Hi,
So, there must be quite a lot going on in Focusrite's Liquid Channel.
http://global.focusrite.com/mic-pres-channel-strips/liquid-channel
Reputedly Focusrite license a system from Sintefex.
http://www.sintefex.com/docs/appnotes/dynaconv.PDF
Ciao,
Dave Hunt
Date: Mon, 20 May 2013 20:33:33 +0000
From: Fons Adriaensen <f...@linuxaudio.org>
On Sun, May 19, 2013 at 10:18:35AM +0200, J?rn Nettingsmeier wrote:
On 05/02/2013 01:26 AM, Richard Dobson wrote:
I have always understood it to mean that the behaviour is not
dependent
upon ~when~ the signal is injected. Thus, a plain delay is TI
because
everything is always delayed the same way; while a modulated
effect such
as a flanger (maybe using a variable delay) is not TI as exactly
what
comes out depends in the time something goes in.
...
for practical purposes, i guess fons' definition is more useful,
because then the term "LTI" system is strictly limited to something
that can be fully described with an impulse response.
Despite what I wrote before, I tend to agree with Richard. If I
interpret
his formulation correctly, a system is time-invariant iff, when the
output
for input x(t) is y(t), then the output for x(t + T) is y(t + T),
for any
T. It's actually quite difficult to formulate a stronger version
*unless*
you assume that the system is linear as well.
A linear time-invariant (LTI) system is fully defined by an impulse
response, or by a transfer function in the frequency domain.
Now consider three cases:
1. A filter,
2. A tremolo effect,
3. A compressor.
The filter is LTI, while the tremolo and compressor are not. Do they
fail to be LTI because they are not linear, or because they are not
time-invariant ?
The tremolo fails Richard's TI criterion. But it *is* linear in a
very strong sense: for any a(t) and b(t) Tremolo (a(t) + b(t)) ==
Tremolo (a(t)) + Tremolo (b(t)).
The compressor is time-invariant according to Richard's criterion.
But it isn't linear in the way the tremolo is. It could be said to
be linear 'at any instant', assuming attack and release times are
non-zero. But that is a somewhat problematic definition of linearity,
since apart from trivial cases (pure gain) linear processes depend
on the input's or output's history, and are not defined by some
relation at a single instant.
So it seems that a stronger definition of TI is not necesssary.
Ciao,
--
FA
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)
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