Re: USB Sound Cards? Good to adapt for stuff?

Joerg <notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote in
news:r0jkg.44845$fb2.27141@xxxxxxxxxxxxxxxxxxxxxxxxxx:

Lostgallifreyan wrote:


Nope :) Definitely input, one of those sockets is a stereo mic input.
This thing might not be suitable, as people have said, but that would
be because it's stuffed full of DSP I don't want and maybe can't
bypass (although if it IS the Micronas chip, it is apparently user
controllable by some means I don't know yet). I just want a cheap way
to get 16 bit voltage conversion in and out, and the USB idea is
appealing. If I can get this in something cheap and mass-produced, I
will, there's no point in re-inventing the wheel at inordinate
expense..


There may be a quick and dirty option: Find out the highest frequency
it can process reliably and with enough dynamic range. Then chop the
slow input signal at that rate. A simple CMOS oscillator and a gate or
FET can do that. You may lose some bits but hey, if it's good enough
it might work.


Nice. :) I think that might just do it.

One other thing I'm thinking is that the HPF on an IC might be disabled, if
the IC designer was generous about this.

The Echo Layla 20 bit audio rack unit is a VERY tempting device for laser
scanner control and other things, monitoring laser power, general lab
monitor and control. Echo Audio kindly sent me the I/O data*** in PDF.
I've found that the ADC is a Cirrus Logic CS5335-KSEP and with a bit of
fine surgery pin 1 can be made to control DC offset, and a DC blocking cap
can be bypassed. Currently, if I try to bypass the DC block cap, the result
is white noise in that channel, I have NO idea why, it really is odd, that
one..

If I can solve this, the CS5335 pin 1 will be a nice control, when low, it
tracks an onboard op-amp's DC output and cancels it, when high, it makes
the offset compensation freeze, so I can short an input, hold low for a
second, then raise high to eliminate any offset between the short and the
DAC input inside the CS5335, regardless of source, an extremely useful
feature. I hope the Micronas or similar IC in those cheap USB thingers can
be modified for this, but I suspect they might not provide a means to
bypass the HPF, even though they do apparently offer some control.

All this sounds tedious, but it beats having to build from scratch every
time, especially when 8 ins, 10 outs, at 20 bits or better (plus 2-channel
S/PDIF I/O at 24 bit), can frequently be found on eBay for £70 or so.
Beside the prospect of adapting that, all ideas of self-build look as
appetising as a pair of used boots on a plate.

Your fast-chopping idea is nice though, if it works, it won't matter what
the input processes are, at 20 bits I might still get to keep an accurate
16 bit log. These digital multi-channel things put out sync signals too, so
I guess if I can derive something from that I can reduce bit-loss by making
the chopper sample-accurate.


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