821016: AMPx-E8 Series User Guide
© 2011 Wohler Technologies, Inc. All rights reserved.
66
Chapter 6
Setup Menu
Bitstream Detection
Step through settings using the
Up
or
Down
buttons, select -9dB (for
example). To accept, press the
Enter
button. To exit without saving,
press the
Esc
button.
Bitstream Detection
The unit will now mute an input pair if it detects the presence of a non-
PCM stream (such as a Dolby or DTS bitstream) on that pair. The unit
detects bitstreams with two methods:
A.
Preamble detection
B.
Not-Audio AES Channel status flag is asserted
In terms of Method A, encoded bitstreams contain key data sequences
that identify the type of encoding used. These sequences are known as
preambles (see the SMPTE 337 and 338 standards). This unit can only
detect 16-bit preambles. For example, a 20-bit Dolby E stream would be
passed as PCM audio, instead of being flagged as an encoded stream.
This method is always employed.
In terms of Method B, the upstream equipment must either assert or
de-assert this flag. Unfortunately, not all equipment does this correctly.
In those cases where the channel status flag is set incorrectly, you may
need to disable this method of bitstream detection. This can be done
using the setup menu item
A Vld Det
. When enabled (
Ena
), Method B
is used to detect bitstreams. When disabled (
Disa
), Method B is not
used to detect bitstreams. If your unit is muting PCM streams, set this
item to
Disa
. If encoded bitstreams are getting through to the speakers,
set this item to
Ena
.
Important:
Surround gain adjustments are only effective for downmixes DM1 and
DM2. In downmix DM3 the surround gain is fixed.