FW: AW: Re: digital contents

[Haible_Juergen#Tel2743]

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From: Haible_Juergen#Tel2743
To: Paolo Predonzani
Subject: AW: Re: digital contents
Date: Thursday, 19. September 1996 15:48


Wow, this is interesting stuff!

BTW, my mailer show that this mail goes only to me (no cc),
but I am sure that the DIY list in general and people like
Don  or Joachim would be very interested in this as well!

>The non-linearities are a major problem because they are present in
>every term of the (4th order) differential equation the filter obeys to.
>This makes the poles move in the s-plane for constant cutoff freq and Q.
>The small signal analysis shows 4 coincident poles in -p (open loop).
>The large signal analysis shows that the poles move between -p and the
>origin of the s-plane. The static open loop gain also varies.

This really caught my attention! So far I have only looked at the
nonlinearities as a cause of harmonics/distortion, and not shifting
poles as well! This would mean that the cuttof frequency changes
with signal input strength ...
Now, this makes me question: (1) How are "poles" defined for
large signal analysis? I only know this concept for linear circuits.
How are they defined for nonlinear circuits? Time domain
response for a certain input signal, and then inverse fourier
transform? If so, for which input signal ??
(2) How *far* would these poles move? Usually, the signal amplitude
thru the ladder is small in comparison with the bias current. (?)


> The typical computation time is 40sec for 10sec of music at 22050Hz on
> a 80486DX266.
> For the aliasing problem I use superresolution. Adaptive oversampling
> is used (much like in ray tracing).

I think people who say, that nonlinearities in Digital are much of a 
problem,
have real time processing in mind, where oversampling is more critical;
but you might  check this with Don Tillman - he is for sure the most
knoledgeable person I have found on the net. Digital implementation
is way over my head to say anything serious - but keep me on track
about these discussions as well!

Now for me, my main quest is to *understand* what exactly happens
in the original analogue circuits, so this stuff about large signal
analysis is very interesting to me - can't hear enough of it!
(Equations welcome (;->) )

Regards,

JH.

(I did not forward your letter to DIY because it was a private mail;
but if you want, I highly sugest that you forward both your mail and
my answer to DIY ! We need such discussion here!)