STATE-OF-THE-ART

The Bryston BDA-1 is a state-of-the-art external Stereo DAC (digital to analog converter) using fully discrete Class-A

proprietary Bryston analog circuits, two independent linear power supplies and dual Crystal CS-4398 DAC chips. The BDA-1

features an impressive array of inputs for USB, COAX, OPTICAL, AES-EBU and BNC equipped digital devices.For audio

outputs, the BDA-1 offers both balanced XLR as well as unbalanced RCA stereo connectors on the rear panel. The BDA-1

is RS-232 software upgradeable, making it the most flexible high performance DAC on the market.

 

JITTER REDUCTION

Jitter is a mistiming of data being moved from point A to point B in any synchronous digital system. Think of jitter as

individual ticks on a clock—however each tick is not occurring at exact one-second intervals. Some are slightly less than a

second and some are slightly longer, and they average out so that no actual time is being gained or lost over a large

number of seconds. Jitter is the difference between the shortest and the longest second, and in digital audio systems this

specification is usually measured in nanoseconds. Both the frequency and the jitter characteristics of the system’s digital

clock will affect the accuracy of reproduction. The frequency, if not accurate, can cause the pitch and speed of the music

to change, and in some systems cause drop-outs if there is no data available.

 

THE BRYSTON SOLUTION

Bryston delivers superb sonic performance by re-sampling and re-clocking the digital input in order to reduce jitter. The

result, a significant reduction in jitter (1/1000 of a nanosecond). But it isn’t enough to just 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. The input signal of

the BDA-1 is re-clocked and re-sampled to reduce any possibility of jitter affecting the sound quality. Even the input

receiver and the sample rate converter serve to further reduce jitter.

MPEDANCE MATCHING TRANSFORMERS

The best way to understand the Bryston BDA-1 External DAC is to follow the flow of a signal from when it first arrives at the

BDA-1 in digital form to when it leaves to drive an external analog input. The digital signal first arrives at the BDA-1 via either

the SPDIF COAX, OPTICAL OR AES EBU inputs or the USB interface input. These are the standard digital outputs from a CD

Drive, Sound Card, Computer, Music Server etc. There are 6 digital inputs, which are easily selected using a front panel

switch. This digital signal contains data at over 1 million bits per second that requires a bandwidth of 5 to 10 million hertz

(cycles per second). At these high frequencies, it is very important to maintain the quality of the signal by having the

correct termination at the digital inputs. The BDA-1 provides for this termination in the best possible manner using devices

called impedance matching transformers. Impedance matching transformers provide the optimal interface to the incoming

source under all sorts of signal conditions. Lesser quality terminations will degrade the signal, causing increased jitter.

 

UPSAMPLING

After the input stage, the signal goes to the SYNCHRONOUS upsampling circuit (sample rate converter). This circuit

converts the digital signal from one sample rate and bit depth to another. In the BDA-1, the sample rate is increased from

the input sample frequency (32K, 48K, or 96K upsamples to 192K and 44.1K or 88.2K upsamples to 176.4K). The 16 bits of

depth (the CD standard) is increased to 24 bits. The added 8 bits are filled with placeholder information. This upsampling

process provides a digital signal for later conversion to analog by the Crystal 4398 DAC chip. The upsampling process

doesn’t add any new, but does put the data in a form which can better be translated by the DAC as described below.

The advantage of this synchronous upsampling process is improved processing of the upsampled signal by the DAC chip,

which was designed for higher sample rates and bit depths. There is also a noise shaping process implemented where

“noise” within the audible spectrum is shifted up to frequencies above audible limits. An added advantage of this

upsampling process is that a totally new clock signal is applied, which results in significant jitter reduction.