Bryston BCD-1 CD Player User Manual


 
SonIc SuPERiORiTY
3
ADVANTAGE
The advantage of an all in one box solution for a CD Player
(as opposed to a separate outboard DAC and Drive) is the
elimination of jitter. For optimum performance the Drive
and DAC must use the same MASTER CLOCK. If the
clock signal of the drive is not synchronized with the clock
signal from the DAC then jitter develops. In external DACs
the digital input must be re-clocked in order to reduce the
jitter. Jitter is defined as mistiming of the digital signal. The
timing of all those ones and zeros is of extreme importance.
It isn’t enough to get the bits right; those bits have to be
converted back into music with the same timing reference
as when the music was first digitized. These timing errors
(jitter) are the bane of quality audio. With the Bryston
CD player the master clock and the drive are synchronized
perfectly to eliminate any possibility of jitter affecting the
sound quality of the player.
BRYSTON DAC
The DAC integrated circuit (chip) provides the conversion
of the digital signal to the analog domain. The chip used in
the BCD-1 CD Player is a Crystal CS4398. The CS4398
is a hybrid multi-bit delta-sigma DAC. This is a rather
tongue-twisting description that refers to an advanced
generation chip using a combination of several different
methods to optimize the conversion process. This DAC
uses a process to over-sample the digital input 128 times.
Over-sampling is when the samples are re-read (2x, 4x, 8x,
etc.) to create a new sampling frequency. The new samples
are then run through an interpolation filter to create a more
analog-like waveform. The output of this process is a very
sensitive analog signal and it is critical that the timing of
this process is very closely controlled by a low jitter clock.
DAC chips also require a very clean digital power supply
if they are to function at their optimum. Noise on the
digital supply may cause added jitter, noise, and distortion.
Incorrect circuit trace routing of the digital power supply
or ground may introduce digital noise into the analog
circuits. This digital power supply is provided from a
separate closely regulated and filtered source. The DAC
also requires a high quality analog power source because the
analog signal is at its lowest magnitude when it enters and
leaves the DAC. As a result, any added noise or distortion
will be greatly amplified by later stages. Again a separate,
heavily regulated and filtered power supply with carefully
routed grounds is provided. Finally, if a digital trace, signal
or power, is routed in a layer above or below an analog trace
it can induce noise via capacitive coupling. Careful trace
routing eliminates these problems and provides the extra
dB’s of noise and distortion reduction which separates good
from outstanding equipment. This attention to detail with
the power supplies is one of the reasons for the superior
sound of the BCD-1 Bryston CD Player.