--- In Philip Tyler
<> wrote:
>
> Some thoughts and questions.
> We often talk about 24 bit ADC but in reality it would
> probably be pretty difficult to actually achieve full
> 24 bit resolution.
> 24 bit would give us a range of 144dB, as someone once
It's important to consider the reference level and bandwidth. That
is -144dB on a 10V p-p signal is 223 nV rms. in a 20kHz bw. This
resoluton could be physically achieved but at 1V p-p there is no
integrated amplifier for sure and not even the most exotic JFET
phono preamp I know of reached this noise level. The 600 Ohm
resistor is indeed -126dB but that is re 1V rms unweighted in the
same 20kHz bw. Also A/D's need to include linearity in there specs
so in the audio range there are few if any "real" 20 bit performers.
There are weigh scales (quasi-DC) that are 24 bits. I think the low
voltages and low power requirements hurt the performance of some of
these low cost recorders too.
BTW I got to play with a prototype "real" 24bit A/D from Panasonic
while helping a professor friend build "the world's best mic
preamp". We got the system down to a noise resistance of 22.5 Ohms @
60dB and -130dB THD @ 10V rms before we gave up. Panasonic gave up
too, they considered the A/D unmanufacturable.
Also thanks for this discussion, I've been hanging around trying to
help a friend who's working on an ambient sound art "installation".
He wants to capture acousticly the "feel" of water vorticies, etc.
|