Subject: Re: ADAT clicks (was:[linux-audio-dev] munlock and mmap)
From: David Olofson (david_AT_gardena.net)
Date: Thu Apr 06 2000 - 07:21:34 EEST
On Wed, 05 Apr 2000, Niklas Werner wrote:
> Hi there!
>
>
> > I haven't yet figured out (or checked) if the Alesis ADATs click, but
> > I doubt it. I don't know know how they would avoid this. If they have
> > an analog input signal, oh, sure ... they just put an analog delay in
> > the path of tape monitor outs, and then when they switch back and
> > forth between monitor in/monitor out, the digital signal from the tape
> > is in sync with the delayed-analog signal. But this would imply that
> > the analog signal is always delayed, which seems unlikely.
>
> Well, ADATs don't click as a matter of fact. proTools doesn't click as
> well! (at least I didn't have any clicks in my studio).
> Maybe this is due to having it implemented in DSPs, instead of
> "allround"-chips ???
This makes no difference except that you can cut latency from some
3-5 ms down to around one sample + whatever delay there is in the
converters and analog cirquitry.
Oh, AFAIK, ProTools has more than 3 ms latency anyway, BTW. I don't
know if this applies to *all* signal processing, but it pretty much
has to affect anything that you can route through a plugin. Not even
DSPs are efficient enough to run plugins one sample at a time and
still get a sane price/performance ratio.
> There isn't a delay in the analog signal as you rightly guessed.
>
> If you have digital input you can punchinout as well without clicks
> (well, I'm in the fortunate position of having a gigantic digital console
> to work on ;-) that does all the converting and syncing).
Digital vs. analog are only different interfaces, as long as we're
not dealing with true analog bypass. The latency is higher for the
analog I/O, but you'll get that latency in the external converters
instead, if you use the digital I/O. Involving a digital console very
likely adds some more latency.
Note: I'm talking about latencies in the ms range - nothing that any
normal person would notice as a delay under normal conditions.
> sounds like a hairy thing to solve, but:
> As far as I know proTools is the only DAW that doesn't (at least not
> audibly) click while punching inout. All the other native versions do
> click! and nobody really cares, as long as it doesn't click in the final
> recording!
Well, that's no excuse, really... Eventually, people will expect
native systems to be truly useful for serious recording, and start to
expect a more solid impression. Clicks sound cheap.
Anyway, as long as the signal passes through the dsp code, there
logically *has to* be some way of eliminating the click. Of course,
the latency of the mixer thread + audio driver, card etc will delay
the start time of the crossfade (or whatever is done). Also, the
fact that the input->output latency and the mixer->output latency
are two different things has to be taken in account. You can never
get below the former if the input signal is to be mixed in.
//David
.- M u C o S --------------------------------. .- David Olofson ------.
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