Company Addresses:
ESX, do Essex Entertainment, 560 Sylvan Ave., Englewood Cliffs, N.J. 07632.
Sheffield Lab, 1253 Coast Village Rd., Santa Barbara, Cal. 93108.
Stereophile, P.O. Box 5960, Santa Fe, N.M. 87502.
Test signals on CD are produced digitally, with high precision, and are even more accurate than the laboratory oscillators which formerly generated the test signals for LP test records. Some engineers have found the test signals on CD to be so ac curate that they are able to replace portable test instruments. The four CDs in this report have test signals plus a variety of musical selections that can help you achieve better sound. Each was created with a specific idea in mind and employs different recording techniques for the musical se lections. Even so, there are certain similarities. For example, all of them have tracks for channel identification and proper phasing of the output; all of them are also very useful for checking out listening systems even if you don't have test instruments.
The first test Compact Disc that is reviewed here The Sheffield/Coustic Test and Demonstration Disc, which was produced by Sheffield Lab (10040-2-T) for Coustic and Kinergetics Research. It costs $19.95 and comes with a 12-page booklet. Track 1, "A Sonic Demonstration," has musical selections that are pre ceded by descriptions of what is to follow, and provides cues about what you should be able to hear if your system is performing well. Tracks 2 through 6 are complete selections from the Sheffield catalog. The voice on tracks 7 and 8 is for channel identification and phasing. A warning is given on track 9 that the next tracks contain test signals that should be used with caution. These tracks, 10 through 42, contain signals that were created by Richard Clark of Autosound 2000; tracks 28 through 42 are meant to be used with test equipment. I found that I could use the polarity test signal on track 10 to determine the absolute polarity of coherent earphones and loudspeaker systems by just listening. This signal has a four-pulse sequence, three positive pulses and a negative pulse, that repeats. When absolute polarity is correct, the three positive pulses sound "sharp and lean" and slightly higher in pitch than the fourth pulse, which sounds "slightly bassy and fat." I would describe the sound as "tick, tick, tick, tuck." The pink noise on track 18 can also be useful without instruments; just listen for coloration from your system. The sound should be smooth and wide band, without any definite pitch. Resonances in your loudspeakers or room--or reflections from room boundaries, furniture, etc.--can cause the sound to lack smoothness. If you move around the room and the character of the sound changes dramatically, you may have to reposition your speakers and perhaps do a little acoustical treatment of the room to achieve optimum results.
The Sheffield/XLO Test & Burn-in CD (Sheffield Lab 10041-2-T) was produced by Sheffield's Doug Sax for Roger Skoffs XLO Electric Co. Its price is $29.95, and it comes with a very useful 20-page booklet detailing the contents of each track and how the tracks containing test signals should be used. Track 1 is for channel identification and balance, and track 2 is for phasing. Track 3 is a "walkaround" test with Sax talking while moving around a very live room that measures 32 x 18 feet with a 13-foot ceiling; he also hits two claves together while he tells where he is in the room relative to the mikes. Near the end of the track, Skoff and Sax speak at the same time, which allows you to test the resolving power of your system; if you can distinguish what each is saying, your system (and your hearing) is very good! Track 4 has a consistent hand clap repeated over and over, so you can walk around your room and listen to the way your system reproduces the sound when you are in different locations. Track 5 has a 315-Hz signal that you can use with an inexpensive multimeter to set the same level from your amplifier to your loud speakers. Track 6 has a "demagnetizing sweep" signal that can be used to reduce any residual magnetism that may have built up in your system components. This is a relatively safe type of signal and pro vides a rather low level of demagnetization for resistor and capacitor leads, crossover inductors, cables, and phono cartridges. I haven't seen any scientific proof documenting the sonic effects of this type of low-level magnetization. Its proponents categorize it as being different from the residual magnetism that happens to a tape head due to asymmetrical low-frequency or d.c. signals. Internal copper wiring and p.c. board traces, they say, become magnetized, due to current flow, and degrade the conics. To say the least, it is controversial. I'll keep an open mind while I await scientific evidence and just say that using this signal is like "mother's chicken soup-it can't hurt"! Track 7 has a "low frequency demagnetizing fade," the more usual kind even the most highly magnetized devices; because of this it should be used with caution. It is intended to demagnetize low-frequency system components; I take this with a grain of salt also. Track 8 has "burn-in tones" that allow you to "exercise" any new components in your system. Tracks 9 through 13 are musical selections from the Sheffield catalog. The final track, 14, is an excerpt of track 9, only in mono. This track should appear to come from a small point between your loudspeakers; the better the loudspeakers, the smaller and sharper the point.
The Ultimate Test CD from ESX Entertainment (ESD-7059) has 45 tracks, comes with a 16-page booklet, and carries a price tag of $7.98. After the introduction on track 1, tracks 2 through 6 are for channel identification: Left, right, the phantom center (both channels together in phase), and L + R and L-R to check for the correct connection of your loudspeakers. Track 7 is a 1-kHz tone in both channels at 0 VU (actually the tone is 1,035 Hz and -10.4 dB). Tracks 8 through 20 are test tones from 20 Hz to 20 kHz, in both channels, at-10 dB below 0 VU reference; the booklet misstates the frequencies on tracks 8 through 11. Track 21 is a 440-Hz tone, which is an "A" for tuning instruments; again, this is misidentified. Track 22 is a re peat of track 7. Track 23 is pink noise, left and right. Track 24 is pink noise, in phase and out of phase. Track 25, "The Sound stage: Imaging, Depth, and Directionality," features a man moving to different positions in a large, very reverberant room and stating where he is with respect to the microphone. Tracks 26 through 30 have bass drum and cymbal sounds to check frequency response and dynamics. The lowest frequency from the bass drum is 37.5 Hz and at only -10 dB from the 0-dB d.c. reference level; the cymbal has energy beyond 16,250 Hz, where the level is -27 dB. Tracks 31 through 34 have the sound of a scraper in the left, right, and center so you can check how your system reproduces this complex sound and also check the system's transient response. Tracks 35 through 39 are musical excerpts. The final tracks, 40 through 45, are intended to help you set up a surround system. The last one is of a very good Dixieland band playing "Struttin' with Some Barbecue"; it has a good sense of space and ambience, with most of the instruments recorded relatively close except for the trumpet, which sounds distant.
Stereophile Test CD2 (Stereophile STPH 004-2) was produced by John Atkinson, the editor of Stereophile magazine. An informative, 26-page booklet accompanies this 31-track disc, which costs $7.95 plus $3 for shipping and handling. There are musical excerpts and test signals intended to help you identify and correct problems with your sound system as well as test signals in tended for use with both inexpensive and expensive test instruments. Tracks 1 and 2 are for channel identification and phasing. Tracks 3 through 9 are musical excerpts. At 19 seconds into track 4, there is a -40 dB thump with a spectrum from 15 to 30 Hz, a good test for true subwoofers. Track 10 features Larry Archibald, the publisher of Stereophile, talking and clapping as he walks around, "mapping out" the sound of a recording venue; tracks 11 and 12 are piano selections performed in this same hall and using the same figure-8 coincident microphone pair. Track 13 is from Edward El gar's "The Dream of Gerontius" and features a soloist with chorus and orchestra. Track 14 is "Eden," composed and per formed by Corey Greenberg, a former contributor to Stereophile, in a studio using guitar sounds and artificial reverberation; 15 seconds in, there is a bass sound that reaches down to 30 Hz. Tracks 15 through 31 are test signals for evaluating system performance.
The first 42 seconds of pink noise on track 15 is correlated (i.e., the same in both channels), so that it should produce a clear, centered front image and no sound from the rear channels of a surround system. The pink noise on the remainder of this track is uncorrelated in the left and right channels and should produce a wide spread of sound with no specific central image; if you have a surround system, the sound should come from all of your speakers at the same level. Tracks 16 through 18 contain warble tones for the bass decade (descending from 200 to 20 Hz), the midrange decade (ascending from 250 Hz to 2 kHz), and the treble decade (ascending from 2.5 to 20 kHz). Track 19 has an interesting "Music Articulation Test Tone" by Arthur Noxon of Acoustic Sciences Corp.; it can be used to determine the resolving power of your system. Tracks 20 through 25 contain demonstrations of different types of distortion. Track 26 is claimed to have three index points. The signal at index 2 is supposed to demonstrate the effects of jitter by applying a 4-kHz modulation to an 11-kHz tone; I could only find index 1, a pure 11-kHz tone. Tracks 27 through 29 are meant to test CD players and tape recorders. Track 30 has 19- and 20-kHz tones at 0-dB reference level (I measured each tone as actually being at -6.5 dB); these tones are to be used with a spectrum analyzer to test for IM distortion. The last track, 31, also intended for use with a spectrum analyzer, has a 20-kHz tone at 0 dB (I measured this tone as -0.4 dB).
If I had to pick only one of these four CDs, I would be in a real quandary. The Sheffield/Coustic disc has music by Clair Mario on tracks 2 and 4 that I have used for demonstration for a number of years, the invaluable absolute polarity test, plus surround system test signals. The Sheffield/ XLO disc has a very good "walkaround" test on track 3, the "clap" on track 4, the intriguing demagnetization signals on tracks 6 and 7, and an "M-S" (mid-side) microphone recording of the Los Angeles Philharmonic on track 10. The ESX disc has a very good test on track 25 to check for imaging, depth, and directionality; excellent bass drum, cymbal, and scraper sounds on tracks 27 through 34, and some surround tests on tracks 40 through 45. The Stereophile CD has a tremendous variety of music and test signals intended for listening and measuring. I am certain that I will be using this disc to correlate subjective comments from my listening panel with objective measurements I make with my lab instruments. I hope that I have de scribed these CDs well enough for you to make a choice. As for me-I'd buy all of them!
-Edward M. Long
(Audio magazine, Jan. 1995)
Also see:
Two Test CDs -- Auditory Demonstrations and Anechoic Orchestral Music Recording (Auricle, July 1989)
Telarc OmniDisc Test Record (Feb. 1983)
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