momerath wrote:
Phil is absolutely correct that the burden of proof is on the
audiophile, and that a double blind study is the only practical way to
prove the audibility of jitter. I intend to do this in the near
future with some skeptical friends.
By all means, if you can run a controlled test, then do it!
I'm not sure how to best go about that. I know of some audio ABX testing software, but I think it's designed mainly to evaluate lossy codecs. You're testing something at a much lower layer. It might be possible to simulate the effect of jitter in software by using similar algorithms to those that convert between sampling rates, although here the rates would be very nearly identical. This might not satisfy everyone, though, as it wouldn't actually test the real hardware, so an actual hardware switch would probably be the best as well as the simplest.
The most crucial thing in any audio A/B test is level matching. Otherwise, the louder signal will almost always sound "better". This shouldn't be hard to do in an all-digital system; just make sure identical bit streams come out both cables. Also, make sure that all switching transients and propagation delays are the same; if you do a test that involves A vs A and A vs B, you don't want the lack of a switching transient or change in delay in the first case to give it away.
Keep in mind that a positive result will be less conclusive than a negative result, at least with that particular subject. A positive result could be due to some artifact other than the property you're trying to test (e.g., different audio levels, different time delays, etc) and you've got to carefully exclude every possible artifact other than the one property (jitter) you're trying to test.
There's a classic example given in a MIT science textbook about just how incredibly hard it can be to design a proper experiment on human perception. It asked the question "Can humans detect magnetic fields?" The answers kept coming up "Yes", but closer examinations kept finding various bugs in the experiment that explained the positive results (e.g., the test subjects could hear the buzzing of the electromagnets, or saw the slight dimming of the lights as the switch was thrown, etc.) Eventually, after going to very great lengths to eliminate all artifacts, they got their answer: No, humans cannot detect magnetic fields, at least not at the intensities tested.
Let me know what happens!
--Phil _______________________________________________ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
