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Thread: AudioEffectFreeverbStereo - self-resonates with (internal) noise impulse?

  1. #1
    Junior Member
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    AudioEffectFreeverbStereo - self-resonates with (internal) noise impulse?

    With damping set to 0, I've had some very odd periodic noise impulse artefacts turning up in the output of FreeVerbStereo, even with the input at 0 volume over sustained periods.

    Anyway, i spotted something which might be irrelevant but seems to cure the issue when changed:

    In the last line of the for( loop in the update() function it has:

    outblockR->data[i] = sat16(outputL * 30, 0);

    Should this be:
    outblockR->data[i] = sat16(outputR * 30, 0);
    Instead?

    Otherwise it seems to throw most of the allpass filter calculations for the right output away?
    In any case, changing this cured my weird self-oscillation issue. I have no idea if it's an actual issue with the code or i've understood even less of what the Freeverb code is doing than I thought I did.

  2. #2
    Junior Member
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    Found the origin of the artefacts- I was feeding FreeverbStereo two channels instead of one- that overwrote one of the internal comb filter buffers silently and introduced a periodic noise. However, the original question still stands- is the right channel output buffer being populated from the wrong variable?

  3. #3
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    ...This leads to an interesting question from someone who knows nothing of audio (comms & measurement guy here). When one refers to "reverb", is the standard of practice to separate the channels with no cross mixing, or to allow cross mixing as might happen in a physical reverberating space?

  4. #4
    Quote Originally Posted by LenSamuelson View Post
    ...This leads to an interesting question from someone who knows nothing of audio (comms & measurement guy here). When one refers to "reverb", is the standard of practice to separate the channels with no cross mixing, or to allow cross mixing as might happen in a physical reverberating space?
    You do indeed cross mix reverbs. You often also use anti-phase additions to give the reverb extra width.

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