AFC/AFCPlugin.m at main · OliverRasmussen/AFC · GitHub

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classdef AFCPlugin < audioPlugin
   % AFC  Adaptive Feedback Cancellation plugin

   properties
      InputGain = 0;
      FilterOrder = 64;
      StepSize = 0.001;
      FilterCoefficients = zeros(2^13, 1); % (Max order = 8192)
   end
   properties (Access = private)
      FilterInput = zeros(2^13, 1); % Input buffer for adaptive filter
      PreviousInput = zeros(2^15, 1); % Previous input samples (reference signal)
      Epsilon = 1e-5; % Small constant to avoid division by zero
   end
   properties (Constant)
      PluginInterface = audioPluginInterface( ...
         'PluginName', 'Adaptive Feedback Canceller', ...
         'VendorName', 'AudioGoodizer Inc', ...
         'VendorVersion', '1.0.0', ...
         'UniqueId', '2a0Y', ...
         'InputChannels', 1, ...
         'OutputChannels', 1, ...
         audioPluginParameter('InputGain', ...
            'DisplayName', 'Input gain', ...
            'Label', 'dB', ...
            'Mapping', {'pow', 1/3, -96, 12}, ...
            'Style', 'rotary'), ...
         audioPluginParameter('FilterOrder', ...
            'DisplayName', 'Filter Order', ...
            'Mapping', {'int', 64, 2^13}, ...
            'Style', 'rotary'), ...
         audioPluginParameter('StepSize', ...
            'DisplayName', 'Step Size', ...
            'Mapping', {'lin', 0.001, 1.0}, ...
            'Style', 'rotary'));
   end

   methods
      function set.FilterOrder(plugin, value)
         plugin.FilterOrder = value;
         plugin.FilterCoefficients = zeros(value, 1);
         plugin.FilterInput = zeros(value, 1);
      end

      function set.StepSize(plugin, value)
         plugin.StepSize = value;
      end

      function reset(plugin)
         plugin.FilterCoefficients = zeros(plugin.FilterOrder, 1);
         plugin.FilterInput = zeros(plugin.FilterOrder, 1);
         plugin.PreviousInput = zeros(2^15, 1);
      end

      function out = process(plugin, in)
         in = in * 10^(plugin.InputGain/20); % Apply gain to input signal
         inBlockSize = length(in); % Get input block size
         out = zeros(inBlockSize, 1); % Preallocate output block
         prevBlock = plugin.PreviousInput(1:inBlockSize); % Get previous input block (reference signal)
         plugin.PreviousInput(1:inBlockSize) = in; % Store current input block for next iteration

         % Process each sample in the block
         for n = 1:inBlockSize
            % Get sample from previous block
            x_n = prevBlock(n);

            % Add sample to filter input
            plugin.FilterInput = [x_n; plugin.FilterInput(1:end-1)];

            % Estimate the feedback signal
            y_hat = plugin.FilterCoefficients' * plugin.FilterInput;

            % Calculate error signal
            e_n = in(n) - y_hat;

            % Update filter coefficients (NLMS rule)
            normFactor = (plugin.FilterInput' * plugin.FilterInput) + plugin.Epsilon;

            plugin.FilterCoefficients = plugin.FilterCoefficients + ...
               (plugin.StepSize / normFactor) * plugin.FilterInput * e_n;

            % Update output block
            out(n) = e_n;
         end

         % Normalize output block if clipping occurs
         if (max(abs(out)) > 1)
            out = out / max(abs(out));
         end
      end
   end
end