[PD] audio bit resolution in Pd
Alexandre Torres Porres
porres at gmail.com
Thu Apr 23 17:55:21 CEST 2015
I know there's a parallel discussion about human hearing and what audio
cards can get there. But I'm just trying to get one simple fact clear, that
is the bit depth of audio in Pd :)
Leaving the human hearing or audio cards aside, some DAW (like Pro Tools or
Ardour) do operate on audio files that are actual 32 bit resolution. I
guess the idea is to keep quantization error as low as possible when
mixing, normalizing, processing, filtering, mastering and everything. Then
you can convert it to, say, 24 bit high quality audio afterwards for
distribution - I guess this is the standard for highest digital audio these
days, meaning that it's pointless to have a final audio that's higher than
that, but then, 32 bit dac seem to be showing up already as chuck pointed
out, but I digress. Moreover, you can also convert it to 16 bit CD quality
afterwards, or even just make some MP3 or whatever...
Not to get into the discussion if dealing with 32 bits internally on a DAW
is really important or worth the hassle (and not even getting into the deal
with new 32 bit dac), the fact is that 32 bit audio exists out there for
some time now. They do have this 32 bits option, or even more maybe... (not
sure if they're pushing it to 64 yet, but it doesn't matter).
So, I always knew Pd was "32 bit", and knowing the above, I was misled to
think Pd was just like Pro Tools or Ardour, that it could process audio in
32 bit. But I was thinking about it these days and it hit me that you just
can't say Pd processes audio like Ardour and Pro Tools do on 32 bit
precision.
Bottom line, you can't!
So this made me wonder what the heck that precision would be...
Chuck made me think it was a bit more than 24 bits, now it seems Miller
says it's more likely to be 20 bits :)
cheers
2015-04-23 12:25 GMT-03:00 Miller Puckette <msp at ucsd.edu>:
> I get 1 000 000 = 2^19.9 so a 20 bit dynamic range.
>
> I don't think A/D/A hardware ever gets better than about 110 dB dtnamic
> range though.
>
> cheers
> Miller
>
> On Thu, Apr 23, 2015 at 05:20:51PM +0200, Cyrille Henry wrote:
> >
> >
> > Le 23/04/2015 16:41, Alexandre Torres Porres a écrit :
> > >Yep, nice indeed, I guess I learned - in short and in layman's
> undetailed terms - that audio output is ~24bits (a bit higher, but much
> higher for smaller numbers).
> > >
> > >Moreover, digital audio cards won't likely have more than 24 bit
> precision for many years to come, so it's just way more than enough.
> > The human ear is usually consider to be sensible from 0dB to 120dB, so a
> range of 10^(12/2) between the smallest and biggest amplitude.
> > i.e from 1 to 1 000 000, or from 1 to 2^13.8
> > so, the human ear sensitivity can be considered to be about 14 bits.
> > 16 bits diffusion should be enough.
> > 24 bits diffusion is already overkill.
> >
> > cheers
> > c
> >
> > >
> > >thanks
> > >
> > >
> > >2015-04-23 6:43 GMT-03:00 Julian Brooks <jbeezez at gmail.com <mailto:
> jbeezez at gmail.com>>:
> > >
> > > Nice. Thanks Chuck, I learnt something.
> > >
> > > On 22 April 2015 at 23:45, Charles Z Henry <czhenry at gmail.com
> <mailto:czhenry at gmail.com>> wrote:
> > >
> > > On Wed, Apr 22, 2015 at 5:11 PM, Alexandre Torres Porres
> > > <porres at gmail.com <mailto:porres at gmail.com>> wrote:
> > >
> > > > So I start with this idea that the audio (values from -1 to
> 1) can't be in
> > > > full 32 bit float resolution, it's less. I don't see why that
> is "wrong".
> > > > And then, from it, my first question here was: "what is the
> audio resolution
> > > > then?". I'm still clueless here about this answer.
> > > >
> > > > Moreover, is it more or less than what 24 bit audio cards
> handle?
> > >
> > > Let me try:
> > >
> > > 32-bit floating point numbers have 24 bits of precision.
> Always. The
> > > remaining 8 bits are just for the sign and exponent. When the
> > > amplitude of the signals decrease, you don't lose any precision
> in
> > > floating-point. The value of the least significant bit (LSB)
> gets
> > > proportionally smaller.
> > >
> > > However, the output of a 24-bit soundcard always has a fixed
> > > quantization. The LSB is always the same size. Smaller
> numbers have
> > > less precision.
> > >
> > > The mismatch occurs when converting from the 32-bit floats to
> the
> > > 24-bit fixed point numbers. Now, the smaller numbers aren't as
> > > precise anymore. They get rounded to the nearest number in the
> 24-bit
> > > fixed point system.
> > >
> > > So, yes, the resolution (of small numbers) in floating point
> (internal
> > > to Pd) is finer than the resolution of those numbers when output
> > > (driver/DAC).
> > >
> > > Also, the 24-bit fixed point format is for values between -1
> and 1.
> > > That means that numbers between 0 and 1 have just 23 bits. In
> 32-bit
> > > math, the numbers between 0.5 and 1 still have 24 bits of
> precision
> > > (the sign is held elsewhere). That means that Pd's internal
> > > resolution is finer than the soundcard resolution for all
> numbers
> > > between -1 and 1.
> > >
> > > Chuck
> > >
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