My review of the UltraBit Platinum CD treatment in the August issue of The Absolute Sound understandably generated some controversy. I say â€œunderstandablyâ€ because itâ€™s hard to imagine a mechanism by which a fluid applied to a CDâ€™s surface could affect sound quality, never mind introduce an analog-like variability in such aspects of the sound as timbre and soundstaging.
I donâ€™t know how UltraBit Platinum (or any other CD treatment) works, but I have first-hand experience that suggests that a CDâ€™s optical properties can affect the sound in an analog-like manner even though the datastream remains unchanged.
In the late 1980s, I worked in a CD mastering lab. In addition to being part of a six-man team that designed and built CD (and Laserdisc) mastering machines, my job included correlating problems in replicated discs with anomalies on master tapes and the mastering process. (I co-wrote, with Ray Keating, an Audio Engineering Society paper on this subject called â€œCD-V Signal Optimization.â€)
A CD-replication client claimed that the discs we made sounded inferior to his master tape. I performed a bit-for-bit comparison between the master tape (3/4â€ U-Matic tape in the PCM-1630 format) and the replicated disc using a CD-ROM pre-mastering computer. Not surprisingly, the data were bit-for-bit identical. I was unable to verify the clientâ€™s claim that the disc sounded different from the master because I couldnâ€™t listen to both sources through the same D/A converter.
My colleaguesâ€”all â€œbits is bitsâ€ engineersâ€”dismissed the clientâ€™s claim as mere delusion in light of the bit-for-bit accuracy of the disc to the master tape. In their view, we had done our job in delivering a CD with a bitstream that was identical to the master.
Nonetheless, I wanted to pursue this question, and cut another master from the same tape, but on a different mastering machine. The client reported that the discs made from this second master sounded significantly better than the first discs. With two CDs, I could now compare them for myself decoded through the same D/A converter. The client was correct; the second CD sounded smoother, more spacious, and less â€œdigital.â€ He didnâ€™t describe the differences in those terms; to him, the first disc was simply missing his musical expression.
There were no manufacturing differences between the discs; neither had uncorrectable errors or other problems that are routinely checked during QC. My curiosity was piqued, so I had the jitter on both discs analyzed using a specialized piece of test equipment. To understand the concept of jitter in a CD, some background on how the CD works is necessary.
Digital data are stored on the CD in â€œpitsâ€ (indentations in the disc) and â€œlandâ€ (the flat disc surface). The transition from pit-to-land or land-to-pit represents binary â€œone.â€ All other surfaces (pit bottom or land) represent binary â€œzero.â€ The pit and land structures donâ€™t represent the data directly. Rather, an encoding scheme called â€œeight-to-fourteen modulationâ€ (EFM) creates patterns of data in which successive binary â€œonesâ€ are separated from each other by a minimum of two â€œzerosâ€ and a maximum of ten â€œzeros.â€ This produces nine discrete pit and land lengths on the disc.
The playback laser beam is reflected from the disc to a photodetector that converts light to an electrical signal. The nine discrete pit and land lengths produce a amplitude-modulated signal at the photodetector composed of nine discrete sinewaves, which vary in frequency from 196kHz (corresponding to the longest pit or land length) to 720kHz (corresponding to the shortest pit and land lengths). The digital data are contained in the sinewavesâ€™ zero-crossing transitions.
The jitter analyzer counts the exact frequency of each of the nine sinewaves, and then graphically plots their frequency distribution. The distribution is Gaussian, with most of the pit and land lengths falling very close to the ideal. On the first disc, the distribution was extremely wide, with large variations in the pit and land lengths. On the second disc, the distribution was sharply defined and the curve was very narrow. In other words, the first disc had a greater amount of jitter encoded in the physical structures that represent the digital data. You could see this by looking at the signal from the photodetector; the so-called â€œeye patternâ€ was a little ragged on the first disc compared to that of the second disc. (Thereâ€™s a reason the second disc had lower jitter; the mastering machine on which it was cut had a more sophisticated rotational-servo control than that of the first mastering machine.)
Note that the pit- and land-length variations were not great enough to be interpreted incorrectly; a binary â€œoneâ€ was never mistaken for binary â€œzero.â€ The datastreams were identical after decoding. Similarly, the eye pattern from a CD-R is significantly cleaner looking than that of a replicated CD, although the data remain unchanged. Virtually everyone who has compared a CD-R to the CD from which it was burned reports that the CD-R sounds better than the original.
Itâ€™s clear to me that the quality of the signal at the photodetector affects the discâ€™s sound. I donâ€™t know how variations in the eye pattern find their way into the analog output signal; the photodetectorâ€™s output undergoes a huge amount of decoding, error correction, de-interleaving, and other processes to extract the raw PCM audio data that are converted to analog by the DAC. Nonetheless, thereâ€™s no question in my mind that a discâ€™s optical properties, which directly influence the eye pattern, introduce an analog-like variability in sound.
It is not such a great leap of faith to suggest that a fluid applied to the disc could introduce the kinds of sonic differences I heard in the listening room after applying UltraBit Platinum. Itâ€™s a mistake to dismiss what your ears tell you because the phenomenon in question cannot yet be explained.