OWNERS MANUAL FOR WEISS DAC202 D/A CONVERTER
Page
7
Date: 03/10
In the standalone D/A converter jitter can be introduced
by inferior cables between the source (e.g. CD transport)
and the 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 pathes 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 beeing 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 which 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
