Magnus Danielson wrote:
Bob Camp wrote:
Hi
My main concern with the low frequency pole in the sound card is the
quality of the R/C used. You can certainly model what ever you have.
If they used an aluminum electrolytic for the "C" it may not be the
same next time you check it ....
Do consider to bypass it. This is routinely done both by audio folks
and various other. The cap is there to remove DC offsets which can be
problematic in audio editing. I am quite sure you feel at home with
the soldering iron to do that upgrade.
On a 10 Hz system, a 1 Hz pole is probably not an issue. It might get
in the way with a 1 Hz beat note.
Another thing I have only seen in passing: "Sigma Delta's have poor
low frequency noise characteristics". I haven't dug into it to see if
that's really true or not. If you buy your own ADC's, you certainly
would not be restricted to a Sigma Delta.
Strange, most Sigma Delta's I have seen would have the opposite said
about them. It's the upper end that is problematic.
Even with a cheap pre-built FPGA board, you could look into higher
sample rates than a conventional sound card. You would drop back to
16 bits, but it might be worth it.
In fact, one of my FPGA demo-board does 3 MS at 14 bit. Crappy for
audio, but maybe good enough for this application.
Cheers,
Magnus
_
A pity that there is a relatively low bandwidth PGA used to drive the
inputs of that dual channel simultaneous sampling ADC.
Bruce
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