[time-nuts] EFC tracking

jimlux jimlux at earthlink.net
Sun Jun 27 04:15:43 UTC 2010

Didier Juges wrote:
> I am not sure how to translate the IMD specs into integral or
> differential non-linearity, but from what I have seen, IMD specs are
> not significantly better for 24 bit sound cards than for the older
> high-end 16 bit models, when high-end 16 bit models were available.
> Noise specs are better, and that's about it.
> In sound cards as in many other consumer products, customers equate
> more bits to higher quality and today you cannot buy anything but 24
> bit cards, regardless of the actual improvement obtained. I am not
> sure the actual specs reflect the higher number of bits. I believe
> Bruce has quite a bit of data on that.

Some of the high end ADC parts (not necessarily cards, which could 
greatly compromise the performance) are quite good... they're sold into 
applications for professional recording as well as the consumer gear.

The (amateur) software defined radio folks have looked into this, in 
connection with direct conversion type receivers, because it affects the 
performance on things like instantantaneous dynamic range: being able to 
  demodulate a small signal next to a big one, for instance.

So, over the, say, 100 Hz and up range, they're probably pretty good.

> What I know is that the standalone A/D converters like the AD parts
> referenced in the other emails have outstanding linearity specs (at
> low bandwidth of course) at a price well below that of a "high
> quality" sound card, so even if the specs were the same, it would
> still make more sense to use the external device to measure a slow
> moving DC voltage.

I agree there..

> Didier

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