On Thu, Apr 06, 2006 at 07:51:15AM -0400, Timothy Miller wrote:
> On 4/6/06, Jack Carroll <[EMAIL PROTECTED]> wrote:
>
> > High speed Ethernet, or one of the other high-speed serial links,
> > breaks the dependencies between the expensive audio hardware and the
> > computer's interface standards. Besides getting the low-level analog
> > hardware out of the electrically noisy computer environment, it
> > future-proofs it. It cuts it loose from the constant standards churn in
> > PCs.
>
> One guy said "no on-board processing needed". But if we use ethernet,
> no matter what protocol you use, the latency added is potentially a
> problem. In that case, we would need on-board processing. Do you
> agree?
Yup, I agree. It takes non-zero time to convert the raw bit stream
into Ethernet frames. One feature the protocol would have to support is
synchronization of the streams coming from different digitizer channels,
including digitizers on different subnets. I'd say 10 microsecond
synchonization accuracy would probably be adequate; that's about 0.1" or 2.5
mm sound source location accuracy.
>
> > BTW, there's no such thing as a 32-bit DAC or A/D. With
> > thermodynamic noise in the range of a microvolt for a low-impedance mike,
> > that would require a full-scale signal level of +/-2148 volts. Aside from
> > that, physical components aren't stable enough for much over 20-bit
> > accuracy. What might make sense is floating poing with a 24-bit mantissa
> > and an 8-bit exponent; that would avoid the need to adjust levels during
> > mike check; it would facilitate automatic level control without sacrificing
> > dynamics.
>
>
> If the best you can do at max volume is 20-bit, what does it matter
> that you're down to 19-bits at 50% volume? Your lowest bit is still
> at your noise threshold no matter what.
Well, there are sigma-delta A/Ds with 24-bit resolution. They're
specialized for audio applications, and don't have absolute accuracy to
anything like 24 bits. They're not instrument A/Ds, in other words.
OK, with the preamp scaled for 1 uV/LSB, full-scale would be +/-8.39
V. That's probably enough to handle the full dynamic range of a mike input
without a mantissa or a level adjustment. You might want the resolution to
reach a little below the noise threshold, though. That leaves open the
possibility of digital filtering after the fact. Audio specialists probably
know more about this.
>
> What I think might be good is to have 24-bit samples but only a 20-bit
> DAC. If your recording level was too low, you could bump it up by
> four bits before losing dynamic levels. Of course, that requires a
> 24-bit ADC, which is a whole other problem. :)
> _______________________________________________
> Open-graphics mailing list
> [email protected]
> http://lists.duskglow.com/mailman/listinfo/open-graphics
> List service provided by Duskglow Consulting, LLC (www.duskglow.com)
_______________________________________________
Open-graphics mailing list
[email protected]
http://lists.duskglow.com/mailman/listinfo/open-graphics
List service provided by Duskglow Consulting, LLC (www.duskglow.com)
