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After being connected to a transport, the Lens will show a number on the display's right-hand side. This number indicates the transport's speed accuracy, measured in Parts Per Million (ppm). We're not talking about the transport's jitter, but its average deviation from the standard output frequency. Because of crystal oscillator tolerances, some transports run slightly faster or slower than the correct frequency. The highest deviation Genesis has seen is 250ppm speed error, with 50ppm being a typical value. The Mark Levinson No.31 read 8ppm speed error, the Sonic Frontiers SFT-1 had 45ppm…
On the subject of the RAM delay, the Lens poses a problem for a Home Theater system: the audio will be out of sync with the video. Genesis addresses this problem with a "LaserDisc" mode that bypasses the RAM. Instead of using the memory for jitter elimination, a dual-PLL input receiver takes over to reduce jitter in the incoming datastream. This feature also lets you hear the effect on the reproduced sound of removing the RAM buffer.
The Lens gets its name from its function: focusing incoming data to a precise point at the Lens output circuit. That data could be jittered and have an…
All transports and jitter-reduction boxes Paul McGowan examined use an inverter gate to generate the negative-polarity or cold half of the AES/EBU output signal. Because all gates introduce what's called "propagation delay," the AES/EBU output's negative phase lags the positive phase very slightly (by the amount of the gate's propagation delay). This delay between phases reportedly introduced jitter in the digital processor the AES/EBU signal was driving. The new output driver chip subjects each phase to the same number of gates, thus introducing no time lag between phases. The difference in…
What I did enjoy, however, were the musical benefits of this higher resolution. Subtle nuances that were lost or barely hinted at without the Lens were suddenly vivid, palpable, and alive. Ralph Towner's superbly recorded acoustic guitar on Beyond Words had more inner detail of the kind that you hear from the live instrument. The Lens's superior resolution made the guitar more lifelike and real, and less like a canned reproduction.
In addition to revealing more timbral detail, the Lens also made instruments more separate and distinct. The presentation provided a greater impression of…
It didn't. The Mark Levinson No.31 still sounded better than the Sonic Frontiers SFT-1 and Parasound C/BD-2000, for the same reasons it sounded better without the Lens. Moreover, the SFT-1 was still more forward-sounding than the No.31 or C/BD-2000, and the Parasound transport's softish bass and more laid-back presentation remained with the Lens in the signal path. The Lens, however, reduced the magnitude of the differences between transports, leaving only traces of their musical characteristics. How the transports' jitter signatures got through the Lens's RAM and ended up at the DAC, where…
Sidebar 1: Specifications
Description: De-jittering device with "resolution enhancement" dither generation. Inputs: AES/EBU, RCA coaxial, BNC coaxial, TosLink optical, ST-Type optical. Outputs: AES/EBU, RCA coaxial, ST-Type optical. Display readout: CD subcode data (track time), transport speed accuracy (in parts per million), output word length (16 or 20 bits), dither mode, signal lock, input sampling frequency.
Dimensions: 19" W by 2" H by 8" D. Weight: 12 lbs.
Serial number of unit tested: 111115.
Price: $1800 (1996); no longer available (2003). Approximate number of dealers…
Sidebar 2: System
The Digital Lens spent most of its time in my system between the Mark Levinson No.31 transport and a Classé DAC-1 digital processor. The digital cable between the transport and Lens was the excellent Illuminati DataFlex Studio. An AudioQuest Diamond X3 AES/EBU cable connected the Lens to the Classé. This input/output digital cable complement was reversed depending on the digital processor's input options.
I also tried the Lens with the Sonic Frontiers SFT-1 and Parasound C/BD-2000 transports—two very different-sounding machines. Other processors I auditioned the…
Sidebar 3: Dither & Jitter
Dither: If you think about the literal meaning of the word dither—"a confused or agitated state"—you're halfway to understanding how dither works in digital audio. Dither is a small amount of noise added to the signal that makes digital behave (and sound) more like analog. This noise allows a digital system to resolve low-level information below the amplitude of its Least Significant Bit (LSB). Without dither, signals with amplitudes below the LSB are simply ignored by the quantizer; the signal never traverses two quantization steps, a requirement of…
Sidebar 4: Measurements
I approached the Lens measurements from two perspectives: its effect of jitter at the word clock inside a digital processor, and how it changed low-level waveforms with its dither-generation function. First the jitter.
Fig.1 is the Theta Chroma 396's clock-jitter spectrum made by driving the Chroma with a PS Audio Lambda transport playing the CBS Test Disc. The test signal was a 1kHz, -90dB undithered sinewave. We can see the now-classic spikes of jitter energy at 1kHz and its harmonics, the result of the test signal creating interface jitter. The RMS…
John Atkinson wrote about the Lens in October 1996 (Vol.19 No.10):
As impressive as I had found the original Mark Levinson No.31 CD transport, after about two years of living with it I found myself experimenting with outboard jitter-reduction units. In chronological order, I tried the Digital Domain VSP, the Sonic Frontiers UltraJitterbug, the Audio Alchemy DTI•Pro and DTI•Pro 32, the Meridian 518, and the Genesis Digital Lens. The sonic changes wrought by these devices were mainly positive, though the effect of the original DTI•Pro's enhancement algorithm was very dependent on the CD…