[PD] audio bit resolution in Pd
Alexandre Torres Porres
porres at gmail.com
Wed Apr 22 22:10:22 CEST 2015
"*IEEE-754 (which defines the exact format of single/double precision*
*floating point values as used by most systems) uses 24bits for
thesignificand, which will correspond to 24bit fixed point around thevalues
+-1., but will already correspond to 25bit fixed point around the**values
+-0.5 and so on.*"
I'm not sure if I got this, but this is the kind of information I'm after.
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". 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.
Does your answer state that audio in Pd is 24 bits?
Obviously, the actual resolution depends on the audio card. 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.
2015-04-22 15:30 GMT-03:00 IOhannes m zmölnig <zmoelnig at iem.at>:
> On 04/22/2015 07:26 PM, Alexandre Torres Porres wrote:
> > Now, output audio values
> > is actually just from -1 to 1,
> where did you get that from?
> there is no -1/+1 in "audio".
> instead "audio" will have many different values (and units), including:
> - sound-pressure in the air (hmm, hard to make any actual numbers)
> - voltage at your sound-card output (+- 1V, depending on the line level
> in use)
> - digital values fed to your soundcard (depending on the the bit
> resolution of your soundcard, this might be +-32768 (16bit) or +-8388608
> - digital values output by Pd (many audio backends (e.g. jack) will use
> floating point as their intermediate format)
> now your question really only makes sense when you consider fixed-point
> values such as used by your typical soundcard (where you divide a range
> (e.g. +-1) into N equally small fractions (e.g. 1/32678 steps)
> but Pd uses floating point arithmetic, which does not have equal
> fractions but fractions depending on the current range of the value.
> so the quantization steps are rather largish when it comes to bigger
> numbers, but can be *very* small when it comes to small numbers.
> IEEE-754 (which defines the exact format of single/double precision
> floating point values as used by most systems) uses 24bits for the
> significand, which will correspond to 24bit fixed point around the
> values +-1., but will already correspond to 25bit fixed point around the
> values +-0.5 and so on.
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