[PD] audio bit resolution in Pd

[Alexandre Torres Porres]

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.

thanks


2015-04-23 6:43 GMT-03:00 Julian Brooks <jbeezez at gmail.com>:

> Nice. Thanks Chuck, I learnt something.
>
> On 22 April 2015 at 23:45, Charles Z Henry <czhenry at gmail.com> wrote:
>
>> On Wed, Apr 22, 2015 at 5:11 PM, Alexandre Torres Porres
>> <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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