crossFilt causing Matlab audio plugin pops

Audio plugin splits incoming audio into three bands and applies gain to center band and sums all back together. Debugging by only writing out one band, continuous pop noise still occurs. Is this because the crossover filter should be done with a different method in the App?

When I do this process offline in a normal m file there is no distortion.

classdef test_process < audioPlugin

properties

LowBand = 500;

HighBand = 5000;

fs = 48000;

gain = 0;

end

properties (Constant)

PluginInterface = audioPluginInterface( ...

audioPluginParameter('LowBand','Label','Hz','Mapping',{'lin',70,1000}),...

audioPluginParameter('HighBand','Label','Hz','Mapping',{'lin',2000,10000}),...

audioPluginParameter('gain','Label','dB','Mapping',{'lin',0,20}));

end

methods

function out = process(plugin,in)

%set up crossover filter

crossFilt = crossoverFilter( ...

NumCrossovers=2, ...

CrossoverFrequencies=[plugin.LowBand,plugin.HighBand], ...

CrossoverSlopes=12, ...

SampleRate=plugin.fs);

[m1,m2,m3] = crossFilt(in); % split into three bands

%normal operation commented out for debug

% midGain = m2*(db2mag(plugin.gain)); % apply gain to mid band

% out = m1+midGain+m3; % sum three bands

%Test without any sum

out = m2; % test just mid band

end

end

end

Answer 1

[jibrahim]

Hi Matthew,

the main problem here is that you are recreating the corssover filter for every incoming frame of audio. Instead, you should create it once, in the contructor, in order to preserve the internal filter state.

You should also use getSampleRate to get the value of the plugin's sample rate instead of maintaning it as a property.

Here is a new version.

classdef test_process < audioPlugin            
    properties
        LowBand = 500;
        HighBand = 5000;
        gain = 0;
    end
    properties (Constant)
        PluginInterface = audioPluginInterface( ...           
            audioPluginParameter('LowBand','Label','Hz','Mapping',{'lin',70,1000}),...
            audioPluginParameter('HighBand','Label','Hz','Mapping',{'lin',2000,10000}),...
            audioPluginParameter('gain','Label','dB','Mapping',{'lin',0,20}));
    end

    properties (Access=protected)
        crossFilt
    end

    methods

        function plugin = test_process
            %set up crossover filter
            plugin.crossFilt = crossoverFilter( ...
                NumCrossovers=2, ...
                CrossoverFrequencies=[plugin.LowBand,plugin.HighBand], ...
                CrossoverSlopes=12, ...
                SampleRate=getSampleRate(plugin));
        end

        function out = process(plugin,in)                    
            %set up crossover filter
         
                [m1,m2,m3] = plugin.crossFilt(in);  % split into three bands
                
                %normal operation commented out for debug
                % midGain = m2*(db2mag(plugin.gain)); % apply gain to mid band
                % out = m1+midGain+m3; % sum three bands
                %Test without any sum
                out = m1+m2+m3; % test just mid band
        end

        function set.LowBand(plugin,val)
            plugin.crossFilt.CrossoverFrequencies(1) = val;%#ok
            plugin.LowBand = val;
        end

        function set.HighBand(plugin,val)
            plugin.crossFilt.CrossoverFrequencies(2) = val;%#ok
             plugin.HighBand = val;
        end

    end
end

[Matthew Worker]

This solution works. Originally initializing the filter every frame is the root cause of the issue.

Thank you!