[LAD] (Modular) Synth and Clipping

Dominique Michel dominique.michel at vtxnet.ch
Sat Jun 15 18:50:39 UTC 2013

Le Sat, 15 Jun 2013 14:56:13 +0100,
Aurélien Leblond <blablack at gmail.com> a écrit :

> Hi all,
> In a tentative of giving more personality to the modular synth modules
> of the avw.lv2 set, I have been looking at clipping.
> I would like here to discuss here a few assumptions, the fruit of my
> research and get a few feedback/comments to decide what direction to
> take.
> - in some cases (or let say modules of a synth), clipping is
> implemented more to copie what an analogue system would do than a
> mandatory part of the algorithm... Let's take an example: 2 sin waves
> mixed together of amplitude -1/1 will just have an amplitude of -2/2
> (as long as they are in phase)... A digital mixer without clipping
> would be able to cope with that, but an analogue one wouldn't... and
> that's why the analogue system would clip the signal......right?
> - What method of clipping is used will give a "personality" to the
> module: hard clipping, soft clipping, the method used for soft
> clipping, etc...right?
> - Hard clipping is something of the digital world - it doesn't exist
> in the analogue world... right?

As already pointed out, an analogue system with enough headroom won't
clip the signal. It is also almost impossible to generalize what will
append when an analogue system go in clipping. This will depend on what
kind of hardware this is (class A preamp, class A, AB or B amp, ...), on
what kind of feedback it use ("normal" audio amplifier with a lot of
feedback, or power "operational amplifier" in open loop like a guitar
amp, ...), on the technology in use (bipolar, j-fet, tubes, ...), on
the actual implementation of the whole thing inclusive its supply, and
even on the quality or power of the components in some cases.

As example, when you push guitar amps in clipping at full volume, half
of the clipping you can ear is, with some brands, not the clipping of
the electronic, but the clipping of the power transformer. That sounds
very bad -:(, and that imply you may have to change often this
transformer when such amps are used to play blues or rock like styles
of music. 

Even without going to such extreme cases, the actual implementation,
which is always a compromise between money and quality, will determine
the sound of any analogue system. And this is the most difficult part to
simulate -:)


> - Soft clipping will deform any waves of amplitude -1/1 even if it
> doesn't exceed the accepted threshold, because just before reaching
> the threshold  the algorithm will take over and softly make the signal
> reach the maximum amplitude and keep it there until the original
> signal goes back under a set threshold.....right?
> - Is there a preferred stage for clipping? In the case of a filter,
> should we clip before filtering, after or both? Or are all these
> options valid and that's what will give an additional personality to
> the filter?
> Thanks in advance for any comments!
> Aurélien
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