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Author Topic: Trying to understand Clip Protection in DSP  (Read 5507 times)

hulkss

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Trying to understand Clip Protection in DSP
« on: January 30, 2012, 12:54:33 am »

If a DSP operation pushes the audio signal into clipping and then another DSP operations pulls the level back down it seems that DSP clip protection does not see or report this type of problem. In my case, convolution is reducing the signal level before the digital volume control and clip protection shows low safe levels even though the signal clipped earlier in the DSP processing chain.

Many CD's are mixed so hot that there is inter-sample clipping if up-sampling is used. I have observed clipping on VST plug-in peak meters after up sampling in MC. It would be good if "volume leveling" could be applied before "output format" does any up sampling as "replay gain" is usually negative.

The peak level reported as a % by DSP "clip protection" should be watching the output level of each step in the DSP processing chain and reporting the maximum level. It seems to just report the level entering the last step which is digital volume.

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Matt

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Re: Clip protection not protecting or reporting peak DSP levels.
« Reply #1 on: January 30, 2012, 09:56:19 am »

Since all audio data is 64bit floating point, there's no hard limit at -1.0 and 1.0.

So if one effect does +100dB and the next effect does -100dB, no clipping occurs.

It's only a clip when that hard-limit between -1.0 and 1.0 is enforced before output (because it's required by the soundcard), and this is only at the very end.

So I think the current behavior is desirable and correct.
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Matt Ashland, JRiver Media Center

hulkss

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Trying to understand Clip Protection in DSP
« Reply #2 on: January 30, 2012, 11:15:19 pm »

Since all audio data is 64bit floating point, there's no hard limit at -1.0 and 1.0. So I think the current behavior is desirable and correct.

Good point. I was hoping all those extra bits and CPU load were good for something. So even though a VST plugin reports that the signal is clipping, that just means the signal is above 100% at that point in the DSP chain, no harm done?
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Matt

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Re: Trying to understand Clip Protection in DSP
« Reply #3 on: January 31, 2012, 08:39:45 am »

So even though a VST plugin reports that the signal is clipping, that just means the signal is above 100% at that point in the DSP chain, no harm done?

No harm done.

The only exception would be if the VST plugin itself did some sort of clipping between -1.0 and 1.0, but I wouldn't expect this.

JRiver's built-in DSP plugins do no extra clipping.  The only clipping is the final clipper / clip protection, and any changes it makes are reported in Audio Path.
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