Leveller effect adds distortion

[kozikowski]

Yes, that's pretty much what a hard limiter does.

Again dipping into ancient history, the CBS Labs company made a two-box audio processor that was once found in every FM station in the US. Volumax and Audimax. In hardware, they did what Chris does, except they didn't have look-ahead. The Audimax was the graceful overall volume setter and the Volumax would whack off the peaks that could give you an illegal radio signal.

The Audimax had a meter on the front that gently drifted up and down to follow the overall loudness of the show. The Volumax had a peak reading meter that vibrated like you stuck your finger in the electrical socket. It was a hard limiter and it did what leveler does -- almost right down to the waveforms.

Koz

[steve]

The Leveller effect differs from a hard limiter in that there is just one threshold and that is the "noise floor" setting (default -70dB). ALL waveforms above this threshold are distorted to a lesser or greater extent according to their amplitude. As Koz has described in the previous message, a hard limiter only affects peaks that exceed a high level threshold.

[kozikowski]

Wellllll. OK, but it's a fine line difference. You can adjust a Volumax down and Leveler up and get precisely the same effect.

Koz

[steve]

Yes, or at least something very similar.

In contrast, the leveller produces a huge amount of harmonic distortion. This effect has more in common with "soft clipping" than it does with "dynamic compression" (in the traditional sense).

But as Bill pointed out, the "standard" (default) settings are significantly different to what an engineer would normally expect from soft clipping;

As for "soft clipping", I don't think that's a good analogy, especially since Leveller is changing the values of samples well below the clipping level.

If you plugged in your Volumax and it created noticeable distortion on all of the audio signal, your first thought would probably be that it was faulty. (then you would probably start cursing the idiot that left the Volumax with the threshold turned all the way down to -70dB)

Unfortunately the Leveller effect can not easily be used as a soft clipping limiter because the highest available threshold is -20dB which is much lower than one would normally use for soft clipping. Also, the distortion that it produces on low level signals is not the same kind of distortion as is produced with high level signals.
The picture bellow shows what happens to a low level sine wave when the Leveller effect is applied. The upper track is the sine wave before processing and the lower track is after applying the leveller. The vertical zoom level is at maximum.

tracks000.png (20.54 KiB) Viewed 1317 times

[steve]

In case anyone is interested - here is a simple plug-in for "soft clipping".
Yes it produces distortion - soft clipping does that.

For experimental purposes, values outside of the default ranges may be used by typing directly into the boxes rather than using the sliders.

WARNING. Processing long tracks with this effect in Audacity 1.3.9 may cause a crash due to a memory issue in Nyquist. Memory usage is not optimised in this plug-in, but I have processed a 45 minute stereo track using Audacity 1.3.10 (alpha) without any problem. Audacity's memory usage went up to about 450MB during processing of this long track, but dropped back down to normal when processing was complete. There should be no problems with shorter tracks.

softclip.ny.zip

Soft Clipping effect. Extract the contents into the Audacity Plug-ins folder.

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