Hi Stu,
I think this jitter thing is one of the areas that is the most misunderstood. You can not get rid of jitter - you can only reduce it a bit. To reduce it you are 'playing' with the bitstream which in my opinion is maybe not the best option (I think the more you fiddle the more you can screw it up). The jitter numbers on the CD player are at very low levels because you can clock the 'DAC' directly to a 'KNOWN' bitstream from the 'Drive' through a 'Master Clock' and reduce jitter substantially. By the way the closer the DAC is to the Master Clock the better. In an outboard DAC you have to re-clock and re-sample so generally there is potential for more jitter because the incoming bitstream is 'unknown'.
So in my opinion if you want to achieve the highest quality playback with the least amount of jitter then start with a low jitter source device. In the BDA-1 DAC the best playback 'currently' is achieved with a quality 'high-resolution' (44.1/16Bit to 192K/24Bit) soundcard (with low jitter and low latency) in a computer based system fed into the BDA-1's BNC/SPDIF or AES-EBU input. Inputs such as Optical generally will exhibit higher jitter numbers than SPDIF.
There are products on the market that will allow USB or Optical to output SPDIF and try to reduce jitter but the Bryston DAC was not aimed at that market segment. In the BDA-1 synchronous upsampling does not result in a reduced jitter figure. I am not an expert on this but asynchronous upsampling can be used to try and reduce jitter but it just masks input-side jitter from appearing in the output signal, by converting time-domain errors into amplitude domain errors which will not show up as jitter components per-se. The BDA-1 upsamples the actual input signal data; it doesn't synthesize a new data set derived from the input signal, as do DACs with asynchronous upsampling. The BDA-1 is an attempt to provide the best possible performance if you have the quality sound card and use the appropriate inputs. For instance, the USB input on the BDA-1 eliminates one digital conversion by using I2S (not spdif) at it's input which is the NATIVE bitstream and then we run it through a 'SYNCHONOUS' (less digital math to screw things up) sampler- if you engage the up-sample button on the front of the BDA-1.
Also recognize that many tests have been done with jitter indicating what is actually heard by experienced listeners are much higher numbers (in the order of 10 times as much) than most good quality digital gear is putting out. So in the BDA-1 DAC we found that the quality and integrity of the power supplies, separate digital and analog power supplies, separate ground planes for digital and analog sections, discrete class A analog circuits etc far outweigh the slight increase in jitter numbers comparing the CD Player with the BDA-1 DAC.
I recognize that many people have to make their decisions on what DAC they will use based on their source gear (CD Player drive, Laptop with USB or optical, Streaming devices etc.) but if you want state of the art playback at this point in time then the computer based high-resolution soundcard connected appropriately to the BDA-1 is the direction to head. The beauty of the Bryston BDA-1 DAC is that it gives you a central point into which you can plug in up to 8 digital sources and achieve the highest performance available from the device feeding it.
Wow this got away from me -- sorry did not mean for this to be this lengthy!
james
