Subject: Re: [linux-audio-dev] LADSPA 64bit FP support ?
From: James McCartney (asynth_AT_io.com)
Date: Wed Mar 22 2000 - 05:29:43 EET
I'd like to see a real world example where you have a signal that is full 24
bits peak to peak and you can hear some distortion in the low 4 bits.
Because other than full scale peak to peak signals you will not lose the
lower bits using 32 bit FP. The additional bits in integer formats is
usually for the increased dynamic range, not increased SNR. 16 bits is
already sufficient if it were just SNR.
In any case SC unit generators have a typedef for the sample type which can
be changed easily and recompile. But I don't see a real world need for more
than 32 bit FP. No one is going to hear the low bits in a full scale signal.
> 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.
You are mixing up terms here. 32 bit FP has 151 bits of dynamic range
(=log2(FLT_MAX/FLT_EPSILON)), but only 24 bits of signal to noise. You don't
need as much SNR as you do dynamic range. Most manufacturers of digital
equipment mix up these terms as well in their published specs. A 24 bit int
signal has 24 bits of SNR, but the dynamic range depends on the amplitude of
the signal. With FP the dyanamic range doesn't depend on the amplitude for
any practical purpose.
> As an example that most of you have probably experienced [...]
This example is all about the limitations of integer formats, not FP. Not
much that a plug in API can do about converter limitations.
--- james mccartney james_AT_audiosynth.com <http://www.audiosynth.com>
SuperCollider - a real time synthesis programming language for the PowerMac.
<ftp://www.audiosynth.com/pub/updates/SC2.2.7.sea.hqx>
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