Dolby Digital settings in Compressor
The built-in Dolby Digital settings in Compressor (in the Create Blu-ray and Create DVD destinations, as well as in the built-in AC-3 and EC-3 audio settings) use the Dolby Digital transcoding format. This format encodes Dolby Digital (AC-3) and Dolby Digital Plus (EC-3) audio files that contain multiple audio channels, including 5.1 surround sound.
Note: You can also create custom settings that use the Dolby Digital transcoding format. However, the built-in Dolby Digital settings (in the Settings pane) analyze your source media and assign optimal properties to ensure the best possible transcoding results.
The properties of built-in and custom settings that use this transcoding format are located in the General inspector and Audio inspector (described below).
Displays the setting name and transcoding format, as well as an estimated output file size. When you add a setting to a job or change the setting’s properties, this summary is automatically updated.
Name: Displays the name of the setting.
Description: Displays the description of the setting.
Extension: Displays the extension of the output file (.ac3 or .ec3).
Allow job segmenting: This checkbox is dimmed because job segmenting is not available for settings that output only an audio file.
Default location: Choose an item from the pop-up menu to set the default save location for transcoded files.
File type: Choose a file type from the pop-up menu (Dolby Digital or Dolby Digital Plus, an enhanced version of the Dolby Digital audio compression technology).
Sets the processing algorithm used to adjust the frame rate during transcoding. Select one of the following options:
Set to percent of source using: Modifies the output clip’s speed by a percentage of the source clip’s speed. Enter a value in the percentage field or choose a preset value from the adjacent pop-up menu (with a down arrow).
Set to: Sets the duration of the clip. Enter a timecode duration in the field or click the arrows to increase or decrease the time.
So source frames play at [frame rate] fps: Nondestructively changes the playback speed of the clip without discarding frames or creating new frames. This property has no effect unless the “Frame rate” value in the Video inspector is different from the source file’s frame rate. For example, if you add a 10-second source file with a frame rate of 24 fps to Compressor, set the “Frame rate” property in the Video inspector to 25 fps, and then select “So source frames play at 25 fps” in the General inspector, the resulting duration of the transcoded clip (at 25 fps) will be 9 seconds and 15 frames.
For more information, see Retime video and audio using Compressor.
Channel layout: Use this pop-up menu to manually set the type of audio channel layout. For more information about audio channel layouts, including the surround sound channel layout, see Audio channel layouts in Compressor.
Sample rate: Use this pop-up menu to set the number of times per second that music waveforms (samples) are captured digitally. The higher the sample rate, the higher the audio quality and the larger the file size.
Note: All files intended for video and audio DVD authoring must have a 48 kHz sample rate as required by the DVD specification.
Target system: Use this pop-up menu to identify the system on which you are going to play the output file. Compressor limits options in other related properties to those appropriate for the target system.
DVD Video: Choose this option if you’re encoding for use in a DVD video authoring application.
DVD Audio: Choose this option if you’re encoding for use in a DVD audio authoring application.
Generic AC-3: Choose this option to remove the target system setting limit (the most generic choice).
Data rate: Use this pop-up menu to set the number of kilobits per second (kbps) required to deliver your audio file. Using a higher rate produces a higher-quality audio file.
Tip: For stereo encoding, rates of 192 kbps and 224 kbps are typical and will produce good results. For Dolby Digital 5.1 encoding, a rate of 384 kbps is recommended. For Dolby Digital Plus encoding, a rate of 192 kbps is recommended.
Bit stream mode: Use this pop-up menu to define the audio service contained within the Dolby Digital or Dolby Digital Plus bitstream.
Surround mode: When using a Mono or Stereo (L R) channel layout, this property tells the playback device whether the two-channel encoded bitstream contains a Dolby Surround (Lt/Rt) program that requires Dolby Pro Logic decoding. Choose an option from the pop-up menu:
Not Indicated: Does not send the playback device information about whether the bitstream was encoded in Dolby Surround.
Not Encoded: Tells the playback device that the bitstream contains information not encoded in Dolby Surround.
Surround Encoded: Tells the playback device that the bitstream contains information encoded in Dolby Surround.
Surround EX Mode: When using a 5.1 (L R C LFE Ls Rs), 5.0 (L R C Ls Rs), 4.1 (L R LFE Ls Rs), or 4.0 (L R Ls Rs) layout, this property tells the playback device whether the audio has been encoded in Dolby Digital Surround EX. Choose an option from the pop-up menu:
Not Indicated: Does not send the playback device information about whether the bitstream was encoded in Dolby Digital Surround EX.
Not Encoded: Tells the playback device that the bitstream was not encoded in Dolby Digital Surround EX.
Surround Encoded: Tells the playback device that the bitstream was encoded in Dolby Digital Surround EX.
Stereo downmix: Use this pop-up menu to set how to downmix a surround signal to a stereo signal. See Audio channel layouts in Compressor.
Important: The LFE signal may be discarded by the Dolby Digital downmix process.
Lo/Ro center, Lo/Ro surround, Lt/Rt center, Lt/Rt surround (for surround sound output): Use these pop-up menus to set the decibel level at which the surround and center channels are downmixed. Properties are enabled or disabled based on the channel layout you choose.
DRC line mode: Use this pop-up menu to set the dynamic range compression-processing mode. The default setting, Film Standard, is recommended for all use cases.
DRC RF mode: Use this pop-up menu to set the dynamic range compression-processing mode for RF devices (TV sets, cable set top boxes, or other devices that have RF connections).
LFE low-pass filter: Select this checkbox to apply a 120 Hz low-pass filter to the low-frequency effects (LFE) channel during output.
DC filter: Select this checkbox to apply a DC (direct current) high-pass filter to all input channels. Although this filter provides a simple way to remove DC offsets, note that most mixed audio material is already free of DC offsets.
Surround channels: 90 phase-shift: This checkbox, which applies a 90-degree phase shift to the surround channels, is selected by default. The shift in phase decorrelates the front and back channels and prevents the L and Ls signals from canceling each other out if a surround-compatible downmix is later applied to the decoded signal.
Surround channels: 3dB attenuation: Select this checkbox to apply a 3 dB cut to the surround channels during output. This option is intended for multichannel output (like a film soundtrack) that is 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.
Dialog normalization: Enter a value in the field to set the loudness of the program in your sound files relative to full modulation. The playback device uses this information to maintain similar loudness among different AC-3 streams. The goal is to give all AC-3–encoded audio files the same listening level, regardless of the source file.
For a list of available audio effects and instructions on how to add an audio effect to a setting, see Add and remove effects in Compressor.
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