Is it posible to set 2 inputs in audio plugin?

I am designing a spectral subtracter to evaluate losses in perceptual audio coding, which consists in a plugin that compares the audio spectrum of two signals, the original and the compressed one. The thing is that i want to develop this code as an audio plugin but i am having some troubles to set two different inputs in my plugin, as the process function only has one in, right? Is there any way of adding another extra input? Or any idea to avoid having this problem?

Thank you.

Answer 1

[jibrahim]

Hi David,

It is possible to design plugins with more than one input. Here is a simple example:

classdef myPlugin < audioPlugin

    properties (Constant)
        PluginInterface = audioPluginInterface( ...
            audioPluginParameter('scale','DisplayName','Scale','Label','','Mapping',{'lin',0,1}),...
            'InputChannels',[2  2], ...
            'PluginName','myPlugin' ...
            )
    end

    properties
        scale = .1
    end

    methods
        function y = process(obj,x1,x2)
            y = obj.scale*x1+x2;
        end
    end
end

Validation and generation of the plugin should work:

validateAudioPlugin myPlugin
generateAudioPlugin myPlugin

If you were to use the generated plugin in MATLAB, you would have to concatenate the two inputs. For example:

hostedPlugin = loadAudioPlugin("myPlugin.dll")
y = process(hostedPlugin,randn(1024,4));

[David Montalbán Caamaño]

Thank you for your reply, is there anyway of testing the plugin in the audio test bench? Because when i try to run it, it says that there are not enough inputs.

[jibrahim]

Hi David,

That is a limitation of audio test bench: Plugins with more than one input are not supported.

There are two workarounds that might help you:

1) Instead of writing a plugin that requires two inputs, use just one input, and concatenate the two input signals into one multi-channel signal.

2) Use audio test bench with a supported example plugin (e.g. audiopluginexample.Echo), set the testbench with your desired input/output settings, and then click the 'Generate Script' to generate a MATLAB script containing code equivalent to the testbench setup. You can then modify that code with your desired plugin, and insert your second input manually.

[David Montalbán Caamaño]

Hi @jibrahim,

Thank you for your support, I have one last question. I want the plugin to be able to load two different files, one mp3 file with the compressed signal and another wav file with the original one, as they are these two inputs I mentioned previously, as any file loader of any software that allows you to navigate through the explorer. ¿Is this posible? ¿How can I implement this in the code of my plugin?

Thank you so much.

[Gabriele Bunkheila]

Hi David,

I wasn't sure what you meant with your latest question but I'll try a couple of ideas to help us identify exactly what you are after.

From your MATLAB code (e.g. an edited version of the code generated byAudio Test Bench), you could use a file-selection utility such as uigetfile with 'MultiSelect','on'. Then read both separately with two different dsp.AudioDeviceReader objects. In the loop, read the samples from both objects separately in the loop and feed the frames of samples read by each as inputs to your plugin within the streaming loop.

dir = fullfile(matlabroot,'toolbox','audio','samples');
filenames = uigetfile({'*.mp3;*.wav'}, [], dir,'MultiSelect','on');

% Create test bench input and output
fileReader1 = dsp.AudioFileReader('Filename',filenames{1}, 'PlayCount',10);
fileReader2 = dsp.AudioFileReader('Filename',filenames{2}, 'PlayCount',10);
assert(isequal(fileReader1.SampleRate,fileReader2.SampleRate))

player = audioDeviceWriter(fileReader1.SampleRate);

% Create the objects under test
sut1 = myPlugin;
setSampleRate(sut1,fileReader1.SampleRate);

% Open parameter tuners for interactive tuning during simulation
tuner1 = parameterTuner(sut1);
drawnow

% Stream processing loop
while ~isDone(fileReader1) && ~isDone(fileReader2)
    % Read from input, process, and write to output
    in1 = fileReader1();
    in2 = fileReader2();
    
    out1 = process(sut1,in1,in2);
    
    player(sum(out1,2))
    
    % Process parameterTuner callbacks
    drawnow limitrate
end

% Clean up
release(fileReader1)
release(fileReader2)

Note that file reading always takes place outside the boundaries. The code outside the plugin here needs to care cared of some of the tasks normally taken care of by a DAW, e.g. ensuring the two sample rates match, and that samples are always availability from both files.

If you prefer a workflow fully based on interactive Apps, you could also turn your MATLAB plugin into a binary VST or AU plugin (from Audio Test Bench or via generateAudioPlugin), then use it from your DAW of choice, and handle file selection and signal routing directly from the DAW.

I hope this helps.