CD Direct Master clock
Generator Technology.
In a CD-player one of the most
important parts is the master
clock signal. The master clock
is controlling the rhythm of the
CD-player by telling the DAC
chip exactly when to convert the
audio signal from digital to
analog. To have the best
possible sound, it is vital to
have a master clock that has a
very stable clock frequency and
lowest possible jitter.
Jitter is timing errors in clock
generator circuits. A master
clock generator should have a
very stable time period. If the
timing period of the master
clock generator is moving back
and forth in time this timing
error is called jitter. Jitter
for a clock generator is
measured in pico seconds, and
the number of pico seconds of
timing jitter is a measure for
the quality of the clock
generator. To have the best
possible sound, it is best to
have a lowest possible jitter
value.
All Hegel CD-players have less
than 10 pico seconds of jitter.
There are many mechanisms that
can generate jitter in a master
clock generator: power supply
noise, clock oscillator topology,
quality of quartz crystal
resonator, clock driver circuit
and circuit board layout.
Most CD-players are using a
master clock located at the CD
servo-decoder board in the
CD-player. Because the
servo-decoder board has got a
lot of high- and low frequency
noise from the CD servos and the
digital CD decoder circuits this
is not a good solution. A Master
clock generator on the CD
servo-decoder board will have an
unstable frequency and high
jitter because of the high
levels of signal noise and power
supply noise on this board. In
addition to having the Master
clock generator on the CD
servo-decoder board , many
CD-players are also using a
SPDIF serial digital interface
from the CD servo-decoder board
to the DAC-board, and this will
give decreased sound quality
because of digital audio data
related jitter.
The most expensive CD systems
are using a separate Master
clock generator that is
connected to the CD
servo-decoder and to the DAC
board. This is an expensive
solution, but will always give
the best sound. All Hegel
CD-players are using a very high
precision Master clock generator
with extremely low jitter, and
this Master clock generator is
located on the DAC board inside
the CD-players. This high
precision Master clock is
distributed directly to the DAC
chip and directly to the CD
servo-decoder board. In this way
the performance of the Hegel
master clock generator is
equivalent to very expensive
CD-systems. |