MATLAB: Distortion Plugin with variable Oversampling

audioAudio ToolboxdistortionDSP System ToolboxMATLABoversamplingpluginvariable

Hello i run into a problem here.
i got inspired for this way of aproatching oversampling by another question.
https://de.mathworks.com/matlabcentral/answers/658043-samplerateconvertion-error-in-plugin?s_tid=srchtitle
it is oversampling an Distortion Algorithm.
All i wanted to do is use the Code from the Question and let the user Pick the Amount of Oversampling desired ." oFactor = [1 2 4 8 16]"
Initialy i wanted to use enum mapping but as it didnt work i simplified the code . the int slider pickes one number of the oFator Array. That way i change the oversampling multiplicator.
The code works with a Constant property but not with one that can be changed. I dont know why.
thank u in advance 😉
Thats the Error i get:
Index in position 1 exceeds array bounds (must not exceed 4).
Error in PickOversampling2/stepImpl (line 70)
xin = disto(plugin.oFactor(plugin.oF)*ii-(plugin.oFactor(plugin.oF)-1):plugin.oFactor(plugin.oF)*endIdx,:);
Error in testbench_PickOversampling2 (line 69)
o1 = step(plugin, in(:,1:2));
Error in validateAudioPlugin
classdef (StrictDefaults)PickOversampling2 < matlab.System & audioPlugin
    
    properties (Constant)        
         oFactor = [1 2 4 6 16] ;
         
    end
    
    properties (Constant, Hidden)
         PluginInterface = audioPluginInterface(...
             audioPluginParameter('oF',...
             'DisplayName','oF',...
             'Label','dB',...
             'Mapping',{'int',1,5},...
             'Style', 'rotaryknob','Layout', [1 2])) 
    end    
    
    properties
        oF      = 1 
    end
    
    properties (Access = private)    
        Up16;
        Down16; 
    end
    
    methods
        % Constructor
        function plugin = PickOversampling2
  
            plugin.Up16=dsp.SampleRateConverter;
            plugin.Down16=dsp.SampleRateConverter;
            calculateSampleRates(plugin);
            
        end
        
    end
    methods(Access = protected)
        function out = stepImpl(plugin, in)
           
         x = step(plugin.Up16,in);  
         
         %Distortion
         
         Drive_lin = 100
         
          x = x * Drive_lin    ;
                     
          x(x>1)=1   ;
          x(x<(-1))=-1    ;
          
         disto=x;
                                     
          out = zeros(size(in));
         
         for ii = 1:4096:size(in,1)
         endIdx = min(ii+4095,size(in,1));
         xin = disto(plugin.oFactor(plugin.oF)*ii-(plugin.oFactor(plugin.oF)-1):plugin.oFactor(plugin.oF)*endIdx,:);
         assert(size(xin,1)<=plugin.oFactor(plugin.oF)*4096); 
         out(ii:endIdx,:) = step(plugin.Down16,xin);
         end
    
         end
     
        function resetImpl(plugin)
            reset(plugin.Up16);
            reset(plugin.Down16);
           
        end
        function calculateSampleRates(plugin)
          sampleRate = 44100; 
          plugin.Up16.InputSampleRate=sampleRate;
          plugin.Up16.OutputSampleRate=plugin.oFactor(plugin.oF)*sampleRate;
          plugin.Down16.InputSampleRate=plugin.oFactor(plugin.oF)*sampleRate;
          plugin.Down16.OutputSampleRate=sampleRate;
         end
        end
  
end

Best Answer

Hi Adrian,
There are multiple issues here.
First, to reproduce the error, execute this:
h = PickOversampling2
h.oF = 3
h(randn(4,2))
I haven't taken a close look at the code, but there seems to be an indexing error in the for loop. Note that plugins cannot make assumption on the input frame size or sample rate, so we test the plugin with different combinations of inputs sizes and sample rates when we validate it. You validate a plugin with validateAudioPlugin. You can use the -keeptestbench option to preserve a testbench MATLAB file you can run to reproduce and debug issues.
After you resolve this issue in your for loop, you will still have a problerm with your sample rate converters. These objects will not allow their input/output sample rates to be tunable. They must be contants for you to be able to generate a plugin. One solution is to instead use pairs of FIRInterpolator and FIRDecimator objects. Since you can't tune the decimation or interpolation factors, you need to predefine the objects and use the right one depending on the current value of your upsample factor.
This code should work. Note that I skipped the distortion part since it has issues to be resolved.
classdef (StrictDefaults)PickOversampling2 < matlab.System & audioPlugin
    properties
        OversampleFactor {mustBeMember(OversampleFactor,{'1','2','4','6','16'})} = '1'
    end
    properties (Access = protected)
        poF = 1;
    end
    properties (Constant, Hidden)
        PluginInterface = audioPluginInterface(...
            audioPluginParameter('OversampleFactor',...
            'DisplayName','Oversample Fsctor','Mapping',{'enum','1','2','4','6','16'}))
    end
    properties (Access = private)
        Up2;
        Down2;
        Up4;
        Down4;
        Up6;
        Down6;
        Up16;
        Down16;
        pBuff
    end
    methods
        % Constructor
        function plugin = PickOversampling2
            plugin.Up2 = dsp.FIRInterpolator(2,designMultirateFIR(2,1));
            plugin.Up4 = dsp.FIRInterpolator(4,designMultirateFIR(4,1));
            plugin.Up6 = dsp.FIRInterpolator(6,designMultirateFIR(6,1));
            plugin.Up16 = dsp.FIRInterpolator(16,designMultirateFIR(16,1));
            plugin.Down2 = dsp.FIRDecimator(2,designMultirateFIR(1,2));
            plugin.Down4 = dsp.FIRDecimator(4,designMultirateFIR(1,4));
            plugin.Down6 = dsp.FIRDecimator(6,designMultirateFIR(1,6));
            plugin.Down16 = dsp.FIRDecimator(16,designMultirateFIR(1,16));
            plugin.pBuff = dsp.AsyncBuffer('Capacity', 192000-1);
        end
        function set.OversampleFactor(plugin,val)
            plugin.OversampleFactor = val;
            switch val
                case {'2'}
                    plugin.poF = 2; %#ok




                case {'4'}
                    plugin.poF = 4; %#ok
                case {'6'}
                    plugin.poF = 6; %#ok
                case{'16'}
                    plugin.poF = 16; %#ok
                otherwise
                    plugin.poF = 1; %#ok
            end
        end
    end
    methods(Access = protected)
        function out = stepImpl(plugin, in)
            o = plugin.poF;
            switch o
                case {2}
                    x = plugin.Up2(in);
                case {4}
                    x = plugin.Up4(in);
                case {6}
                    x = plugin.Up6(in);
                case{16}
                    x = plugin.Up16(in);
                otherwise
                    x = in;
            end
            %Distortion
            % TO BE ADDED HERE
            % workaround the limitation of FIRDecimator (no unbounded
            % inputs allowed)
            write(plugin.pBuff, x(:,1:size(in,2)));
            FrameLength = size(in,1);
            z = read(plugin.pBuff, o*FrameLength);
            switch o
                case {2}
                    out = plugin.Down2(z);
                case {4}
                    out = plugin.Down4(z);
                case {6}
                    out = plugin.Down6(z);
                case{16}
                    out = plugin.Down16(z);
                otherwise
                    out = x;
            end
        end
        function resetImpl(plugin)
            reset(plugin.Up2);
            reset(plugin.Down2);
            reset(plugin.Up4);
            reset(plugin.Down4);
            reset(plugin.Up6);
            reset(plugin.Down6);
            reset(plugin.Up16);
            reset(plugin.Down16);
            reset(plugin.pBuff);
        end
    end
end
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