Audio properties of presets in Compressor
The audio properties of a preset can be found in the Audio inspector (when the preset is selected).
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 unmodified to the destination file. When this checkbox is selected, all the other presets in the Audio Properties area are disabled. | |||||||||
Channel layout | All audio-enabled preset formats | 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 | All audio-enabled preset formats | 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. For MXF presets, this value is locked at 48 kHz. Note: All files intended for video and audio DVD authoring must have a 48 kHz sample rate as required by the DVD specification. | |||||||||
Sample size | All audio-enabled preset formats | Use this pop-up menu to manually set the sample size of the audio signal. For Apple Devices presets, this is always set to Automatic. | |||||||||
Codec | QuickTime Movie | Use this pop-up menu to choose an audio codec. | |||||||||
Sample format | QuickTime Movie | If you have selected Linear PCM as an audio codec, use this pop-up menu to select whether to output your audio in Big Endian or Little Endian format. | |||||||||
Format | MPEG-4 | If you have selected FLAC, MPEG-4 AAC, MPEG-4 HE AAC, MPEG-4 HE AAC V2, or Opus as an audio codec, use this pop-up menu to select the quality of the audio output. | |||||||||
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 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.
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Bit rate | Apple Devices, Dolby Digital, MP3, MPEG-4, QuickTime Movie | 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. 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 vary the number of bits used to store the music depending on the complexity of the music. 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 strategy used to encode the audio. There are four options:
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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 only 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 | Use this pop-up menu to manually set the amount of compression the FLAC encoder uses to encode the audio signal. This preset is only available for FLAC file types. | |||||||||
Joint stereo | MP3 | Select the checkbox to have one channel carry the 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. There are two options:
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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 | 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:
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Surround EX mode | Dolby Digital | 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:
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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. Properties are enabled or disabled based on the channel layout you choose. | |||||||||
DRC line mode | Dolby Digital | Use this pop-up menu to set the dynamic range compression-processing mode. The default preset, Film Standard, is recommended for all use cases. | |||||||||
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 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 | 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 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 | 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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