Technical data

OWNERS MANUAL FOR WEISS DAC202 D/A CONVERTER
Page 4 Date: 03/10
2007 Introduction of the CASTOR, our High-End Hi-Fi Power
Amplifier
2008 Introduction of the MINERVA Firewire DAC and the VESTA
Firewire – AES/EBU Interface
2010 Introduction of the DAC202 Firewire DAC, the INT202
Firewire Interface and the ATT202 Passive Attenuator
ADVANCED DIGITAL AND ANALOG AUDIO
CONCEPTS EXPLAINED
Jitter Suppression and Clocking
What is jitter and how does it affect audio quality? In the audio
field the term jitter designates a timing uncertainty of digital
clock signals. E.g. in an Analog to Digital Converter (A/D) the
analog signal is sampled (measured) at regular time intervals;
in the case of a CD, 44100 times a second or every 22.675737..
Microseconds.
If these time intervals are not strictly constant then one talks of
a jittery conversion clock. In practice it is of course not possible
to generate exactly the same time interval between each and
every sample. After all, even digital signals are analog in their
properties and thus are influenced by noise, crosstalk, power
supply fluctuations, temperature etc.
Hence a jittery clock introduces errors to the measurements
taken by the A/D, resulting from measurements being taken at
the wrong time. One can easily observe that the level of the
error introduced is higher during high audio frequencies,
because high frequency signals have a steeper signal form.
A good designer takes care that the jitter amount in his/her
design is minimized as well as possible.
What type of equipment can be compromised by jitter?
There are three types: The A/D Converter as described above,
then there is the D/A Converter where the same mechanism as
in the A/D Converter applies and the third is the Asynchronous
Sample Rate Converter (ASRC). The ASRC is not something
usually found in Hi-Fi systems. It is used by Sound Engineers to
change the sample rate from e.g. 96kHz to 44.1kHz, or e.g.
for putting a 96kHz recording onto a 44.1kHz CD.
You may now argue that in High-End Hi-Fi there are such things
as „Oversamplers“ or „Upsamplers“.
Yes, those are in essence sampling rate converters, however in
a well-designed system these converters employ a synchronous
design, where jitter does not play any role. Of course a
conversion between 96kHz and 44.1kHz as in the example
above, can be done in a synchronous manner as well. An ASRC
in fact is only required either where one or both of the sampling
frequencies involved are changing over time („varispeed“ mode
of digital audio recorders) or where it is unpractical to
synchronize the two sampling frequencies.
So basically in Hi-Fi jitter matters where there are A/D or D/A
converters involved. CD and DVD players are by far the most
numerous type of equipment employing D/A converters. And of
course stand-alone D/A converters. Jitter, being an analog
quantity, can creep in at various places. The D/A converter built
into CD or DVD players can be „infected“ by jitter through
various crosstalk mechanisms, like power supply contamination
by power hungry motors (spindle / servo) or microphony of the
crystal generating the sampling clock or capacitive / inductive
crosstalk between clock signals etc.
In the standalone D/A converter jitter can be introduced by
inferior cables between the source (e.g. CD transport) and the