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dCS 972 D/D converter Measurements

Sidebar 4: Measurements

It must be clearly understood that upsampling from 44.1kHz to 96kHz or 192kHz doesn't add high-frequency information that was above the Nyquist Frequency—22.05kHz—of the first, lower sample rate.

This is graphically shown in fig.1, which shows the the dCS 972/Elgar's frequency response of the digital signal for three different input conditions. In all three cases, the 972 was set to output a 192kHz datastream to the dCS Elgar, and the Audio Precision System One output an analog sinewave (swept from 20Hz to 100kHz) to a dCS 904 24-bit A/D converter. The…

dCS 972 D/D converter Measurements part 2

To examine what the dCS 972 does when it increases word length, I generated a 16-bit datastream with the PrismSound DScope. Again, this datastream represented a 1kHz tone at -0.1dBFS, and I set the 972 to output this data with a 24-bit word length, as well as adding dither with a triangular probability density function (PDF). These data were fed to the DScope analyzer's digital input. The resultant spectrum is shown in fig.5. The spectrum looks a little smoother, but otherwise appears identical to the 16-bit spectrum shown in fig.4. The greater word length does not result in increased…

dCS 972 D/D converter Measurements part 3

I repeated these tests using the Audio Precision System One's AES/EBU output to drive the Elgar, then redigitizing the analog signal at a 24-bit word length with the dCS 904 ADC to drive the 972 at both 96kHz and 44.1kHz rates. The results with a 1kHz tone were comparable, though things did look better with a more complex signal.

Fig.8, for example, shows the DScope-derived spectrum of a signal consisting of 19kHz and 20kHz tones at equal levels, sampled at 44.1kHz and passed through the 972. The 1kHz, 2kHz, 18kHz, and 19kHz intermodulation products are all at very low levels, and the…

dCS 972 D/D converter Measurements part 4

The grayed-out spectrum shows the performance of the Meridian 508.24, which, at 144.2ps, is similar to the Elgar's. But note the rise in noise either side of the Meridian's central peak, as well as the relatively high-level, low-frequency sidebands. The Meridian, however, has slightly lower levels of data-related jitter, which is to be expected given the fact that the Elgar has to receive its input via an inherently jittery AES/EBU link.

Inserting the 972 in the chain but keeping the sample rate to 44.1kHz dropped the Elgar's jitter even lower, to just 132ps peak-peak, which is superb…

dCS 972 D/D converter dCS 972 Followup, January 2001

Sidebar 4: dCS 972 Followup, January 2001, Vol.24 No.1

I first auditioned and reviewed the dCS 972 digital-to-digital converter back in February 1999 (Stereophile, Vol.22 No.2). Until the Accuphase upsampling/oversampling gear showed up, the dCS 972/Elgar combination was pretty much as good as it got around here.

Well, a lot has changed since then, and the new 972 running v2.3.1 software is a much more capable "box." You'd be hard-pressed to fault it as a piece of pro gear. The 972 will do DSD and PCM from 192kHz to 11.025kHz. In the PCM world it supports AES/EBU, dual AES, S/…

dCS 972 D/D converter Another dCS 972 Followup, February 2001

A further followup appeared in the February 2001 Stereophile (Vol.24 No.2).

The dCS 972 and DSD

As mentioned in my January 2001 review of the dCS Purcell, the upgraded dCS 972 D/D converter (but not the Purcell) can suck in the S/PDIF output of a 16-bit/44.1kHz CD player and convert that signal to DSD, as well as upsample it to 24-bit/192kHz. After conversion, the 972 squirts the DSD datastream to the dCS Elgar Plus through a trio of BNC-terminated S-DIF 2 digital datalinks (left, right, clock). This arrangement is apparently a hot setup in Japan so this review seemed an ideal…

The Highs & Lows of Double-Blind Testing

Editor's Note: In 1985 and 1986, an argumentative thread ran through Stereophile's pages, discussing the benefits or lack of double-blind testing methods in audio component reviewing, triggered by J. Gordon Holt's review of the ABX Comparator. As this debate is still raging nearly 15 years later, we present here the entire discussion that bounced back and forth between the magazine's "Letters" section and features articles. It was kicked off by a letter from C.J. Huss that appeared in Vol.8 No.5.—John Atkinson

ABX...
Editor: First off, thanks for the enjoyable reading your magazine…

The Highs & Lows of Double-Blind Testing Page 2

The next volley, from audio writer, long-term Compuserve CEAUDIO moderator, and a leading light in the Boston Audio Society, E. Brad Meyer, appeared in "Letters," Vol.8 No.7:

A-B Testing
Editor: JGH's assertions in Vol.8 No.5 that he knows what the ABX box does and no longer needs it seem a bit disingenuous. The double-blind comparator exists because of the experiences of people who, like JGH and other subjective reviewers, noticed differences in components and wanted a faster and more reliable way to identify them. When, after level and frequency response had been very carefully…

The Highs & Lows of Double-Blind Testing Page 3

The statement "the number of correct identifications observed indicates that differences are audible at the .05 level of significance" roughly means the following: for a listener who cannot hear differences, there is no more than a .05 probability that he will by chance make as many or more correct identifications as the number actually observed. Were the same listening test repeated infinitely with this listener, no more than 5% of the replications would provide statistically significant data leading to the incorrect conclusion that the subject heard differences. In this instance, the…

The Highs & Lows of Double-Blind Testing Page 4

Thus, with a 16-trial listening test analyzed at the conventional .05 level of significance, the probability of the investigator overlooking differences so subtle that the listener can correctly identify them only 60% of the time is a whopping .8334! Accordingly, when true differences between components are subtle, it is not surprising that 16-trial listening tests with (or without) thc ABX comparator typically fail to find them.

What if 50 trials are run? The table shows that the investigator must require the listener to make 32 or more correct identifications (r = 32) to conclude that…