Vir Campestris wrote:
Phil Allison wrote:



Your device will work perfectly when you are comparing two amps.


** Yes, and the result shows how useless all A then B tests are and by implication variations like ABX.

Soon as you pause and repeat a passage of music, imaginary differences appear.

People who auditioned my test set up were first given and A then B test using a music track known to them, in a quiet, well damped room and listening via Quad ESL57 speakers. The track could be from an LP or a CD.

All heard clear differences in this test - even me.

Then they were handed the switchover button and could swap amplifiers any time they liked while listening to the same track.

All reacted the exact same way, with a puzzled look and told me the button was not working. So I turned off the AC power to one amp and showed them it was.

The smarter ones got it, realising that the previously heard differences were the result of imperfect memory. The less smart ones were dumbfounded.

I loaned the set-up and spare amp to one audiophile in the above category to use at home for a week - at the end of which he agreed the amps sounded the same, a reversal of all his previous opinions.


I daresay a variant of it would work well with two speakers.

** Speakers DO sound different, as one would expect, since they do not test the same. Having an instant changeover makes comparison tests very easy though and eliminates imaginary differences.



The difference with digital encoding is that there may be a difference
that is not perceptible. If the phase of the bass is inverted nobody
will notice - probably not even if its harmonics aren't. But your box
would cause a click when switching such a pair of signals.


** Yes, a phase reversal would cause an audible click when doing the set up procedure - especially if a sine tone were used.


When I merge two digital signals I try to do it on a zero crossing
point. Your box won't.


** When crossing from one signal to an identical one, using a changeover relay, the interruption is under 1mS and as I found non-audible on programme.

The relay itself could just be heard, when the room was dead silent.


.... Phil