ReverbSc and quiet signals

Troubleshooting and Support
1

I am trying to add reverb to my primitive synth. After borrowing some code from the MultiEffect sample, everything sounded great for most of my samples. However, a number of my samples are quiet and when dry/wet is set to anything more than 0.2, nothing is heard once the reverb takes place.

I am wondering if there is some sort of gate in the ReverbSc algorithm that prevents signals under some threshold to be processed. A few fragments from my rather pedestrian code:

void AudioCallback(AudioHandle::InputBuffer  in,
                   AudioHandle::OutputBuffer out,
                   size_t                    size)
{
    pod.ProcessDigitalControls();
    ProcessButtons();

    for(size_t i = 0; i < size; i++)
    {
        float outl   = 0;
        float outr   = 0;
        float signal = synth.Process();

        GetReverbSample(outl, outr, signal, signal);
        OUT_L[i] = outl;
        OUT_R[i] = outr;
    }
}

void GetReverbSample(float &outl, float &outr, float inl, float inr)
{
    float drywet = midiEngine.GetDryWet();
    rev.Process(inl, inr, &outl, &outr);
    outl = drywet * outl + (1 - drywet) * inl;
    outr = drywet * outr + (1 - drywet) * inr;
}

   float sample_rate = pod.AudioSampleRate();
    rev.Init(sample_rate);

    //reverb parameters
    rev.SetLpFreq(18000.0f);
    rev.SetFeedback(0.85f);

The dry/wet parameter is controlled via MIDI CC and its value is between 0 and 1.0f.

I also check the source code of the reverb and it looks the problem may be related to a gain constant set to a magic value (below).

static const float kOutputGain = 0.35;

Thanks

2

Reading over the code, it doesn’t look like there’s any noise gating. kOutputGain is an interesting catch though. I’m guessing the reverb gets quite loud with hot signals, and needs a constant gain to knock it down at the end.

One thing you could test is just adding a multiplier of 2x or 3x to the wet signal before you output it. Something like

outl = 3 * drywet * outl + (1 - drywet) * inl;

Test that with a quiet signal. If you can hear the reverb a lot better, than that’s the issue. That being said, that wouldn’t be the permanent fix. You’d probably need some kind of compressor situation to boost the reverb with quiet signals, but not let it clip with loud signals.

If the constant gain doesn’t work the issue may be something else. Let me know how that goes!

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