Studio Magazin

5 | 31 Studio Magazin 11/13
to the factory setting. To this end, you
keep the ‘Menu’ button pressed during
the power up.
Installation and Wiring
It should be understood that for a func-
tioning synchronization bond, all invol-
ved devices have to be connected care-
fully and with the shortest possible ca-
ble runs. For the transmission of Word
Clock signals, unbalanced BNC cables
with an impedance of 75 ohms are re-
quired. I found the hint in the manual
that these cables are normally referred
to as RG-59U or RG59B/U. In addition,
make sure that the WLCK inputs have a
75 ohm terminating resistor. Most WCLK
input channels feature a switchable re-
sistor (including the MC3+ via internal
jumper). For devices without a 75 ohm
terminating resistor, one uses an addi-
tional BNC T-piece allowing the connec-
tion of a physical connection resistor.
However, this should not be used to
loop through a WCLK signal so as not to
violate the signal integrity. Is there no
alternative connection option, all WCLK
inputs except the last device in the
chain should not be terminated. Never-
theless, the manufacturer refers that it is
not recommended to connect more than
three devices in series with a WCLK out-
put. Balanced XLR cables with an impe-
dance of 110 ohms are recommended to
connect AES/EBU or S/P-DIF interfaces.
In our experience, however, most XLR
studio cables anyway fulfill these requi-
rements. S/P-DIF connections are ma-
de via unbalanced Cinch/RCA cables wi-
th 75 Ohm impedance. When connecting
an optical cable (Toslink plastic), by the
manufacturer’s reference a length of 10
metres should not be exceeded. ‘True’
glass fiber optical cables allow even gre-
ater distances.
Re-clocking
Besides the fact that all externally re-
ferenced modes always lead to a rege-
neration of the output clock signal, the
MC-3+ additionally provides the alrea-
dy mentioned re-clocking or re-timing
function of an incoming digital audio si-
gnal. In this application, it is primari-
ly an optimization in sound of the DA
converter‘s reproduction. All three digi-
tal audio inputs (S/P-DIF coaxial and op-
tical, as well as AES3) can be accessed
in this mode. The re-timing produces a
phase-synchronous, completely re -ge-
nerated clock signal of the highest qua-
lity that is embedded in the output si-
gnals with the sampling rate of the digi-
tal audio input signal. To our knowledge,
the asynchronous re-clocking is current-
ly only possible with the MC-3+ Smart
Clock. In this mode, additional functions
are available. If you select one of the
available digital audio inputs, two fur-
ther options are offered by pressing the
‘Select’ button again: the selected in-
put plus WCLK or the selected input plus
10 MHz. Choosing these re-clocking op-
tions, allows the re-clocking of the di-
gital audio signal based on an external
WCLK or 10 MHz reference. In this case
the reference signal has to be supplied
at the BNC input. In any case, the digital
audio or Word Clock output signal con-
tains the same basic frequency as the
input signal. It is phase-locked but not
phase-synchronized to the external re-
ference clock source. In the functional
group ‘Clock In’, the clock rate of the di-
gital audio input signal is displayed and
the Word Clock outputs are multiplied by
using the clock multipliers in their rate.
Preamble
When the audio professional hears the
term ‘jitter’, he starts to jitter like the
just quoted spectre itself. In August and
September 2008, my colleague Frie-
demann Kootz had already commen-
ted in great detail on this topic, so I
should not go here into this subject in
full again. Who wants to read about all
the details again, finds both posts on
our website in the ‘Freizone’. Formula-
ted simply, jitter means an inaccuracy
of the clock, in other words, an unwan-
ted phase modulation of a pulse signal.
There not only exists one form of ‘jitter’
but several types of this phenomenon.
To eliminate them entirely, the develo-
pers go quite different ways. In any case
artifacts in the (converted) analog au-
dio signal can arise by a jitter afflicted
timing that, in contrast to the standard
analog world, really sounds not musi-
cal: intermodulation, non-harmonic dis-
tortion, lack of phase synchronization of
stereo signals which can significantly af-
fect the spaciousness or signal depth.
But also a blur of impulse, a weak loca-
lization or signal dissociation in a mix
can happen. The question of the worthi-
ness of an external clock over the inter-
nal has already been answered clearly
negative in some publications. In my ex-
perience it is more relevant whether the
circuit design of a converter and its chip
peripherals is likely to improve the si-
gnal quality by an external clock. Unpre-
dictable in a particular case, many fac-
tors are responsible for the expected
positive impact of an at most jitter-free
external clock signal. But you should al-
ways expect that even good converters
can benefit sound-wise from external
clock generators.
Hearing
I considered very long and hard whether
I could find a way of factual evidence
in the given time that does not culmi-
nate in the fact that you simply have
to believe me my listening experiences.
So far I have not discovered any me-
thod that could really endure this. So
it remains, at least for the moment, at
a hearing test, the results of which I
describe as concisely as possible. Of
course, there are methods of measure-
ment that eject the jitter as an ‘absolute
value’ but it is still not clear in this way
which sound effects in particular are as-
sociated with it. For my listening test I