[time-nuts] A/D specs (was EFC tracking)

Hal Murray hmurray at megapathdsl.net
Sun Jun 27 06:38:37 UTC 2010

jimlux at earthlink.net said:
> So, over the, say, 100 Hz and up range, they're probably pretty good. 

I like to think I'm pretty good at reading data sheets, but when it comes to 
modern A/D chips, I'm not so sure.

20 years ago, the specs were for DC and you hoped it did something sensible 
at high frequencies.  Now the specs for many chips are for AC (typically they 
show a FFT plot) and you are in trouble if you want to use it for DC.

Typical audio A/Ds are oversampling with a low pass filter implemented in 
DSP.  This makes the anti-aliasing filter a lot simpler/cheaper.

Has anybody tested modern audio A/Ds at very low frequencies?

Is there some simple way I should be thinking about this tangle?

Has anybody tried adding a signal, say 1 KHz, and filtering it out?  I'm 
fishing for something along the lines of the old chopper amplifiers - shift 
things to a mode that is known to work well and then filter out the junk you 
don't like.

These are my opinions, not necessarily my employer's.  I hate spam.

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