Processing audio in stereo in processBlock

Audio Plugins
1

Hi all,

I am experiencing a problem where I only get audio from the right channel. This is my code is processBlock, what am i doing wrong here? I am trying to process a custom filter in stereo, meaning left and right channel.

for (int channel = 0; channel < buffer.getNumChannels(); ++channel)
{
float* channelData = buffer.getWritePointer (channel);

  Filter* highPassFilter = (channel == 0) ? &leftHighPass : &rightHighPass;

  for (int sample = 0; sample < numSamples; ++sample)
  {
       channelData[sample] = highPassFilter-process(channelData[sample]);

       leftHighPass.setHighPass(getSampleRate(), highPass);
       rightHighPass.setHighPass(getSampleRate(), highPass);
   }

}

Your assistance would be appreciated as always.

2

Ok, looking at my code I think another issue with my code is that I’m setting the parameters inside the loop, would that be the reason? I will move them out of the loop and see if the problem persist. But in the mean time any other suggestions are welcomed.

1 Like
3

I would keep it simple and just create two instances of the filter class, one per channel, as private members of our processor

myFilterClass hpf[2];

then, in your processBlock

for(int c = 0; c < numChannels; ++c)
{
  for(int i = 0; i < numSamples; ++i)
  {
    channelData[i] = hpf[c].process(channelData[i]);
  }
}
4

Thank you @lcapozzi for your response, yeah that would be the simplest way of doing it but i was right the problem was caused by setting the parameters inside the loop, i moved it outside the loop and it worked.

5

you can update filters in a loop. the way you did it just felt a little confusing. cause you still had that step of selecting a filter while aleady being in the loop, which is kinda redundant. if you used an array of filters, like ica suggested, it could look like this:

for(int c = 0; c < numChannels; ++c)
{
  auto channelData = buffer.getWritePointer(c);
  hpf[c].setHighPass(getSampleRate(), highPass);
  for(int i = 0; i < numSamples; ++i)
  {
    channelData[i] = hpf[c].process(channelData[i]);
  }
}
6

@Mrugalla I appreciate your input. Upon reviewing my code more closely, I realized that while setting filter parameters inside the channel loop indeed works, my initial error was setting them within the sample loop. By moving the parameter-setting operations outside of the sample loop and into the channel loop, I was able to resolve the issues and ensure proper processing of stereo audio with the desired filter settings. Thank you for your assistance in troubleshooting this matter.