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- 78 posts total
It should not. Bits are bits. However, noise from servo motors (reading the disk) can induce modulation distortion back through the power supply and create a jittery input to the internal DAC. There is also logic induced modulation that may affect the internal DAC. And then how the internal DAC does conversion. So in practice differences can be substantial listening to the analog out of different transports. If you are taking a digital feed from the transport then it is the jitter that is inherent in that digital signal which might affect whatever DAC is downstream. If you get a DAC with complete jitter rejection (below audibility) and then all transports played to that DAC will sound the same because as you said yourself, apart from clock timing (jitter), it is all 1s and 0s. |
Actually it’s not 1s and 0s. It’s not 1s and 0s until the data gets to the A to D converter. The laser is simply reading ON and OFF depending on whether the laser beam is hitting a pit or land. Actually the laser reading process is an analog process, not digital. Also, the length of the lands, which are variable, helps determine what the actually digital data is. There are several problems that make the reading of the “data” on the CD imperfect. One is wobbling of the CD due to out of round condition, various types of vibration and/or not being absolutely level during play. Another is background scattered laser light that makes its way into the photodetector. The photodetector is kinda stupid and can’t tell the difference. Yes, I know what you’re thinking, “But the Reed Solomon Error program is supposed to take care of all that.” |
The operative word here is JITTER. Jitter is the variability in the timing of the bits coming out the end of the S/PDIF cable from the CD transport. At 44.1kHz sample-rate, the bits frequency is around 2.8MHz. ANY variability in the timing of these bits, one bit to the next bit, will cause the D/A conversion to be distorted. The output voltage will not be at the correct value at each point in time, creating analog distortion. Jitter in a typical CD transport is caused by: 1) inaccurate reads of the pits because of imperfect disk and vibration in the disk while spinning - this can be improved by re-writing on a good CDROM disk and by applying treatments to the disk. Some older disk players used a platter like a turntable to eliminate the vibration. 2) jitter in the internal Master Clock oscillator - selected by the designer 3) power subsystem deficiencies that power the oscillator and associated circuits due to the design 4) imperfect S/PDIF output driver due to the design 5) imperfect S/PDIF cable - get the best one you can afford When one refers to a CD player as a "Transport", it means they are using the digital output over a S/PDIF cable from the device, in conjunction with an external DAC or D/A converter. Here is a typical jitter plot from a transport: http://www.audiocircle.com/index.php?topic=154408.0 Here is how the S/PDIF cable adds jitter to the equation: http://www.audiocircle.com/index.php?topic=154425.0 You can see from these measurements what a Synchro-Mesh reclocker can do to reduce jitter from ANY transport or server. None of the disk treatments are needed if a Synchro-Mesh is used, and it provides galvanic isolation, breaking ground loops. Also, see how good a $275 S/PDIF cable can be. Steve N. Empirical Audio |
- 78 posts total