MRD 3187B - User Manual
Page 239 (245)
Appendix F – MRD 3187B Audio Explanation
Audio Setup
There are three primary modes of audio down mix operation for the
8730A/8731A/8732/8734 decoders. These settings only affect the signal if the digital
output is set to “PCM.” It will also affect those embedded audio channels that are set
to a PCM down mix.
The modes are “Monitor” (the default setting), “Transmission”, and “User.”
Note: There are no gain changes if the digital or embedded outputs are set to
Raw.
The first mode is “Transmission.” It allows no changes by the customer. It is intended
to provide a limited dynamic range signal to drive a set top box or a transmitter. The
“Transmission” mode does respond to dialog normalization data. It provides a gain
boost of 11 dB and has compression to prevent the signal from overdriving a
modulator. The 11 dB gain boost is applied to the analog outputs, AES digital outputs
set to PCM, and any embedded outputs set to PCM.
Note: It will not affect the gain of digital outputs or embedded outputs set to Raw.
It is intended to provide a similar audio level as a broadcast TV station signal through
an RF modulator. The down mix includes the “center” and “surround” channels if they
are present, and is represented as Lt/Rt. (left total/right total)
The second mode is “Monitor.” It has moderate processing, no gain boost and its
down mix involves left and right channels only (L/R). The compression setting is
“Line” mode as the default, but may be changed to “RF”, “Custom 0” or “Custom 1.” In
“Line” mode, the Dolby dialog normalization data is followed. No other parameters
may be set by the customer. It is intended for monitoring of sources with only some
peak limiting protection. Selecting “RF” as the compression setting will add 11 dB of
gain and the same processing as the “Transmission” mode to the analog outputs,
AES digital outputs set to PCM, and any embedded outputs set to PCM. The down
mix is L/R (left only/right only)
The third mode available is “User.” It allows all parameters to be set by the operator.
The compression choices are “RF”, “Line Mode”, “Custom 0”, and “Custom 1.” RF
and “Line Mode” essentially duplicate the first two modes of audio mix down
described above. The “Custom 0” and “Custom 1” modes have no audio processing
or gain boost. “Custom 1” does enable gain changes called for by the dialog
normalization data. It allows the operator to enable or disable the dynamic range
(peak limiting) and select the channels to downmix “Lt/Rt”, “L/R”, “Auto”, “Mono L”,
and “Mono R”. Mono left or Mono right applies that signal to both left and right
channels of the digital service, left and right channels of the analog outputs, and left
and right channels of any embedded stream set to PCM. “Auto” was introduced with
Dolby Digital Plus and will select the downmix of Lt/Rt or L/R based on the received
audio metadata. If the metadata is not present or Dolby Digital audio is received, Lt/Rt
down mixing is used.
“Custom 0” disregards the Dolby dialog normalization data and runs at a fixed gain.
Choosing “RF” as the compression mode will increase the gain by 11 dB for the
analog outputs, AES digital outputs set to PCM, and any embedded outputs set to
PCM.
If you want to run with no processing, set “User / Custom 1 / L/R / Dynamic Range” to
disabled. This will still allow gain changes called for in the Dolby metadata.
Audio Output Settings
The digital audio services may be set to “PCM” (AES) or “Raw” as an output. This
applies to all available sources. The “PCM” setting will pass an AES stream, or
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