Subject: Re: [linux-audio-dev] LADSPA 64bit FP support ?
From: David Olofson (david_AT_gardena.net)
Date: Sun Mar 26 2000 - 02:32:33 EET
On Sat, 25 Mar 2000, James McCartney wrote:
> on 3/25/00 12:59 PM, David Olofson at david_AT_gardena.net wrote:
>
> > the mantissa is
> > actually 25 bits, including the one's bit that's an implied 1 in
> > non-denormals
>
> No, its 24. 1 sign bit, 8 exponent bits, 23 mantissa bits plus the one
> implied.
Doh! Of course... :-)
> >> 16 bits is already sufficient if it were just SNR.
> >
> > No, not unless it's dynamic. Ever heard a CD fade out when playing it
> > back at above 100 dB peak?
>
> CDs dont have 16 bits SNR at all amplitudes. That's my point.
Ok, I thought "16 bits mastered and ready to go" for some reason.
Obviously, there is no SNR problem if the actual signal peaks at 16
bits...
> > But what happens if you add a very high amplitude signal to an audio
> > signal (to make some other plugin modulate the audio signal for
> > example), and then filter that signal away. What happens to the
> > mantissa?
>
> I'd say you are making a mathematical mistake if you are formulating your
> calculations in such a way.
It's not for the programmer to decide. It's perfectly possible to set
up something like that by connecting some plugins in any plugin
system. If it makes sense is a matter of artistical freedom rather
than system design and coding. As for non-audio signals, it's not at
all acceptable to assume that a low amplitude signal will not be
mixed with another higher amplitude signal, that will be removed in
the processing. Whether these problems occur within or between
plugins is just a matter of how fine-grained the plugin set is.
> > Two different definitions of "dynamic range":
> >
> > 1) The difference between the minimum signal level that can
> > be registeged, and the clip level.
>
> correct.
>
> > 2) The resolution of a sample at the peak level.
>
> This is signal to noise ratio, not dynamic range.
Well, that's what I meant; the general audio equipment confusion
mentioned...
> >> With FP the dyanamic range doesn't depend on the amplitude for
> >> any practical purpose.
> >
> > Depends on what you call a "practical purpose". (See above.)
>
> Wrong. For FP dynamic range does not depend on amplitude, unless you have a
> denormalized number, period.
Addition and subtraction of FP numbers means that bits will be lost
unless the exponents are equal.
Now, specify what a user may and may not do with plugins without
losing bits.
//David
.- M u C o S --------------------------------. .- David Olofson ------.
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