:

Error using zeros

Size vector should be a row vector with real elements.

[Walter Roberson]

Just use

    audiowriter(y(:));

[Walter Roberson]

Your g is a scalar coming out of your function.