[PD] audio bit resolution in Pd

IOhannes m zmölnig zmoelnig at iem.at
Wed Apr 22 23:25:53 CEST 2015

On 04/22/2015 10:10 PM, Alexandre Torres Porres wrote:
> [...] but this is the kind of information I'm after.

i know, but this doesn't mean that your answer makes (much) sense¹.

> It's clear to me that the resolution for audio streams sent from pd (with
> values between -1 and 1) can't be considered as "32 bits".

which is just wrong: Pd's audio samples are 32bit floating point.
as such they must be considered as "32bit floating point" which is a)
"32 bit" and b) something else as "16bit PCM" or "8bit ulaw" or what you
call "32 bits" (which is likely "32bit fixed point").

> My guess is that
> it'd be more like 24 bit precision or around that, considering most top
> notch audio cards only deal with 24 bit audio.

please don't.
when i started with Pd it used 32bit floating point values for audio
processing, and "most top notch audio cards" had 16 bit dac.
this is why Pd was then announced as doing "full CD quality audio",
which i always found very unfortunate, as Pd was doing way better than
just boring 16bit.

the bit resolution of your audio hardware (top notch, or low end, or
whatever) has *absolutely nothing* to do with the bit resolution of Pd.
your hearing experience might be directly related to the quality of your
soundcard, though.

> Does your answer state that audio in Pd is 24 bits?

no, it means that audio in Pd is "32bit floating point" (all right; i
think i made my point; i think i'm not very good at explaining the
difference between floating point and fixed point and what that means to
bit resolution; in any case you *should* read about floating point if
you are interested in those kind of things).

> Obviously, the actual resolution depends on the audio card. 

depends what you mean by "actual". but yes, what comes out of your
soundcard heavily depends on your soundcard.

> Which also
> makes me wonder how does the downscale/bit reduction work if, say, it's
> only a cheap 8 bit audio card, or 16 bits. I assume it's up to the audio
> card and audio driver, not Pd at all.

luckily Pd is blissfully unaware of audio cards used. it only queries
the audio backend about the name, number of available channels and
samplerate and then passes the samples to the audio backend which is
free to do whatever with the samples, but somehow takes care that they
end up correctly in the sound cards DAC)


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