Preprocessing Tab Settings
Preprocessing options are applied to the audio data before encoding. With the exception
of the Compression Preset setting, leave these settings at their default values unless you
have a specific technical reason for changing them.
• Compression Preset: Specifies one of the dynamic range processing modes built in to
the AC-3 format. The default of Film Standard Compression should only be used when
you are encoding an original mix intended for cinema. In almost all cases, you should
It is critical that you set the Audio tab’s Dialog Normalization correctly if
you intend to use any of these Compression Preset settings. The Compression Preset
settings assume that the audio, after the dialogue has been normalized, is at the normal
listening level of 31 dBFS. Levels that are consistently louder than that result in distorted
sound and erratic levels.
Note: If you are building a Dolby Digital Professional 5.1-channel surround sound DVD,
you will use Film Standard Compression.
• Digital Deemphasis: Specifies whether input audio data is preemphasized and needs
to be deemphasized before encoding.
Creating Dolby Digital Professional Output Files
• Low-Pass Filter: Select this checkbox to apply a 120 Hz low-pass filter to the Low
Frequency Effects (LFE) channel. Turn off this filter if the digital signal fed to the LFE’s
input does not contain information above 120 Hz.
Full Bandwidth Chan.
• Low-Pass Filter: Select this checkbox to turn on a low-pass filter with a cutoff near the
available audio bandwidth that is applied to the main input channels. If the digital
signal fed to the main input channels does not contain information above the available
audio bandwidth, you can turn off this filter. Compressor will automatically determine
the available bandwidth.
• DC Filter: Select this checkbox to turn on a DC high-pass filter for all input channels as
a simple way to remove DC offsets. Most mixed audio material is already free of DC
• 90º Phase Shift: Select this checkbox to generate multichannel AC-3 streams that can
be downmixed in an external two–channel decoder to create true Dolby
• 3 dB Attenuation: Select this checkbox to apply a 3 dB cut to the surround channels of
a multichannel film soundtrack being transferred to a consumer home theater format.
Cinema surround channels are mixed 3 dB “hot” (higher) relative to the front channels
to account for cinema amplifier gains.