VST Code generation issues with element-wise multiplication

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Robert
Robert 2022-11-11
评论： Jimmy Lapierre 2022-11-11
The following code produces audible discontinuities when compiled to a VST:
gains = [0.5, 0.725];
out = in .* gains;
But this works fine
gains = [0.5, 0.725];
out = [in(:,1) * gains(1), in(:,2) * gains(2)];
Is this a known issue with code generation?

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回答（1 个）

VBBV
VBBV 2022-11-11
Ran in:
gains = [0.5, 0.725];
in = rand(8)
in = 8×8
0.8849 0.9486 0.2943 0.5330 0.5551 0.2483 0.9058 0.8506 0.6508 0.8914 0.3171 0.4493 0.6775 0.0840 0.3678 0.6322 0.2078 0.4190 0.9428 0.2469 0.3487 0.5543 0.0761 0.7525 0.8023 0.4535 0.7250 0.9433 0.3312 0.5522 0.5628 0.8056 0.2804 0.6671 0.6911 0.2097 0.8895 0.6512 0.3580 0.4607 0.2275 0.3705 0.9019 0.3368 0.4651 0.0667 0.7093 0.3143 0.8744 0.2188 0.9651 0.2883 0.7966 0.2366 0.2595 0.6238 0.6302 0.3316 0.5598 0.3719 0.0362 0.0559 0.2016 0.5517
out = [in(:,1) * gains(1), in(:,2) * gains(2)]
out = 8×2
0.4425 0.6877 0.3254 0.6463 0.1039 0.3038 0.4011 0.3288 0.1402 0.4837 0.1137 0.2686 0.4372 0.1587 0.3151 0.2404
out = in .* gains % check the matrix multiplication rule
Arrays have incompatible sizes for this operation.
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Robert
Robert 2022-11-11
Ran in:
Thanks for the quick response. I agree with this, but the default VST is 2 in, 2 out. This code should work if that were true:
gains = [0.5, 0.75];
in = [ones(5,1), ones(5,1)*2];
out = in .* gains
out = 5×2
0.5000 1.5000 0.5000 1.5000 0.5000 1.5000 0.5000 1.5000 0.5000 1.5000
Is it possible that the VST doesn't always default to stereo like the documentation says?
"By default, both the input to and output from the process method have two channels (columns). The number of input rows (frame size) passed to process is determined by the environment in which it is run. The output must have the same number of rows as the input.", found here:
https://www.mathworks.com/help/audio/gs/audio-plugins-in-matlab.html
Jimmy Lapierre
Jimmy Lapierre 2022-11-11
I was able to reproduce the issue. I will investigate further.
>> p=loadAudioPlugin('GainTest.dll')
p =
VST plugin 'GainTest' 2 in, 2 out
>> process(p,ones(4,2))
ans =
0.5000 0.7250
1.0000 1.0000
1.0000 1.0000
1.0000 1.0000
Please use the workaround in the meantime.
p.s. modifying the input in-place is allowed, so it could look like this:
function x = process(~,x)
gains = [0.5, 0.725];
x(:,1) = gains(1)*x(:,1);
x(:,2) = gains(2)*x(:,2);
end

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