Audio properties of presets in Compressor

Enable audio pass-through

QuickTime Movie

Select this checkbox to copy the source audio to the destination file, without modification.

Channel layout

All audio-enabled preset formats

Use this pop-up menu to manually set the type of audio channel layout. See Audio channel layouts in Compressor.

Sample rate

All audio-enabled preset formats

Use this pop-up menu to set the sample rate of the transcoded audio.

Sample size

All audio-enabled preset formats

Use this pop-up menu to manually set the sample size of the audio signal.

Codec

QuickTime Movie

Use this pop-up menu to choose an audio codec.

Sample format

QuickTime Movie

When the audio Codec property is set to Linear PCM, use this pop-up menu to select whether to output your audio in Big Endian or Little Endian format.

Format

MPEG-4

Use this pop-up menu to choose an MPEG-4 Advanced Audio Coding (AAC) or Apple Lossless format for MPEG-4 audio encoding.

Quality

Apple Devices, MPEG-4, QuickTime Movie

Use this pop-up menu to select the quality of the audio output.

Target system

Dolby Digital

Use this pop-up menu to choose the system on which you’ll play the output file. Compressor limits options in other related properties to those appropriate for the target system.

Bit rate

Apple Devices, Dolby Digital, MP3, MPEG-4, QuickTime Movie

Use this pop-up menu to set the bit rate of the audio output.

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.

Use variable bit rate encoding

MP3

Select the checkbox to have Compressor encode the file using a dynamic bit rate that varies according to the complexity of audio. Variable bit rate encoding can reduce the size of the output file.

Bit rate strategy

Apple Devices, MPEG-4, QuickTime Movie

Use this pop-up menu to select the method used to encode the audio:

• Constant Bit Rate: Uses the value set in “Bit rate” to determine the bit rate for the encoded audio.

• Average Bit Rate: Uses the value set in “Bit rate” to determine the target average bit rate for the encoded audio. This option provides a more consistent bit rate than variable bit rate.

• Variable Bit Rate Constrained: Uses the value set in “Bit rate” to determine the maximum bit rate for the encoded audio.

• Variable Bit Rate: Encodes the audio using a variable bit rate determined by Compressor. Choosing this option disables the “Bit rate” menu.

Include Dolby 5.1 Audio Track

Apple Devices

Select the checkbox to add surround sound as a Dolby Digital audio track for playback on Apple TV.

Include Lt Rt downmix track

QuickTime Movie

Select this checkbox (available when “Channel layout” is set to more than two tracks) to add an additional stereo track to the transcoded file that includes a stereo-mix version of the audio with the encoded surround information included.

Compression

Common Audio Formats

For FLAC file types, use this pop-up menu to manually set the amount of compression used to encode the audio signal.

Joint stereo

MP3

Select the checkbox to have one channel carry information that’s identical on both channels, and another channel carry unique information. At bit rates of 160 kbps and below, this preset can improve the sound quality of your converted audio.

Smart encoding adjustments

MP3

Select the checkbox to have Compressor analyze the source file and the preset’s encoding properties to maximize the quality of the output file.

Filter frequencies below 10 Hz

MP3

Select the checkbox to have Compressor remove inaudible frequencies from the source file and output a smaller and more efficient file without perceptible loss of quality.

Channels as

MXF

Use this pop-up menu to set the distribution of audio channels. "Mono tracks” uses a separate track for each audio channel, while “Multitrack” combines all audio channels into a single track.

Bit stream mode

Dolby Digital

Use this pop-up menu to define the audio service contained within the Dolby Digital or Dolby Digital Plus bitstream.

Surround mode

Dolby Digital

For Mono and Stereo (L R) channel layouts, 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

Dolby Digital

For 5.1 (L R C LFE Ls Rs), 5.0 (L R C Ls Rs), 4.1 (L R LFE Ls Rs), and 4.0 (L R Ls Rs) layouts, 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 Surround EX.

• Not Encoded: Tells the playback device that the bitstream contains information not encoded in Dolby Surround EX.

• Surround Encoded: Tells the playback device that the bitstream contains information encoded in Dolby Surround EX.

Stereo downmix

Dolby Digital

Use this pop-up menu to set how to downmix a surround signal to a stereo signal. See Audio channel layouts in Compressor.

Lo/Ro center, Lo/Ro surround, Lt/Rt center, Lt/Rt surround (for surround sound output)

Dolby Digital

Use these pop-up menus to set the decibel level at which the surround and center channels are downmixed.

DRC line mode

Dolby Digital

Use this pop-up menu to set the dynamic range compression-processing mode.

DRC RF mode

Dolby Digital

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

Dolby Digital

Select this checkbox to apply a 120 Hz low-pass filter to the low-frequency effects (LFE) channel during output.

DC filter

Dolby Digital

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

Dolby Digital

This checkbox, which applies a 90-degree phase shift to the surround channels, is selected by default. The shift in phase unlinks 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

Dolby Digital

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’s 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

Dolby Digital

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.