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PEQ Bug Causing Clipping (or at least causing JRiver to report Clipping)

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mattkhan:
I will be surprised if this effect is the root cause here, I thought pretty large magnitude peaks were being reported?

mwillems:

--- Quote from: mattkhan on August 14, 2015, 02:07:21 pm ---I will be surprised if this effect is the root cause here, I thought pretty large magnitude peaks were being reported?

--- End quote ---

I'm seeing less than a dB or so, sometimes a little more in my testing.  I think Hendrik's answer is probably the answer.  The attenuation of a second order butterworth high pass at 40Hz isn't much, but the phase shift casts a long shadow.  A dB (or even 2) is well within the range of what phase summing (or reduced cancellation) could possible cause.

The nature of the effect would make it invisible to most types of measurement (single tone sine waves, pink noise, or swept tones wouldn't show this effect, you need actual program material or multitone sine waves).

There may be an issue here, but the filters are performing correctly when measured, so I'm not sure how they could be boosting the signal other than in the way Hendrik described (i.e. why wouldn't it show up in a sine sweep)?

mattkhan:
I thought Lisbeth was talking about -10dB on a channel basis but +1dB clipping? Perhaps I misinterpreted but that seems way out of line for this effect.

mwillems:

--- Quote from: mattkhan on August 14, 2015, 02:22:37 pm ---I thought Lisbeth was talking about -10dB on a channel basis but +1dB clipping? Perhaps I misinterpreted but that seems way out of line for this effect.

--- End quote ---

If that's what she's seeing I agree, that's out of the realm of this effect.  I don't think this effect could cause more than 6dB of gain in perfect storm conditions.

There's definitely a discrepancy between what analyzer is reporting and what the clip detector is reporting.  But as between the two I think analyzer is probably wrong. For example I was using some program material with a peak near 0db and R128 dynamic range of less than 2dB(!) and watching the clip meter.  It was clipping like crazy under the test conditions (which is what you'd expect), but the total overage was always less than 150% (usually closer to 120%).  Analyzer's RMS level was all over the place (plus or minus 5dB) during this even when there were no meaningful perceptual changes in volume.

mattkhan:
I have done limited testing recently on this sort of thing (the effect of minimum vs linear vs composite filters on a signal) and the effect is really about deformation of the waveform rather than serious level changes.

 i could be wrong of course :) I think she needs to provide a sample track to rule out a bug though. I need to find that bug report I mentioned in the thread, that came from someone who really knows his stuff so would be inclined to trust him.

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