Date printed: 24.01.12
36
D21m System
no external sync signal if not necessary, and the output will be clocked with
the internal system clock. As soon as an external sync signal is provided to
the
AES EXT SYNC IN
connector, the output will automatically be clocked
by the extermal sync signal.
S7, S8 (Output Word Length)
(A949.0456 only)
Used for setting the resolution (output word length) for
the AES/EBU output channels (i.e. audio channel pairs 1+2, 3+4, etc.). Cor-
responding switches on S7 and S8 are used in pairs for each AES/EBU chan-
nel, according to the following table and the silkscreen on the PCB. Default
setting: All OFF, corresponding to 24 bit.
S7.x
S8.x
Output Word Length
OFF
OFF
24 bit
OFF
ON
20 bit
ON
OFF
18 bit
ON
ON
16 bit
Note:
For word length reduction the output SRCs must be set to enabled’; if so, the
output word length is always 21 bit maximum. Whenever an SRC is enabled,
the three least significant bits (LSB) are set to digital zero. This results in the
specified dynamic range of 120 dB.
Special Channel Status and User Bits Data Management
Some intercom systems use a standard AES stream to link control panels to
the main base station. In addition to the audio, control data is encoded into
the user bits of the AES stream. In order to allow an intercom remote control
panel to be transmitted from a Studer stagebox to the base station, a special
mode is available on these AES cards.
The channel status and users bits (CU bits) are extracted at the receiver side.
Depending on the setting of DIP switch S1, the CU bits are either embed-
ded into the two bottom LSBs of the audio (S1 = ON) or sent to the D21m
backplane (S1 = OFF). In addition, the channel status data block start (Z bit)
is also embedded into the bottom LSB of the audio to allow recovery of the
block start at the destination AES transmitter. If the ZCU bits are embedded
into the audio, the audio word length is reduced to 20 bits.
Note:
The resulting audio data contains non-audio information in the four bottom
bits of the 24 bit audio word and thus is no longer fully PCM. This non-PCM
signal may be routed through Studer routers and the routing part of all Studer
audio mixing systems, but will not pass through any active processing such
as a channel path or sample rate converter.
At the output side, an additional DIP switch (S2) allows the selection of the
source of the transmitted ZCU bits. Either a default, static pattern (S2 = OFF)
or the ZCU bits available from the backplane are encoded (S2 = ON). If S2
is ON then the bits from the position specified with S1 are encoded.
The following diagram illustrates the various DIP switches and their effect
upon the data path.
