Ayre CX7e vs. Meridain G08

Bigtee -

I have noticed the same phenomenon you have -- increasing levels of jitter over the years in the Stereophile test reports. JA made an oblique reference to this in one or two of the testing sidebars -- something to the effect that you can't compare the numbers in the newer test reports with those of the older test reports. Unfortunately, he did not say why.

I tried to duplicate his test results for the Ayre C-5xe with a slightly different setup. The test disc is easily made, using specifications from an AES paper (by the late Michael Gerzon, I believe). I analyzed the output with the FFT function of both an Audio Precision System One (and older machine like Stereophile uses for most of their measurements), as well as the latest, greatest Audio Precision 2722.

With the System One, there were a lot of spurious sidebars as well as a generally higher noise floor than JA reported with his Miller Audio Research analyzer. But with the 2722, the noise floor was markedly lower than JA's tests. Further there were *no* sidebars at all when using 24-bit data, implying that all of the sidebars I found with that machine in 16-bit mode were data related and therefore an artifact of the test itself.

My conclusion is that this test protocol is extremely sensitive to the test equipment being used. I further speculate that something has degraded in JA's test setup over the years, leading to falsely high readings in more recent tests.

This is unfortunate, as many readers rely on these test reports. I hope that JA addresses this issue soon, and preferably in print.

Charles Hansen
Ayre Acoustics, Inc.

Hello Zaikesman,

Sorry you choose not to believe me. Here is proof of what I am talking about:

Go to the bottom of Stereophile's review of the dCS Verona master clock:

http://stereophile.com/digitalprocessors/305dcs/index4.html

and you will see the following footnote:

"Footnote 1: For reasons unknown, all these measured jitter levels are about twice what I measured for the Elgar and Verdi two years ago. They should therefore be considered as relative rather than absolute values."

Now I don't know about you, but I consider a 100% variation in test results over a two-year span to be problematic at best. I did contact him about this several months ago, but with no substantive reply to date. I suspect that he is pretty busy and that this is not high on his priority list.

Charles Hansen
Ayre Acoustics, Inc.

Based on my own brief measurements using the Audio Precision 2722 analyzer (this is a $27,000 piece of test equipment with an FFT noise floor at almost -140 dB), I think that this particular test protocol is flawed. I suspect that for well-designed digital audio equipment, the test tends to measure the noise floor of the analyzer/computer rather than the device under test.

I think Bigtee is right that the higher jitter levels in JA's test reports started showing up around two years ago. Maybe the increased jitter measurements in JA's test resulted from some change to his computer, perhaps the installation of a Wi-Fi card.