[PD] audio bit resolution in Pd

Alexandre Torres Porres porres at gmail.com
Thu Apr 23 18:01:57 CEST 2015


> 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 :)

or I just got that way wrong and miller wasn't talking about this at all...
so I stick to chuck's answer.

cheers

2015-04-23 12:55 GMT-03:00 Alexandre Torres Porres <porres at gmail.com>:

> 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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