Subject: Re: [linux-audio-dev] LADSPA 64bit FP support ?
From: David Olofson (david_AT_gardena.net)
Date: Wed Mar 22 2000 - 04:20:28 EET
On Wed, 22 Mar 2000, Alexander Ehlert wrote:
> Hi,
>
> > If you studied Calculus, you know how fast the precision can vanish,
> > when you have to deal with algorithms which show up some numerical
> > instability.
> >
> > Therefore for full 24bit audio quality the 32bit float is simply not enough.
>
> I think it's more a matter of good plugin design, when working with that
> sort of algorithms. You have to know the limits of your algorithm. And if
> you really need more performance you can still do conversion from float to
> double within the filter.
Yes, many VST (AFAIK) and DirectX plugins do this already. You'll
still garble the low bit of the float mantissa in the connections
between plugins, but it shouldn't go further than that in normal
cases...
> What are you going to do if you're reaching the
> limits of double precision and you want to have "full" 64bit quality?
That'll most probably never be a realistic requirement for audio, but
24 bits is already about to become a real limitation. If you need 20
real bits output, and you want to use 24 bit converters without
compressors or anything when recording percussion, you don't have all
that many bits to waste... The 24 bits of dynamics is really needed,
as you don't want to get the quantization noise inside the dynamic
range of the 20 bit output signal.
As an example that most of you have probably experienced; take
recording just about anything with a consumer 16 bit card. You have
something like 14 real bits, and 2 bits of "nice" analog noise. Now,
if you're recording at -6 dB (to be able to get any work done rather
than retaking for ages until you get -1 dB without clipping...), you
have 13 bits + 2 bits of "nice" noise. If you lose those two bits
to truncation in the processing, you have... well, nothing but crap
left. Even if you're just truncating noise away, you're audibly
degrading the signal.
//David
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