Re: [linux-audio-dev] float a/d (was Linux support for IEEE1394 mLAN?)

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Subject: Re: [linux-audio-dev] float a/d (was Linux support for IEEE1394 mLAN?)
From: Paul Barton-Davis (pbd_AT_Op.Net)
Date: Thu Sep 28 2000 - 04:00:32 EEST


>1) In a digital mixing environment, where everything is a plug-in, is
>it preferred to convert the audio to float before performing dsp always,
>most of the time, occasionally, or never? Benno suggests converting to
>64 bit double precision float as policy.

in every system i know of, it would be converted to a float as the
first step (i.e. after the program has read data from the audio
interface), or never. in VST systems, for example, it would be
converted to floats by the VST host, then every plugin would get float
data.

i don't believe that 64 bit floats are necessary, but i also don't
believe that they are a problem either. i think that karl did a pretty
good job of explaining why this stuff about "resolution loss" is
relatively bogus.

>2) When converting audio samples to float, either from the soundcard or
>from hd, is the overhead associated with this conversion high enough
>that storing audio to disk as float or delivering audio from the
>soundcard as float would provide a meaningful performance gain, since
>conversion immediately prior to dsp would no longer be necessary? Also
>consider the overhead of converting back to integer for final output,
>since this can also be eliminated by using float dac's.

benno measured this at some point, and i think the answer is basically
(1) its CPU dependent (e.g. Alpha's and MIPS can do this much faster
than Intel x86) and (2) the conversion-upon-loading-from-disk or
reading-from-audio-interface pretty ignorable even on the worst CPUs.

>3) Are the currently superior low pass, band pass, and high pass
>filters using float or integer math?

no clue.

--p (and once again, i've spent another hour answering email
     instead of writing code. sigh.)


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