funkstar;459635 Wrote:
> This is correct. The -only- place jitter can occur is between the player
> and the stereo, nothing before, (from the hard drive, to the PC, to the
> network to the player) can introduce or have an effect on jitter .
It is true that nothing can add jitter before the player, but once a
signal is in the analog domain, jitter (i.e., rapid variation of group
delay in the audio band) is hard to introduce in reasonbly designed,
linear circuits operating with well-regulated power supply rails.
The place where jitter is most likely to be introduced is at the point
where digital samples are converted to analog i.e., in the DAC. Any
modulation of the effective DAC clock signal edge transitions will have
the effect of causing phase/frequency modulation of the every sinewave
that comprises the overall music signal.
Code:
--------------------
V(k) = A0*sin(2*pi*f0*k*(T+dTJ(k)))
--------------------
V(k) is the kth sample of a sinewave of nominal frequency f0 to be
reproduced, from T-spaced PCM samples, where the time between samples
(typically 1/44100 seconds) is modulated by some time-variant jitter
represented by dTJ.
The equivalece to an FM waveform can be seen by rewriting the equation
as follows:
Code:
--------------------
V(k) = A0*sin(2*pi*k*T*(f0+f0*dTJ(k)/T)))
--------------------
dTJ(k) can be deterministic in nature (e.g. a 60Hz sinewave due to
imperfect power supply regulation), data related (different bit patterns
cause the clock edge to be early or late to different degrees) or random
(residual phase noise on the clock signal) or a combination of all
three.
I am not going to get into the religious/tribal invective about how
much jitter matters.
--
dsdreamer
----------------------
"Dreamer, easy in the chair that really fits you..."
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