On Mon, 18 Jul 2011 11:53:47 +0200 David Adler <david.jo.adler@xxxxxxxxx> wrote: > On Mon, Jul 18, 2011 at 9:38 AM, Erik de Castro Lopo wrote: > > Moshe Werner wrote: > > > >> Dale Powell to me > >> > >> > 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? > > > > 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). > > > >> 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. > > > 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 > isn't it useless going way above 24 bits, since that's what in the end the DAC (sound card) will use? as far as I can remember, delta-sigma DACs don't go over 24 bit, do they? cheers renato _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
