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CD TEST DISCS Reviewed by Gary A. Galo Digital Test: 106 Digital Tests and Demonstration Tracks, Pierre Verany Compact Disc PV.788031/32 (2 discs); Disques Pierre Verany, Celony, B.P. 206, 13607 Aix-En-Provence, France; $34. Available through Old Colony Sound Lab. PIERRE VERANY'S DIGITAL TEST is the finest collection of compact disc tests yet assembled. The two discs, the first is nearly 74 minutes and the second is 50 minutes, cost $11 less than CBS charges for CD-1, their single CD test disc (see my CBS review in TAA 3/88). I never considered the CBS disc a bargain, and in light of this new arrival, it appears greatly overpriced. While the CBS tests conform to the EIA standards (plus three of their own), the Verany discs are much more comprehensive. Perhaps the least useful tracks on Digital Test are the first twelve musical demos. I was not particularly impressed with these recordings. All sound bright in tonal perspective and are extremely cold and analytical. I'm sure many TAA readers own many CDs that sound far more natural than these. Two full orchestral selections are included. The third movement from Jolivet's Second Trumpet Concerto is played by Bernhard Soustrot with the Orchestre Philharmonique des Pays de Loire conducted by Marc Soustrot (probably a relative). The same orchestra and conductor are featured in an excerpt from the last movement of Rimsky-Korsakov's Scheherazade. Both recordings feature wide separation and plenty of ambience, but are two-dimensional; the instrumental locations lack a sense of depth. The lackluster performances and Soustrot's raucous trumpet playing are completely out of character with Jolivet ’s music. The first selection, although billed as a musical test, is a live recording of fire works, complete with audience noises, and reminds me of those old Russian roulette records from the early days of stereo. Perhaps the best musical demo is Jeux Interdits, played by guitarist Arnaud Dumond. This recording is extremely natural, although the guitar seems a bit wider than normal. The 94 (count 'em) bands of CD tests will be of greatest value to TAA readers, beginning with a 1kHz, 0dB reference tone, recorded without pre-emphasis. This is most useful for making a quick check of a modified player to ensure everything is working properly. Next, the left/right separation tests use a 1kHz tone only, compared to the CBS disc tests at 125Hz, 1kHz, 4kHz, 10kHz and 16kHz. I'm not convinced that separation tests at frequencies other than 1kHz are really necessary anyway. Unlike analog playback systems, where mechanical characteristics of the cartridge can cause the separation to vary substantially with frequency, the CD does not suffer from such problems; although Dave Hadaway reminds me that while this is strictly true of CDs, in some players separation can be reduced by 40dB at 20kHz, due to crosstalk in the wiring of the analog sections. Since the digital end of the player maintains separation of over 90dB, the reduction still leaves you with over 50dB of separation, which is better than any phono cartridge and as good as most amplification devices. In my experience, CD player imaging has little to do with the static channel separation figure and much more to do with the dynamic characteristics of power supplies. I certainly wouldn't buy the CBS disc just to get the separation tests at the other frequencies. Two swept frequency response tests are included at levels of 0dB and - 20dB. For the harmonic distortion tests, CBS chose the tones relatively prime to the sampling frequency of 44.1kHz, so they are set at 61, 127, 251 and so on; up to a maximum of 19,997Hz. The Verany disc departs from this approach and sets the tones at the usual round numbers, starting at 20, 50, 100 and 200Hz, and working their way up to 15, 18 and 20kHz. The signal-to-noise tests are at the digital zero level (infinite zero). CBS pro vides only one test, without pre-emphasis, but the Verany disc provides one with and one without pre-emphasis. Four de-emphasis tests are included on the Verany disc; CBS provides no such tests. For transient signal tests, Verany includes square waves at 400Hz and 1kHz, plus tone burst tests at 400Hz and 4kHz, which are a valuable inclusion. CBS provides only a 1kHz (actually 1,002Hz) tone. The merits of 16-bit versus 14-bit quantization are controversial, and the Verany disc includes a musical test to allow you to judge for yourself. The opening of the last movement from Dvorak's New World Symphony is presented with 16-, 15-, 14- and 8-bit resolution. I'm sure that no one will argue in favor of an 8-bit system. As the liner notes point out, the background noise is reminiscent of a 78 rpm recording. The Verany IM distortion tests include crosstalk between the left and right channels, with tones at 1kHz and 5kHz. Three mono IM tests are provided, with pairs of tones at 50Hz and 7kHz, 400Hz and 7kHz, and 19kHz and 20kHz. These, unlike those from CBS, do not follow the antiquated SMPTE standard of mixing the low and high frequencies in a 4:1 ratio; both tones are at the same level. Disc 1 concludes with overload tests featuring test tones and music. Three levels of 1kHz tones are provided, at 0dB, +3dB and + 6dB respectively. You won't need a distortion analyzer to confirm that something is amiss on the overloaded tracks. Finally, two tracks from Smetana's Moldau are recorded at maximum levels of 0dB and + 9dB respectively. The overloaded track is quite un listenable and I don't believe you'll need a double blind test to confirm this. Verany justifies the musical test, stating, 'Furthermore, is not music the only and final aim of all audio technologies?' A laudable goal, I agree. Disc 2 is designed to verify the mechanical, digital and processing performance of the player, and you can also test the compensating and servo systems. Test Series #1 varies the linear cutting velocity from 1.2 to 1.4m/sec, which are the outside tolerances of the CD standard. Many CDs are not cut at precisely the same speed, so your player must be able to handle discs within this range. Remember, unlike the LP setup, the CD's rotating speed varies across its playing surface. The disc starts at 500 rpm at its inner track and gradually slows to 200 rpm at the outside (CDs play from inside to outside). The result is constant surface speed across the entire disc. Test Series #2 contains variations in track pitch. A narrow track pitch is more difficult to read. The standard is 1.6um, but the tolerances allow pitch to vary from 1.5-1.7um. Two tracks are provided at each extreme, at a linear velocity of 1.4m/sec, followed by a test which varies the velocity while maintaining the maximum track pitch of 1.7um. Finally, 1.5 and 1.7pum track pitches are pro vided at a linear velocity of 1.2m/sec. Test Series #3 simply varies the track pitch from 1.7um down to 1.5um in five successive tracks. Test Series #4 tests the player's ability to detect the digital signal, simulating variations in cutting intensity, or asymmetry. The asymmetry is defined by the ratio of the pits to the flat zones. The greater the pits' depth, the easier the CD is to read. Very low asymmetry indicates a shallow pit depth. These tests vary the asymmetry from very low, to average, to very high; in five increments. I should mention my Magnavox CDB-650 (modified to beyond POOGE-4 standards) passes each of the Series #1-4 tests without difficulty. The remainder of the disc is devoted to dropout tests. If you look at the playing surface of the disc, you'll actually see these tracks of varying length, where no data is recorded. Test Series #5 contains 14 tests with dropouts ranging from 0.05mm to 4mm in 0.05mm increments. A 0.2mm dropout is considered the CD standard limit. My CDB-650 played the 2.5mm dropout without problems and only the last two tracks produced audible difficulties-exceptional CD player performance. Series #6 tests for dropouts at the minimum track pitch of 1.5um. These vary from 1mm to 2.4mm in four successive tracks. My CDB-650 can play any of these bands if you access the tracks individually. They sometimes produce an error display if they are accessed with the NEXT, PREVIOUS or REPLAY controls. Finally, Test Series #7 checks the player's ability to correct successive dropouts. These seven tracks each contain two successive dropouts ranging from 0.1mm to 3mm. The CDB-650 made it to 1.5mm without problems, but above that it produced the error display. I've had many people try their ‘defective ’ CDs on my Magnavox players and these usually play without incident. This test disc verifies the excellent tracking capabilities of the Philips-made players. An accompanying, well-written book let explains all the tests in detail, al though the English translation is occasionally awkward. Pierre Verany's Digital Test is an indispensable addition to your test bench (or listening room), and it puts the CBS test disc to shame. This two-disc set is the one to own, and the price is a bargain. ------------------- Also see: STRETCHING MARSH'S PREAMP, By Thomas Howe |
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