15
DVD Technical Notes
Audio
Organizing the data into left and right pulse streams is the job of
the DSD decoder. A Sony-built LSI, the DSD decoder first reads
the invisible watermark — a key anti-piracy feature — and then
decodes the incoming data. Data on the disc originate as
alternating bursts of left-channel and right-channel information.
Buffer memory and master clock sync enable the bursts to be
output as two
continuous,
simultaneous
streams. The DSD
decoder also reads
sub code data,
including text and
Table of Contents
information such
as track number
and playing time.
To preserve the maximum accuracy of the DSD pulses, our
design program identified two basic goals:
• Amplitude axis precision
• Time axis precision
Sony’s Accurate Complementary Pulse Density Modulation (ACP)
system and Current Pulse D/A Converter meet the first goal.
Sony’s new pulse generator in VC24 achieve the second goal.
The Megahertz switching speeds of DSD decoding have an
unfortunate byproduct, switching glitches, rough irregularities in
the DSD pulse train. Sony’s Accurate Complementary Pulse
Density Modulation (ACP) overcomes this by converting the
DSD pulses. Instead of encoding 1 as a pulse and 0 as the
absence of a pulse, ACP represents each digital 1 as wide 1
followed by a narrow 0. And ACP represents each digital 0 as a
narrow 1 followed by a wide 0. In this way, ACP effectively
converts the data from pulse height (sensitive to glitches) to
pulse width (insensitive to glitches). So glitches are not passed
along to subsequent circuitry.
Conventional D/A converters generate pulse height from the voltage
power supply — a method that can expose the signal to subtle
power supply voltage fluctuations. The Current Pulse Converter
overcomes this limitation. The design changes the incoming train of
voltage pulses to a train of current pulses. Because the circuit
incorporates an extremely clean “constant current” source, the
pulses emerge with the desired flat tops, flat bottoms and identical
height. You get audio output of extraordinarily low distortion. The
Current Pulse D/A converter operates for SACD, CD and DVD-
Video sound tracks alike. The system supports the highest sound
quality in DVD-Video: 96 kHz/24-bit recording.
A conventional digital filter has a fixed filtering coefficient with
no user controls. Sony’s Variable Coefficient digital filter is a
dramatic departure. The VC digital filter actually offers different
settings, representing different filter coefficients, different
filtering methods and different objectives in reproduced sound.
After current-to-voltage conversion, a simple low-pass filter is
all that’s required to produce an analog output. Unlike CD, the
SACD cutoff frequency is largely determined by the characteris-
tics of the player’s low-pass filter. The DVP-S9000ES low-pass
filter has aresponse
curve that slowly
falls in the vicinity
of 50 kHz,
enabling usable
response out to
100 kHz, some
five times higher
than previous
home audio
sources.
As an audio/video player, the DVP-S9000ES needs to generate
master clock frequencies for audio and video simultaneously.
Typical practice deploys a Phase Locked Loop (PLL) circuit to
subdivide the video master clock for audio use. However, this
exposes the audio signal to unwanted jitter, which can generate
audible distortion. That’s why the DVP-S9000ES subdivides
audio master clock for video use. The SACD and CD master
clock runs at 44.1 kHz x 1024 = 45 MHz. The DVD-Video sound
track master clock runs at 48 kHz x 1024 = 49 MHz. And the
DVD-Video clock for pictures downconverts this via PLL to
DSD Decorder
Photo 3: The heart to SACD reproduction, Sony’s DSD
decoding LSI.
ACP System
Fig.17: Thanks to Pulse Density Modulation, the ACP system
disregards amplitude distortions and switching glitches.
96 kHz / 24-bit capable Current Pulse
D/A Converter ( for all discs )
VC 24 Plus Digital Filter ( for DVD-Video and CD )
Fig. 18: The Low Pass Filter of the DVP-S9000ES enables
usable frequency response to 100 kHz, some five times higher
than previous home audio sources.
Two Audio Master Clocks ( for all discs )
Separate Low-Pass Filters ( for all discs )
