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So maybe I can help the communication


I did go back and look at the threads you referenced, and I saw lots of miscommunication in all directions.... Pity, given the potential value of real communication.

Somehow John and SE got into this bizarre thread concerning gain of a mac sound card, which as far as I know has nothing to do with the test...

So, here's what I saw at JC's:

Sound Tech 1700B (modified) acting as oscillator. Signal fed into cable under test. Output of cable goes into 1700B to null out the fundamental. Residual output of 1700B (minus the fundamental) sent to two spectrum analyzers. One is an old HP3580, the other is (from memory) an HP3563. The main difference is that the 3563 completes a measurement in much less time. The results were plainly visible on both scopes. The 3580 showed almost as much detail as the 3563. It just takes longer to do the measurements. The 3580 has a dynamic range of about 80dB, but of course we were starting way below the amplitude of the fundamental since we were looking at the distortion residuals.

I just bought a used 3580 on eBay for $300; don't know its condition yet... I'm not that concerned about its absolute calibration state, since my primary interest is in looking at the shape of the distortion spectra of equipment I build, rather than the exact magnitudes.

Peter


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