Re: LF: Testing Audioinjector Octo with RPi3

[Paul Nicholson <vlf0403@abelian.org>]

These glitches on the Octo input occur as the input signal
passes through about +/- 1.4 volts.   Regardless of the
digital gain control setting.

Still present if I bypass the input board and wire straight
into the differential inputs on the Octo card.

Vanishes if I sample at 48k/sec instead of 96k/sec.  I get
about 30nS jitter on the PPS at 48k/sec.

To eliminate vlfrx-tools I reproduced the fault using arecord
into sox to convert to ASCII data and then plot with gnuplot,

Occurs on two specimens of Octo and two Pi.

If I keep the input signal below 1.4 volts, there are no
noticeable artifacts but the PPS jitter is still no better
than about 200nS at 96k/sec.  The PPS is visibly noisy on
the scope at 96k/sec but looks clean at 48k/sec.

Tomorrow I'll look at the noise floor at various sample rates.

--
Paul Nicholson
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