About the Dolby Digital Professional Encoder Pane

This section contains detailed information about the various tabs within the Dolby Digital Professional (AC-3) Encoder pane of the Inspector window.

Figure. Dolby Digital Professional encoder pane in the Inspector window.

You make your Dolby Digital Professional settings using the tabs described below, by either modifying an existing setting or creating a new setting in the Settings tab. The Dolby Digital Professional pane opens with the default Audio tab on top. The Dolby Digital Professional pane contains the following items: basic settings, Audio tab settings, Bitstream tab settings, and Preprocessing tab settings.

Basic Settings

Use the following basic settings to set up a Dolby Digital Professional (AC-3) job or batch.

  • File Extension: This field displays the Dolby Digital Professional file extension (.ac3) automatically after the Dolby Digital Professional output format is selected from the File Format pop-up menu or the (+) pop-up menu in the Settings tab.
  • Allow Job Segmenting: This checkbox allows you to turn off job segmenting. Since job segmenting is not used for audio-only encodes, this checkbox is not active with the Dolby Digital Professional file format. For more information, see Job Segmenting and Two-Pass or Multi-Pass Encoding.
  • Audio, Bitstream, and Preprocessing: These buttons open the Audio, Bitstream, and Preprocessing tabs described next.

Audio Tab Settings

All the most important Dolby Digital Professional settings are accessible in the Audio Tab.

Figure. Audio tab of the Dolby Digital Professional encoder pane in the Inspector window.
  • Enable Low Frequency Effects: Select this checkbox to include the LFE channel in the encoded stream (not available for 1/0 mono or 2/0 stereo).
  • Dialog Normalization: Specifies the average volume of the dialogue, using decibels of full scale (dBFS), in your sound files relative to full modulation. The playback device uses this information to maintain similar volume among different AC-3 streams. The goal is to make all AC-3 encoded audio files have the same listening level, regardless of the source file.

    It is especially important to properly use the Dialog Normalization feature if you have different audio files (with different volume levels) going on to a DVD. If you know the average level for each file, enter that number in the Dialog Normalization field for each file. For example, if the dialogue in your Final Cut Pro sequence averages around –12 dB on the audio meter, enter –12 in the Dialog Normalization field.

    Note: This normalization is between the audio streams on the DVD, not within an individual audio stream itself. For that type of normalization, use an audio editing tool like Soundtrack Pro. You can enter values from –1 dBFS to –31 dBFS. The difference between the value you enter and 31 dBFS (which represents the normal dialogue listening level) is the amount that the source audio will be attenuated.

    • If you enter –31 dBFS: The attenuation is 0 dB (31 dBFS–31 dBFS), and the source audio levels are not affected at all.
    • If you enter –27 dBFS: The attenuation will be 4 dB (31 dBFS–27 dBFS).
    • If you enter –12 dBFS: The attenuation is 19 dB (31 dBFS–12 dBFS).

    The louder the source file, the smaller the value you enter, and the more the audio in the encoded file is attenuated during playback.

    If you do not know the sound level of the source file or for some other reason want to ensure the Dolby Digital Professional encoder does not affect your sound levels, enter –31 for the Dialog Normalization and choose None in the Compression Preset pop-up menu (located in the Preprocessing tab).

    Important: It is critical that you set Dialog Normalization correctly if you intend to use any of the 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.

Bitstream Tab Settings

These settings are stored in the finished stream for use by the playback device. Leave them at their default values unless you have a specific technical reason for changing them.

Figure. Bitstream tab of the Dolby Digital Professional encoder pane in the Inspector window.
  • Copyright Exists: Select this checkbox to specify that a copyright exists for this audio.
  • Content is Original: Select this checkbox to specify that this audio is from the original source and not a copy.
  • Audio Production Information: Select this checkbox and fill in the fields below to specify how the encoded audio content was mixed. Playback devices may use this information to adjust output settings.
    • Peak Mixing Level: Specifies peak sound pressure level (SPL) (between 80 dB and 111 dB) in the production environment when this mix was mastered.
    • Room Type: Specifies information about the mixing studio.

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.

Figure. Preprocessing tab of the Dolby Digital Professional encoder pane in the Inspector window.
Compression Preset
General
  • Apply Digital Deemphasis: Specifies whether input audio data is preemphasized and needs to be deemphasized before encoding.
LFE Channel
  • Apply 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 Channels
  • Apply 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.
  • Apply 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 offsets.
Surround Channels
  • Apply 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 Surround-compatible output.
  • Apply 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.