Subject: Re: [linux-audio-dev] LADSPA problem
From: David Olofson (david_AT_gardena.net)
Date: Sat Oct 28 2000 - 08:33:49 EEST
On Mon, 23 Oct 2000, Steve Harris wrote:
[...]
> > To me, the latter makes a lot more sense, as that's what happens in
> > analog systems. Also, one of the major advantages of using floating
> > point data is just that you get rid of the restricted dynamic range
> > of integer data. This makes things a lot easier inside the DSP loops,
> > and I really think this advantage should serve the user as well, by
> > letting entire plugin nets operate along the same principles.
>
> I agree that floats are convienient for plugins, and, in a lot of cases the
> plugin can do its stuff without caring what the amplitude of the signal
> is, but not always.
Of course, and you'll just have to deal with it in similar ways as
you do with analog hardware. The good part is that there are various
ways that software could help automate some of that. :-)
[...]
> As you can work with low and overload signals in floats without much
> loss, why not just propose -1/+1 (or whatever) as the nominal 0dB, and
> and allow pre/post gain control to prevent fx nets clipping? Many fx will
> work fine with any input anyway, and those that don't can be trimmed so
> they get sane imput levels. That's more or less what you do in hardware.
> Hell, this is computer land, you can just shove in an amp plugin if you
> need to trim.
Yep!
BTW, nets containing level sensitive plugins are usually designed to
actively deal with signal levels - that's what they're all about!
Other nets shouldn't be bothered with any 0 dB levels or anything,
as that would only make it harder to get the to do whet they're meant
to do.
> > > What are you supposed to do? The limiter I looked at works by asking
> > > for the threshold (in arbitary units), but this isn't a very good
> > > solution.
> >
> > How about dB?
>
> Yeah, but relative to what?
The apparently still non-existent default 0 dB level! :-)
> If you built a limiter which assumes and
> asks for +-1, and it's getting +-16000, your limiter setting will be
> +80dB odd, that's confusing.
Yeah, that's why a standard 0 dB level is needed. Most plugins won't
be affected, while others (and some hosts) will have to keep
amplitudes in the same order of magnitude (hosts: scale data as
required), rather than multiplying with some arbitrary value.
> > Or how about just saying that -1.0 .. 1.0 is the desired 0 dB
> > amplitude of signals? This doesn't restrict anyone from using a
> > completely different range, but it would make things a lot easier for
> > users.
>
> That would be good, might be better to use the AES(? or is it SMPTE)
> standard for analogue 0dB. That way the float programs will be fine
> (no resolution loss) and the int packages will have plenty of
> headroom. Gives compressors and limiters traditionaly meaningful values.
>
> IIRC 0dB analogue was decided to be -18dB dbFS, a bit low for my liking,
> but hey, in 24bit land it probably doesn't matter, and you can always
> drive into the "red" if you're in 16 bit.
>
> That would make the "you're not supposed to clip" input range +-3 if I
> did my arithmetic right, which sounds a bit odd, but when you say +-1 is
> 0db, and you have 18dB of headroom, it makes more sense.
That sounds nice; basically an additional reference 0 dB level,
that's slightly more similar to a hard clip level, while still being
only a recommendation to make plugin interaction comprehensible to
users. It would be (kind of) ok if some plugins clipped at the +18 dB
level, but any plugin that clips in undesired ways at the 0 dB level
is broken.
//David
.- M u C o S -------------------------. .- David Olofson --------.
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