Pro-Codec User Manual

5.4 Bitstream Level (TRIM Tab) 5 THE PRO-CODEC PLUG-IN
5.4 Bitstream Level (TRIM Tab)
Any form of filtering can, under certain circumstances, increase the peak level of the
signal. Therefore, if your input is hot, the encoding process can produce overloads that
are not seen until the signal is decoded. This effect can be very easily demonstrated with
the Pro-Codec Plug-In.
The Bitstream
Level TRIM tab can be used to monitor this
potential for overload. The post-decoder level
of each selected codec is continually monitored,
and a small meter indicates levels greater
than 0 dBFS. There is a peak-hold text display
(MAX dB) to show the maximum post-decoder
level achieved. This text is white if below
0 dBFS and turns red on overload. Clicking on
this display resets the overload condition.
The TRIM dB control allows you to trim the input
level to the codec to prevent these overloads. The gain reduction is applied
pre-encoding, and if non-zero the trim value is displayed darker. In order to allow equal
loudness listening comparison and difference signal generation, the trim is applied before
encoding and inversely applied after the decoder output. This way the encoded bitstream
is reduced in level, but the auditioned signal remains at the same level as the input
signal.
The TRIM dB controls can be automated for use with online encoding. For convenient
trimming, the value in the MAX dB window can be dragged and dropped onto the TRIM
dB cell. The MAX dB value can be repeatedly dropped onto the TRIM cell; each time the
value is subtracted from the current TRIM value. In the screenshot above, codec 1 is
overloading by 0.73 dB. Selecting and dragging the value from MAX dB to TRIM dB will
set the latter to -0.73 dB.
This post-decoder level overload monitoring is present even if the TRIM tab is deselected
via permanently visible overload LEDs to the right of each of the five codec selection
slots. Clicking on an overload LED resets the overload condition for that codec.
It is important to note that the indicated Bitstream metering and overload LEDs are
provided as a guide only. If a segment of audio is being cycled, these maximum values
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