Additional Information - Neumann.Berlin DMI-8 Bedienungsanleitung

7.

Additional information

7.1 AES42
This standard is based upon the use of a 2-line
balanced cable (AES/EBU cable; for short con-
nections conventional analog cable can also be
used). The power supply for digital microphones
is defined as Digital Phantom Power (DPP) with
+10 V and max. 250 mA. Modulation of the phan-
tom voltage generates a remote control data
stream which is transmitted to the microphone
(+2 V pulses).
The data format of the digital audio signal trans-
mitted from the microphone complies with the
AES/EBU (AES3) standard. The user bits defined
in this standard are intended for the transmission
of various types of information. The AES42 stan-
dard defines the significance of these user bits
with regard to digital microphones. In the DMI-
8, these data are separated from the audio sig-
nal and are transferred to the control bus, which
serves as an interface for a computer or control
device.
Fig. 3 shows a simple functional diagram of a mi-
crophone interface with an AES42 input and an
AES/EBU output.
7.2 XLR cables
The length of cable that can be used from a
digital Neumann microphone to the DMI-8 is
dependent upon the type of cable and upon the
sampling rate (word clock frequency) selected.
For cable lengths of up to 100 m with a sampling
rate of 44.1 kHz or 48 kHz, high-quality "analog"
XLR 3 cable (e.g. the Neumann IC 3 cable) can be
used. For greater cable lengths, the use of AES/
EBU cables (110 ohms) is required. If AES/EBU
cables are used, the following cable lengths are
typical: Up to 300 m for sampling rates of 44.1
kHz or 48 kHz; up to 200 m for sampling rates of
88.2 kHz or 96 kHz; and up to 100 m for sampling
rates of 176.4 kHz or 192 kHz.
Attention: If a long cable is used to connect the
microphone and the DMI-8, the DC resistance of
the cable used must not exceed a specified maxi-
mum value, since excessive DC resistance would
result in an impermissible voltage drop in the
phantom power. The following formula applies:
Rc/2 + Rs < 18 ohms
Rc = DC resistance of the individual cable core,
Rs = DC resistance of the shield or the GND re-
turn line.
The length of cable that can be used from the
DMI-8 to subsequent equipment (e.g. a digital
mixing console) is substantially dependent upon
the technical features of the subsequent equip-
ment. Thus no specific statements can be made
concerning the cable length. In case of doubt,
the use of AES/EBU cables (110 ohms) is recom-
mended.
7.3 Operation without the RCS control software
All of the settings which are in effect when the
DMI-8 is switched off are stored internally, and
are automatically sent to the microphone when
the equipment is switched on again. The most
recent microphone settings are restored, without
requiring a connection to the control device (PC
or Mac).
The same procedure is followed if a microphone is
connected to the DMI-8 later, after the DMI-8 has
already been switched on.
When the RCS control software is started, the con-
figurations stored there for all of the microphone
channels are compared with the settings stored in
the DMI-8. If differences are detected, a menu is
displayed that asks which configuration is to be
used (see the RCS Operating Manual).
7.4 Synchronization
The AES42 standard describes the following two
modes for synchronizing the microphone with the
receiver (e.g. a mixing console or the DMI-8 Digi-
tal Microphone Interface).
Mode 1: The microphone operates asynchronous-
ly, using the sampling rate of its internal quartz
oscillator. In this case, a sample rate converter is
required at the receiver. It should be noted that
sample rate converters can impair the signal qual-
ity in terms of dynamic range and enlarge the la-
tency time.
Attention: This mode is not supported by the
DMI-8
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