|Tutorial: -Why does my DVD audio level differ from the level in FCP?
my DVD audio level differ from the level in FCP?
by Jon Chappell
Have you noticed a discrepancy between the audio
in your Final Cut Pro timeline and the audio of the finished
DVD when using Compressor's DVD presets?
That's because the Dolby Digital 2.0
audio preset in Compressor has several functions to improve unsuitable
audio, but if you have already mixed your audio they might do
more harm than good in some cases. Rather than just telling you
which settings to use, I'm first going to explain what these
functions are designed to do because there are a lot of misconceptions
Compression alters your dynamic range
(the difference between the loudest and quietest sounds in a
soundtrack) by compressing the level of sounds to fit within
a certain range. The loudest sound in a Dolby soundtrack can
be 105dB. Considering the fact that prolonged exposure to 90
dB audio can result in hearing loss, most people do not play
their audio at 105dB. When you set up a Dolby decoder with a
reference tone, you are telling it the volume level it should
play 105dB audio at. So if this is lower than 105dB (which is
likely), you will lose some of the very quiet sounds on the soundtrack.
The compression presets allow you to regain these sounds by sacrificing
some dynamic range in the process.
It is set to Film Standard by default
but if you have already performed a mix with a moderate dynamic
range, further compression is not likely to be necessary and
so it is worthwhile to switch this to None.
Dialog normalization is a feature on
several Dolby decoders that ensures all content plays back at
the same level. The listener sets their preferred playback level
and the dialogue in every DVD and TV show plays back at the same
level, meaning you don't need to keep reaching for the remote
in order to adjust the volume. Contrary to popular belief, it
only adjusts the overall volume level when the source
changes (i.e. when you begin playing the DVD or when a new TV
program begins) so dynamic range is preserved throughout the
movie. It does not dynamically adjust the volume as the movie
The normalization value indicates the
difference between the overall level of dialog and the maximum
audio peak of 0 dBFS. The default is set to -27 dBFS, which is
the established level for film soundtracks. It is also the level
most decoders are set to by default. If you have your decoder
set to -27 dBFS and then, for example, try to play a -25 dBFS
movie, the decoder will lower the overall volume by 2 dBFS so
that the general dialogue level remains the same. If you do want
to switch it off when compressing your audio files (if you've
already leveled your sound mix for example), set it to -31 dbFS.
So if you would like your audio to be
exactly how it was in Final Cut Pro, set Dialog Normalization
to -31 dBFS and set Compression in the Pre-Processing
tab to None. However, these functions do serve useful
purposes for the end user and it is worthwhile to bear their
needs in mind.
Copyright 2009 Digital Rebellion,
This article was first published
on Digital Rebellion
and is reprinted here with permission from the author.
Jon Chappell is an editor, VFX artist
and software developer originally from the UK. He is the owner
of Digital Rebellion
LLC and is a regular contributor to the Final Cut Pro community.
He is well known for developing the popular troubleshooting applications
Manager and Compressor
Repair. His film credits include the award-winning feature