SampleRateConvertion error in plugin

Hi

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.

Br

Pablo

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

Answer 1

[Jimmy Lapierre]

Hi Pablo,

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

[Pablo Panitta]

HI Jimmy

Thanks a lot for your promt answer and detail explanation.

I cannot see how the process porposed is solving the issue. My understanding is the following: when plugin is instantiated in a DAW session, works at the sample rate of the session. As this is not knowing in advance by plugin, there´s no way to predefine the ‘InitialSampleRate’ parameter value (until inserted). So the methodology should be: insert the plugin in a session, get the its sample rate value, and then set up the InitialSamplerate accordingly.

But when I try to implement this concept, in the constructor areas (as always do with SystemObject parameter definition), it is not possible to define anything but fixed values (what is exactly I don´t need!). If I try to make it relative to samplerate of the plugin a “non tunable parameter…” error describe above appears.

E.g if your example is inserted in a 88kHz DAW session, the SampleRateConverter will end up working with initialSampleRate of 48kHz instead 88kHz?

If I'm wrong please let me know, otherwise : is there any way to do it?

Thanks

Pablo

[Jimmy Lapierre]

Hi Pablo, I should have gave some background information. Aa sample rate converter does not need to know the absolute sample rates, only the ratio between the output and the input. If your output/input ratio is contant (4), you can specify 48k input and 4*48k output. It will have the same effect if the sample rate turns out to be 44100 (it will upsample by 4 to 4*44100). Let me know if this helps!

[Pablo Panitta]

Hi

So, InputSampleRate & OutputSamplerate are taken only for xfactor, not for the actual values to be sampled. Great this solved my issue!

Just final question, I think this concept also applies to others system Object for oversampling (eg IIRHalfbandDecimator or IIRHalfbandDecimator) with the only difference that oversampling factor is fixed to 2 on those ones,right?

Thanks Jimmy

Pablo

[Jimmy Lapierre]

For your use-case, same concept. The SampleRate property is used either for display purposes or because these objects are also supported in Simulink, where they must propagate the sample rate.

For example, when resampling a digital signal x2, the same code that does 48k=>96k could do 96k=>192k (except that the latter could have a more lax filter design if you prefer, because of the limits of hearing).

[Pablo Panitta]

thanks Jimmy

[Adrian Alexander]

Hi i realy like the oversampling code.

I want to change the code to some other oversamplingfactor like x8 or x16

what would change in the second part ? i dont realy know how it works.

ut = 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

thanks

[Jimmy Lapierre]

Replace all the "4*" by a constant named "OSF" (oversampling factor) and set it to 4, 8 or 16.