Sonnox Fraunhofer Pro-Codec - Manual (Page 23)

5.4 BitstreamLevel(TRIM Tab) 5 THE PRO-CODEC PLUG-IN
5.4 BitstreamLevel(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
are not exactly repeatable from one cycle to the next. Furthermore, in some host
applications, repeatedly rewinding to the beginning of the track will also result in
www.sonnox.com 23 Gotocontents