Peak Limiter / Expander

[vinylivo]

@steve

I’ve completed my “Soft Clipping Limiter” (attached).

@Gale Andrews

Well even Steve’s sounds distorted enough to my ears if I move the sliders far enough to left

This version is specifically for soft clipping and not “expansion”, so now moving the “ratio” slider to the right makes the clipping “harder”.
It also has an option to apply “make-up gain”. If make-up gain is enabled (default) then a peak output of +/- 1 before applying the effect will be clipped down (soft clipping) then boosted back up to +/- 1 (make-up gain).

In music production soft clipping is usually only done to catch occasional brief transients rather than lopping the top off everything. Much more than that and it will be clearly (and usually unpleasantly) audible with this type of effect. Of course, some may want to use the effect “creatively” to deliberately cause distortion. Setting a low threshold and a soft “hardness” setting can be used as a finely controllable “fuzz” effect.

Hi Steve, this is cool. A tool I already searched for a long time.
unfortunately edgar’s Broadcast Limiter has too much distortion for my taste when soft clipping is in action, some simple Tone test reveals this quite clearly in spectrum view. I always used the LADSPA ‘Declipper’ tool to do similar processing, but you can’t adjust anything (similar settings of steve’s ‘sclimiter’ will be threshold 0.8 and hardness 24). It is pretty clean - means it doesn’t generate too many high order harmonics - even slighly better than steve’s ‘Soft Clipping Limiter’. this is probably because the Declipper tool uses another function than exp, perhaps power to 2… Have to modify it and check generated harmonic contents.

Actually I’m not only interested for a nice soft clipper but more a Tape saturation plug-in. This can easily be accomplished by eqing before and after the clipping process. Therefore higher frequency signals are limited at a lower threshold than low freq signals and some of the generated higher harmonics get attenuated, this should help the sound. Have to try out, will come back after tests…

[slobjones]

I’m using Audacity 1.2.6 on a PowerPC Mac running Leopard.

I’ve installed the plugin, but when I define a section, select my peak settings and press OK, I get “Nyquist did not return audio.”

Anyone familiar with this error?

Thanks.

[steve]

@slobjones

I’m using Audacity 1.2.6 on a PowerPC Mac running Leopard.
I’ve installed the plugin, but when I define a section, select my peak settings and press OK, I get “Nyquist did not return audio.”

Audacity 1.2.6 is too old for the previously posted version of plug-in.

Attached to this post is a version that should be backward compatible with Audacity 1.2.6
(you’ll find that a lot of recent plug-ins don’t work with Audacity 1.2.6 as the 1.2.x series has not been updated for several years. I’d highly recommend upgrading to Audacity 1.3.13)
sclimiter.ny (1.86 KB)

[slobjones]

Many thanks, Steve. Just upgraded to the beta and found that all works well.

I’ll hang on to the backward-compatible version just in case!

I’m glad to discover this forum. I’m going to take another shot at Audacity, which has given me lots of trouble in the past. Still searching for a Mac app with the ease and simplicity of Goldwave for the PC.

Your plugin should be a big help.

[steve]

There is a minor bug in the previous version of the Soft Clipping Limiter plug-in. If the level of the final sample in the selection is high, then it may be amplified incorrectly and end up at a very high level. The bug is fixed in this version:
sclimiter.ny (1.9 KB)

[slobjones]

Thanks for the soft clipping limiter. I’ll try it out.

[steve]

@edgar-rft

Here is the new “Broadcast Limiter IV” using the Nyquist “shape” function. Funny: the audio processing is done in one single Nyquist function.

The “shape” part is based on Roger’s Distortion Tutorial.

The explanation of the “knee” math in the “coord” function is still missing (I’ve ripped it out of an electronics schematic diagram), it’s basically a logarithmic fade using “db-to-linear” to convert a linear “percent” relationship into a logarithmic volume change. I would like to find out how this can be expressed via “exp” and “log”, so we could write peakprocess function tables to get fully compatible “compress” and “expand” back and forth transformations.

I think there may be a slight error in the mathematics.
Changing the last line of the plug-in code to:

 (snd-from-array 0.0 *sound-srate* shape-array))

will output the wave-shaping curve.
Set the “knee” control to 3.0 and a distinct 0.1 dB step appears at the top of the curve, just as the curve becomes horizontal: