[time-nuts] Using cheap sound cards for measurements

[Lux, Jim (337C)]

The idea of using a standard stereo sound card interface to do Allan deviation measurements has been discussed on the list in the past (i.e. Beat the two signals down to some convenient audio frequency, digitize, and find zero crossings by curve fits to the sampled data).

Several have commented that one needs good isolation between the channels of the digitizer to get good results, and inexpensive interfaces (e.g. The one that comes on the motherboard) often don't have good isolation.

Here's a question.. Is that coupling determinstic and "calibrate-out-able"?  Seems that the factors leading to lack of isolation are things like layout, capacitive coupling, shared ground paths, and the like.  If the card is in a constant environment, those shouldn't be changing, so, in theory, one could somehow measure it, and apply the inverse transformation.

Jim