Subject: Re: [linux-audio-dev] LADSPA 64bit FP support ?
From: Paul Barton-Davis (pbd_AT_Op.Net)
Date: Wed Mar 22 2000 - 08:36:13 EET
>(Doubling and halving have no effect on the mantissa at all...?)
#define PEAK_VAL ~(0xff000000)
int32 foo;
float ffoo;
foo = PEAK_VAL;
foo *= 2;
foo /= 2;
if (foo != PEAK_VAL) {
fprintf (stderr, "Your C compiler or processor is broken\n");
}
ffoo = (float) PEAK_VAL;
ffoo *= 2.0;
ffoo /= 2.0;
if (ffoo != (float) PEAK_VAL) {
fprintf (stderr, "Oh well, thats just your FPU.\n");
}
>I still think that the only reason we have a 24 bit integer is to overcome
>the limitations in SNR of integer signals at low amplitude.
Interesting perspective. I've never seen this voiced in any of the
trade rags - they all seem to want the larger dynamic range that 24
bits offers, because of the difficulty of keeping a widely varying
signal from clipping at the same time as keeping it "hot".
>Why is bits-in == bits-out so important?
>We are talking about losing bits that are over 120 dB down. No one is ever
114 actually, and
sometimes less. eh, no
difference.
>going to hear it. You have to be in a very quiet place to hear even -60 dB.
>The only reason those bits need to be there for integer signals is to
>represent the quiet signals. FP doesn't have a loss of quality problem for
>quiet signals.
Who can hear sample accurate response to MIDI controller data ?
Just as SC puts a premium on real-time, sample accurate performance, I
think that software that does HDR should be able to do what dedicated
digital recorders do. If you were about to buy or download a software
HDR system, and then heard that unlike an ADAT or DAT recorder, it
dropped bits (albeit from the low end), what do you think you would
do? More importantly, what do you think most professional studio
owners will do?
All that said, I suspect that the benefits of converting to 32-bit FP
probably outweighs the disadvantages, for precisely the reason you
provide. Being able to run a bunch of really hot channels into the
same bus, and never worry about clipping is a nice feature, even if
the int32<->float32 performance of the x86 sucks bigtime. Its just a
question of how to deal with the question about bits-in vs. bits-out
in a way that won't scare away people used to "perfect" recording from
digital devices.
--p
This archive was generated by hypermail 2b28 : Wed Mar 22 2000 - 09:03:48 EET