I think if we can make a simple switch box for analog sources that costs less than $50, we can always lend them one. Wonder how much work it is to have a simple tone generator and a digital meter for the output.
Thing is, tone generator does not even have to be clean in order to be used to measure level. 3.5 digit AC digital voltmeters are remarkably cheap nowdays. The tone generator does not even have to be super-stable level, as long as there's no drift inside of 5 minutes. You just have to get the levels right and leave it at that.
Question is how does one randomize A/B, or alternately (and better) X? That requires some thinking, maybe.
Having a button you push to "set up test" that simply has a high frequency oscillator (of indeterminate frequency, really) pick X from one of A or B via flipflop (having A and B fixed and known is the best setup for a test) isn't truly random, but it's quite close. If you're going to use a box like this, you'll want to have break before make, unfortunately. It would be nice to be able to use analog switches, but they frankly aren't that good, so a dry relay contact is the better choice. This means you have "clicks" from signal interruption, which does lower the test sensitivity somewhat, but it's not catastrophic except for very, very sensitive tests. It's certainly better than most options. This doesn't address looping, but that's a different hard problem.
If you're doing this, then you only need moderate time alighment, a dozen samples here or there isn't a problem. 10 milliseconds would be, though, there are drummers who would notice in two beats, at least.
If you do it that way, make the time delay (for the no signal part) fixed if you can.
Last edited: