18 Jul
2011
18 Jul
'11
11:53 a.m.
On Mon, Jul 18, 2011 at 9:38 AM, Erik de Castro Lopo wrote:
Moshe Werner wrote:
AFAIK everything Jack (including Ardour) uses single precision 32 bit
floating point samples. (Not 64 bit double precision as Erik suggests
- or am I wrong here?)
32 bit floating point gives a dynamic range of ~192dB, well above the
dynamic range of our hearing or any analog audio hardware, leaving
ample headroom for rounding errors to disappear.
I would not speak of inferiority or superiority when comparing this
and 48 bit integer calculations of pro tools. Single precision floats
as jack uses them will not be the bottleneck of SN ratio or any other
performance measure, the same is most likely true for anything pro
tools does. (I'm sure it is, just writing "most likely" 'cause I
don't
*know*)
Giving this[1] paper a quick look, they use the term "double
precision" for 48 bit integer, probably relating it to the 24bits of
the DA/AD converters. All that
bit-shifting/truncation/extra-headroom-bits-stuff mentioned there is
related to the integer format and does not apply to floats.
[1] http://akmedia.digidesign.com/support/docs/48_Bit_Mixer_26688.pdf
best,
d
Dale Powell to me
That 48 bit thing could hark back to Protools when it used the Motorola
56k DSP chips:
https://secure.wikimedia.org/wikipedia/en/wiki/Motorola_56000
which are fixed point DPS chips.
According to this:
https://secure.wikimedia.org/wikipedia/en/wiki/Protools
Protools uses 48 bit fixed point arithmetic (possibly doubled 24 bit
registers of the Moto 56k or possibly custom hardware).
64bits is double (comes from 32bit computer
architecture, so double uses
two words per value.)
Single generally uses 24bit values and 8bits of exponent.
Double uses 53bit values with 11bits of exponent.
Oh I see. So whats this Pro tools 48bit mixer talk about that goes on in the
industry? Why would it be better or more precise than the
Ardour mixer (which i prefer
over Protools).
If it is 48 bit fixed point I would think that it is inferior to
Ardour which almost certain uses double floating point which has
a 53 bit significand.