landmark CDP-X77ES in 1990 and has since been followed by Sony's Current Pulse 1-bit converter. Like other 1-bit converters, these Sony® designs overcame the problem of zero-cross distortion, achieving superb low-level linearity for excellent sound, even during quiet passages and the reverberant tails at the end of musical notes.
1 bit D/A conversion (Current pulse)
On/off
1
The principle of 1-bit D/A conversion. In order to reproduce Super Audio CD, Pulse Width Modulation must operate at a higher frequency than the SA-CD sampling frequency of 64 fs (equal to 2.8224 MHz).
These 1-bit converters performed beautifully and dominated CD player design throughout the 1990s. However, in order to avoid the influence of jitter, to maintain linearity in the time axis, 1-bit converters need to be driven by a highly precise clock. And Super Audio CD makes this demand for precise timing even more stringent. Super Audio CD uses an extremely high sampling rate of 2,822,400 samples per second—2.8224 MHz. Many 1-bit converters employ Pulse Width Modulation, in which the converter modulates the output by creating longer or shorter pulses. Unfortunately, this requires a D/A converter clock frequency substantially higher than 2.8224 MHz. Because it's extremely difficult to maintain clock precision at such high frequencies, the signal is exposed to time-axis errors—jitter—which pass directly into the analog audio waveform, causing subtle distortion.
Such distortion was not acceptable for the design program of the ES Series DVD players. That's why Sony® ES engineers endowed the SA DAC with Sony's multi-level D/A conversion. Unlike the multi-bitconversion used at the dawn of the digital age, multi-levelconversion exhibits superb low-level linearity. And unlike the 1-bit conversion, multi-level conversion is remarkably free from jitter and jitter-induced distortion. You get the best of both worlds.
The multi-level D/A system has multiple switches controlling multiple current sources—in effect a number of 1-bit digital-to-analog converters operating in parallel. The analog output is created by summing all the current sources. Unlike 1-bit DACs, output is expressed not by the pulse width but the number of the current sources. This reduces the clock frequency, reducing the influence of clock jitter and reducing the radiation of noise into nearby circuits.
ES DVD Players 2005, Version 4.0 | Page 33 |
1 /64fs 
1 /64fs
1 /64fs 
