Audio properties of presets in Compressor
When you select a preset, its audio properties appear in the Audio inspector.
Important: Not all properties or options are available for all transcoding jobs. The options shown depend on the type of source media you’re transcoding, the preset’s format, the configuration of other properties, and the hardware and software you’re using.
Audio property | Preset formats | Description | |||||||||
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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:
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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:
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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:
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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. 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) | 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. | |||||||||
The Audio inspector also shows options for adding audio effects.
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