Technical data

OWNERS MANUAL FOR WEISS DAC202 D/A CONVERTER
Page 5 Date: 03/10
D/A converter unit or by the same mechanisms as described
above except for the motors of course.
In the case of a stand-alone D/A converter (as the DAC202),
one has to take two different jitter contamination paths into
account.
One is the internal path where internal signals can affect the
jitter amount of the sampling clock generator. Here, all the
good old analog design principles have to be applied. Such as
shielding from electric or magnetic fields, good grounding, good
power supply decoupling, good signal transmission between the
clock generator and the actual D/A chip.
The other path is the external signal coming from the source to
which the sampling clock has to be locked. I.e. the D/A
converter has to run synchronous to the incoming digital audio
signal and thus the frequency of the internal sampling clock
generator has to be controlled so that it runs at the same
sampling speed as the source (e.g. CD transport). This
controlling is done by a Phase Locked Loop (PLL), which is a
control system with error feedback. Of course the PLL has to be
able to follow the long term fluctuations of the source, e.g. the
sampling rate of the source will alter slightly over time or over
temperature, it will not be a constant 44.1kHz in the case of a
CD. But the PLL should not follow the short-term fluctuations
(jitter). Think of the PLL as being like a very slow-reacting
flywheel.
In the DAC202 we employ a two-stage PLL circuitry, which very
effectively suppresses jitter. A common problem with most PLLs
used in audio circuitry is that they suppress jitter only for higher
frequencies. Jitter frequencies that are low (e.g. below 1kHz or
so) are often only marginally suppressed. It has been shown
that low frequency jitter can have a large influence on the audio
quality though. The DAC202 suppresses even very low
frequency jitter components.
This means that the DAC202 is virtually immune to the quality
of the audio source regarding jitter. For a CD transport as a
source this means that as long as the data is read off the CD in
a correct manner (i.e. no interpolations or mutes) you should
hardly hear any difference between different makes of CD
transports or between different pressings of the same CD. Also
„accessories“ like disk dampening devices or extremely
expensive digital cables will not make any difference in sonic
quality. Of course it is always a good idea to have a good
quality cable for digital (or analog) audio transmission - but
within reason.
Upsampling, Oversampling and
Sampling Rate Conversion in
General
In consumer audio circles the two terms oversampling and
upsampling are in common use. Both terms essentially mean
the same, a change in the sampling frequency to higher values.
Upsampling usually means the change in sampling rate using a
dedicated algorithm (e.g. implemented on a Digital Signal
Processor chip (DSP)) ahead of the final D/A conversion (the
D/A chip), while oversampling means the change in sampling
rate employed in today’s modern D/A converter chips
themselves.
But let’s start at the beginning. What is the sampling frequency?
For any digital storage or transmission it is necessary to have
time discrete samples of the signal, which has to be processed.
I.e. the analog signal has to be sampled at discrete time
intervals and later converted to digital numbers. (Also see
"Jitter Suppression and Clocking" above)). This sampling and
conversion process happens in the so-called Analog to Digital