User guide
821189: AMP1-16-M User Guide
© 2014 Wohler Technologies, I n c . A l l r ights reserve d .
33
Ch apter 4 Internal Menu System
Op ti o ns M enu
timeout period elapses without any front panel control activity, the
screens will dim further. Operating any button or control will
instantly brighten the screens.
•
Audio Muting & Delay
: Pressing this button selects the
Non-
Audio
,
PA Header
, and
Delay
adjustment. Rotating the
Trim
knob changes the selected adjustment within its range. The
Non-
Audio
and
PA Header
detection can be either enabled or disabled.
These controls determine if and how much to mute non-audio
signals, such as Dolby bitstreams. The
Delay
can be either
Off
or 4
to 160 ms. The default settings are:
•
Non-Audio
: Enabled
•
PA Header
: Disabled
•
Delay
: 4 ms
The AMP1-16-M can detect whether a digital audio stream
contains PCM encoding, or some other compressed data format
such as Dolby Digital™ , in two different ways.
The bitstream contains a non-audio bit. When set, this indicates
that the bitstream is not PCM encoded, and therefore, should be
muted. This bit occurs once every 4 ms in a 48 kHz audio stream.
Unfortunately, some equipment does not set this bit even when a
bitstream is not PCM encoded, or will erroneously set this bit
when a bitstream is PCM encoded. Thus, there is also a second
method of detection.
This unit can look for special words within the data stream known
as PA Headers. These headers occur once every video frame.
Assuming the slowest frame rate of 24 FPS, these occur every 42
ms. Thus, the delay should be set to a minimum of 42 ms for this
detection method alone. The inherent problem with this detection
method is that if the bitstream is altered in any way (gain change,
equalization, or other forms of processing) these words will also be
scrambled and not detected. However, if the non-audio bit is set
correctly, it will survive these processes.
You may choose to employ neither, either, or both detection
methods. If the amount of delay entered is too short, there may be
a small burst of noise when an incoming audio stream switches
from PCM encoding to a compressed format.
•
Select
: Pressing this button and then rotating the
Trim
knob
selects the phase indicator to be adjusted. Press the
Select
button to