Bryston CD Player:
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.