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Topic: Does the "Advanced Limiter" work at all? (Read 1166 times) previous topic - next topic
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Does the "Advanced Limiter" work at all?

Hi guys,

I have a heavily clipping test file. In the converter I set up a profile with just the Advanced Limiter in the dsp chain. Nothing else is done, no dithering, no replaygain application. Source and target is flac.

Replaygain calculated track peak remains the same: 2.57

Truepeak scanner analyses the clipped samples. The difference between source and target files is negligible. Clipping all over the place.

Is there a misunderstanding on my end? That would be my guess. From all I read, and there is a detailed explanation from Kode54 here in the forum, I was expecting AL to bring down peaks to ~0.99, maybe minus some intersample issues.

Source file:
X

Target file:
X

Track: https://exophobiaorgqebrus.bandcamp.com/track/--14

Tested a few more files with less clipping. Replaygain peaks will always remain the same between source and target.

Re: Does the "Advanced Limiter" work at all?

Reply #1 –
limiters can not fix already clipped samples.
limiters only try to avoid clipped samples when used in DSP chains and when sample format is in floating point, so samples can be out of clipped range, which is typically [-1, 1]

Re: Does the "Advanced Limiter" work at all?

Reply #2 –
Quote from: fooball on
Quote from: Squeller on
So that would bring down the clipping samples which are messed up anyway... but preserve the gain stage, right?
If the input is already clipped there's no way to restore it.  What (I think) is under discussion is samples over full scale which are the direct result of resampling (when the interpolated waveform exceeds FS).  With FB2K working floating point internally, there is no clipping as the result of resampling, but could be when the output is converted to fixed point.  And that's where the limiter comes into play.
In other words: the limiter prevents the output clipping as a result of internal processing, the limiter does not (and cannot) correct for input that is already clipped.
It's your privilege to disagree, but that doesn't make you right and me wrong.

Re: Does the "Advanced Limiter" work at all?

Reply #3 –
"when used in DSP chains and when sample format is in floating point" - yep, should have thought about it for a longer moment. Thx guys, it's now clear :-)

Re: Does the "Advanced Limiter" work at all?

Reply #4 –
Just to add that @fooball replied correctly in the other thread that Advanced Limiter deals with the PCM data. It makes sure the PCM samples don't exceed allowed digital range as that would cause hard clipping. It doesn't do anything to intersample peaks. Early versions of the Advanced Limiter touched lossless sources, samples hitting maximum legal values caused limiter to get triggered. That was later fixed. Now a file that can be losslessly stored in integer PCM won't be altered at all. As your FLAC source is in integer PCM it will pass through the limiter bit-perfectly.

Note that high intersample peak clipping can be audible under extreme circumstances. Reducing loudness of an entire track so that such intersample peaks are below digital fullscale would definitely be audible.

You didn't ask, but Advanced Limiter's limiter is designed to be audibly transparent. It sees incoming clipping in advance and starts reducing loudness of that part smoothly so nothing will get clipped. After clipping is averted original playback amplitude is smoothly restored.