kimr@azure.UUCP (Kim Rochat) (08/20/85)
> Hearing differences and not being able to agree on what they are > is a typical result of very slight level differences. Since you didn't > match levels, how do you know that mismatches don't account for > the differences you think you heard? I've been hearing a lot from alice!ark about level matching to with .01db (at what frequency?) for CD player comparisons. What I haven't been hearing anything about is how he controls for absolute phase differences between players. We all know from looking at Len Feldman's tests in Audio magazine that CD players in general tend to be haphazard about observing correct polarity for the output signal. There is an excellent discussion of absolute phase in "On the Audibility of Midrange Phase Distortion in Audio Systems" (Lipshitz, Pocock, and Vanderkooy, JAES Vol 30, #9, Sept. 1982), which includes the observation that "(absolute phase) is an audible factor, and should be taken into account when performing comparisons of audio components." Just as ark discounts all CD comparisons which do not control for amplitude, I discount his comparisons until he shows that he controlled for absolute phase. (Of course, another popular position is that the differences between CD players are so gross that you can hear them without controlling for either) I submit that the differences reported heard between CD players in this forum (soundstage, image placement, hardness) more closely correspond with the effects of different absolute phasing than the effects of different amplitudes. Kim Rochat tektronix!azure!kimr
jj@alice.UUCP (08/21/85)
Kim Rochat demonstrates a typical sort of attitude for nut.audio, i.e. Rochat says: ".. discount all of your tests until you control absolute phase" (that's paraphrased, it's not worth dragging out of the file) This person then goes on to point out that absolute phase is a necessary condition for comparisons, and provides several references. All fine and dandy (and true), except for one thing: ABSOLUTE PHASE IS INDEED IMPORTANT, AND CAN MAKE TWO EXACTLY IDENTICAL SIGNALS (EXCEPT FOR INVERSIONS) SOUND NOTICIBLY DIFFERENT. WE DID NOT HEAR ANY SUCH DIFFERENCE, thus, by the publicly available information, the absolute phase must have been right :-(hey, fancy that, us people in NJ can actually do something right. Amazing, isn't it? :-( Furthermore, since Rochat knows that, Rochat can extract the answer to Rochat's own question. None the less, Rochat takes the popular view and attacks. Fascinating, isn't it? -- SUPPORT SECULAR TEDDY-BEAR-ISM. "I see a dark cloud, On the horizon,..." (ihnp4/allegra)!alice!jj