[linux-audio-user] Fwd: [Jamin] Re: soft clip: Achieving Gain, inconsequential overloads

[Paul Winkler]

On Tue, May 04, 2004 at 10:57:21AM -0700, Mark Knecht wrote:
> > Suppose someone turns up the volume for more harmonics.  
> 
> But what harmonics? Where do these come from, and why? 

The kind of brick-wall limiting and gain-stage-hammering that
people do to get "loud" mixes introduces significant harmonic
distortion. That's "where".  I can't tell you "what", I don't
know the characteristics of the distortion technically.
As for "why"...

> If I record a
> violin correctly, why do people think they need more harmonics?

Wrong choice of instrument ;-)  Classical engineers tend to 
lean toward neutrality and accuracy in their recordings.

Now, proceeding as if you'd said "guitar" or "drums" ... ;-)
I have a (completely untested) theory that part of the reason is
due to the distortions that happen in the ear at high listening
levels (mentioned earlier in this thread).  
At rock-band volume, your ear adds harmonics and
maybe even does some kind of dynamics compression (it seems that
way to me, though I've not heard anyone else mention this effect).
Record the audio with a highly accurate, low-distortion system,
play back that same audio at home listening levels, and it literally does 
not sound the same. It sounds "smaller", not just quieter. 
This may be due to the absence of the harmonics created in the ear
by the very high level of the original.

So, some deliberate harmonic distortion is used to counteract
this effect, and make the music subjectively "big" even at low volume.

> Just a
> strange hearing thing that tends to favor having them? Possible, but
> also possibly black magic. I guess I'm too 'old school'! ;-)

I suppose you use only measurement microphones too ;-)

Really it's nothing new. Plenty of "old school" pop/rock/blues/etc 
engineers pushed their analog tape and analog consoles hard to get some
soft clipping, which both introduces harmonics and acts as a sort
of peak limiter.
Now we're still doing much the same thing, only we're using
high-tech brick-wall limiters. 

I suspect those old-school pop engineers discovered tape saturation
and related techniques somewhat by accident. Nobody thought it out
ahead of time, they just noticed  it made some records stand out from 
the crowd, maybe carry a bit better on AM radio, and the next thing you 
know your kids are watching "duck-and-cover" films in school. Oh wait, 
that was a different arms race ;-)
 
-- 

Paul Winkler
http://www.slinkp.com