Question
I´m trying to implement a x4 oversampling process but I´m having difficulties on how let the SampleRateConverter sytem object knows about sample rate used. When compiling the example attached for plugin generation, the following error shows up: “Failed to compute constant value for nontunable property 'SampleRate'. In code generation, nontunable properties can only be assigned constant values.” I'd really appreciate if someone can give me a hint on how fix/treat this. classdef (StrictDefaults)DistoLab_Test2 < matlab.System & audioPlugin properties GainDisto=0; Input=0; Volume=0; end properties (Constant, Hidden) % Define the plugin interface PluginInterface = audioPluginInterface( ... 'InputChannels',2,... 'OutputChannels',2,... 'PluginName','DistoLab_Test2',... audioPluginParameter('Volume', ... 'DisplayName', 'Out', ... 'DisplayNameLocation','none',... 'Label','dB', ... 'Mapping', { 'lin', -15, 15}, ... 'Style', 'rotaryknob', 'Layout', [4 6]),... audioPluginParameter('Input', ... 'DisplayName', 'In', ... 'DisplayNameLocation','none',... 'Label','dB', ... 'Mapping', { 'lin', -5, 5}, ... 'Style', 'rotaryknob', 'Layout', [4 3]),... audioPluginParameter('GainDisto', ... 'DisplayName', 'Saturation', ... 'DisplayNameLocation','none',... 'Style', 'rotaryknob', 'Layout', [4,5],... 'Mapping', { 'lin', 0, 10}, ... 'Filmstrip','knob_67_black.png', ... %<-- 'FilmstripFrameSize',[80,80]), ... audioPluginGridLayout('RowHeight', [30 90 10 100 37], ... 'ColumnWidth', [30 100 100 20 100 100 20 80 80 80 60], 'Padding', [10 10 10 10])); end properties (Access = private) Up4; Down4; end methods % Constructor function plugin = DistoLab_Test2 plugin.Up4=dsp.SampleRateConverter; plugin.Down4=dsp.SampleRateConverter; calculateSampleRates(plugin); end end methods(Access = protected) function out = stepImpl(plugin, in) inadjusted=in*(10^(plugin.Input/20)); % Incoming signal adjusted by Input Gain %SampleRateConverter x4 process v=step(plugin.Up4,inadjusted); disto=(v*plugin.GainDisto).^5; % input distorted outdisto=(disto)*(10^(plugin.Volume/20)); out = step(plugin.Down4,outdisto); end function resetImpl(plugin) reset(plugin.Up4); reset(plugin.Down4); end function calculateSampleRates(plugin) plugin.Up4.InputSampleRate=getSampleRate(plugin); plugin.Up4.OutputSampleRate=4*getSamplerate(plugin); plugin.Down4.InputSampleRate=4*getSampleRate(plugin); plugin.Down4.OutputSampleRate=getSampleRate(plugin); end end end
Expert Answer
Kshitij Singh
PhD Expert
Answered Aug 12, 2026
There are some limitations with codegen and the resampling objects. If you have a hard-coded ratio of 4, the easiest way around it might be to use a nominal sample rate, such as 48kHz. The added benefit is that avoid calls to getSampleRate will be faster.
function calculateSampleRates(plugin)
sampleRate = 48000; % use a nominal rate
plugin.Up4.InputSampleRate=sampleRate;
plugin.Up4.OutputSampleRate=4*sampleRate;
plugin.Down4.InputSampleRate=4*sampleRate;
plugin.Down4.OutputSampleRate=sampleRate;
end
The following challenge will be that the input of the sample rate converter will be of unknown size. You can get around that by looping over partitions of a maximum size (like 4096). Something like this might work for you:
% Replaces out = step(plugin.Down4,outdisto);
out = zeros(size(in));
for ii = 1:4096:size(in,1)
endIdx = min(ii+4095,size(in,1));
xin = outdisto(4*ii-3:4*endIdx,:);
assert(size(xin,1)<=4*4096); % Tell codegen xin won't be larger than 4x4096
out(ii:endIdx,:) = step(plugin.Down4,xin);
end
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