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Netflix Sound Mix Specifications & Best Practices v1.1

1.0 Nearfield Audio Prerequisites for Mix Facilities
1.1 Nearfield 5.1 Surround Mix - Original Version, Dub Mix, Audio Description
1.2 Nearfield 2.0 Stereo Mix - Original Version, Dub Mix, Audio Description
1.3 Nearfield 5.1 Surround M&E Mix
1.4 Nearfield 2.0 Stereo M&E Mix
1.5 Nearfield Atmos Mix
1.5.1 For Distribution
1.5.2 For Localization
1.5.3 For Archive
2.0 Theatrical Mix - Mastering and Archive
3.0 Best Practices
3.1 Dialog-Gated Loudness and Loudness Range
3.2 Peaks
3.3 Room Setup


1.0 Nearfield Audio Prerequisites for Mix Facilities

Average loudness must be -27 LKFS +/- 2 LU dialog-gated. Peaks must not exceed -2db True Peak. Audio should be measured over full program according to ITU-R BS.1770-1 guidelines.

Standard or RF64 discreet LPCM .wav or .bwav files are required, with two exceptions:

  1. Where multi-channel (interleaved) files are inherent to the source, such as with IMF, Quicktime or Atmos BWAV ADM delivery.
  2. Localized Mix (Dub mix) .wavs delivered to Backlot may be .mov-wrapped

Content Hub deliveries may be discreet audio files alone, within folders or within Pro Tools session folders also containing sessions. Where project files other than Pro Tools are delivered, AAFs/OMFs should also be included, or all channels must be rendered to continuous PCM audio.

Lossy or lossless audio compression is never allowed. Audio must be linear PCM.

Sample Rate and Bit Depth:

  • 48k/24bit for Original Language Mix or M&E Mix. Applies to Stems & Mix Masters.
  • 48k/16bit or 24bit for Secondary Language or Audio Description.

Audio must be recorded in sync to picture at native project frame rate. All audio deliverables should match the camera and picture post production frame rate. All audio must sync to final IMF/Prores picture delivery.

If conformed 5.1 audio was never created, stereo audio will be accepted (mono audio is acceptable if the program's original source is mono and no stereo and/or 5.1 mix exists. Mono audio must be duplicated on channels 1 & 2 and delivered as 2-channel).

1.1 Nearfield 5.1 Surround Mix - Original Version, Dub Mix, Audio Description

  • Use 79db spl or 82db spl as your standard reference level for mixing
    Meet a -27 LKFS (+/- 2 LKFS) average dialog-gated level using ITU-R BS.1770-1 measured over entire program
    Maintain +18db (-2 dbfs) maximum level (true peak) over reference of -20 dbfs, achieved by peak limiting and not lowering the mix level
    Provide 5.1 Dialog, Music and Effects stems that equal the 5.1 mix when combined

1.2 Nearfield 2.0 Stereo Mix - Original Version, Dub Mix, Audio Description

  • Use 79db spl or 82db spl as your standard reference level for mixing
  • Provide a separate Lo/Ro or LT/RT mix with -27 LKFS (+/- 2 LKFS) dialog-gated using ITU-R BS.1770-1 measured over entire program
    • Lo/Ro mix is preferred
  • Lo/Ro or LT/RT mix to be mono compatible
  • Maintain +18db (-2 dbfs) maximum level (true peak) over reference of -20 dbfs, achieved by peak limiting and not lowering the mix level
  • When down-mixing from 5.1 to create Lo/Ro or LT/RT 2.0 mix:
    • Fold Low Frequency Effects (LFE) into both the LEFT and RIGHT CHANNELS
    • Low Pass Filter LFE at 200Hz or lower
    • Lower Center channel content by -3db
    • Center channel content should be included in both the LEFT and RIGHT CHANNELS
    • Lower Surround channel content by a minimum of -3db
    • Fold Left and Right Surround content into the corresponding LEFT and RIGHT CHANNELS
    • Optionally include the Low Frequency Effects (LFE) channel at -12db
  • All adjustments must be made to the individual 5.1 channels prior to folding down

Note: The resulting 2.0 mix must be checked prior to delivery to ensure it is free of any audio artifacts and if necessary, as determined by Netflix, further adjustments shall be made to prevent them.

1.3 Nearfield 5.1 Surround M&E Mix

  • 48kHz/24-bit
  • Provide a separate fully filled 5.1 surround mix containing only Music & Effects (no dialog)
  • Ambiences and foley fill should be included to correctly match original mix. Any non-dialog sound present in the main mix must also be represented in M&E mix.
  • All levels should mirror 5.1 mix used for final Mastering and Archive so that any newly added dubbed dialog can be mixed in easily later. Peaks must not exceed -2db True Peak.
  • M&E Options stem(s) as separate 5.1 WAV files
  • For mixers creating the M&E please reference the M&E Creation Guidelines.

1.4 Nearfield 2.0 Stereo M&E Mix

  • 48kHz/24-bit
  • Provide a separate fully filled 2.0 stereo mix containing only Music & Effects (no dialog)
  • Ambiences and foley fill should be included to correctly match original mix. Any non-dialog sound present in the main mix must also be represented in M&E mix.
  • Center channel content must be reduced 3db as a default setting for LoRo down mix
  • All levels should mirror 5.1 mix used for final Mastering and Archive so that any newly added dubbed dialog can be mixed in easily later. Peaks must not exceed -2db True Peak.
  • For mixers creating the M&E please reference the M&E Creation Guidelines.

1.5 Nearfield Atmos Mix

The Dolby Atmos Home Mix must meet the following requirements.

  • At a minimum, must be mixed in a 7.1.4 room
  • Dolby Certification is not required for Home Atmos mix rooms
  • This is a nearfield mix. The most common monitoring levels for nearfield are 79db or 82db.
  • Must conform to Netflix loudness spec (-27db LKFS +/- 2 LU 1770-1 dialog-gated).
  • Peaks should not exceed -2dbfs True Peak. To achieve this, we recommend setting True Peak limiters on all beds and objects at -2.3 or lower. Loudness and peaks should be measured via a 5.1 rerender.
  • For native Atmos mixes, the 5.1 and 2.0 rerenders must conform to Netflix loudness and Peak specification.
  • All beds and objects are encoded and will always be audible. A printmaster may utilize a composite of all bed material OR multiple beds, but not both.
  • For all series/doc/unscripted/comedy content, beds and objects must be separated by Dialog, Music and Effects. For film content, DME separation should be maintained whenever possible.
  • If a 85 db reference theatrical mix is created, two complete sets of deliverables are required. One for theatrical, one for nearfield.
  • Atmos files shall match final IMF picture length exactly as long-play and not separate reels. Leader and sync pop shall be removed.
  • FFOA must be left at default - leave “Add FFOA” box unchecked. For pre-3.0 renderer software, leave red dashes in FFOA value.

1.5.1 For Distribution

  • Final Home Theater Print Master
    • Single or multiple LCR, 5.0, 5.1, 7.1 or 7.1.2 bed(s)
    • Tracks 11-128 may be used for Objects or beds
    • 48 kHz, 24 bit
    • Dolby Atmos BWAV ADM File
  • Mix Minus Narration (when applicable)
    • Single or multiple LCR, 5.0, 5.1, 7.1 or 7.1.2 bed(s)
    • Tracks 11-128 may be used for Objects or beds
    • 48 kHz, 24 bit
    • Dolby Atmos BWAV ADM File

1.5.2 For Localization

  • Music & Effects mix
    • Dolby Atmos BWAV ADM or Pro Tools Recorder session
      • Single or multiple LCR, 5.0, 5.1, 7.1 or 7.1.2 bed(s)
      • Tracks 11-128 may be used for Objects or beds
      • M&E Options stems as separate WAV file(s)
      • Channel mapping must match the bed(s) of the M&E mix
      • 48 kHz, 24 bit

1.5.3 For Archive

  • All deliverables should be conformed and synced to the final picture as long-play
  • Final Home Theater Printmaster DAMF (Dolby Atmos Master File)
    • Components of DAMF are:
      • .atmos file
      • .audio file
      • .metadata file
    • Tracks should be grouped / associated to Dialogue, Music and Effects stems
    • Single or multiple LCR, 5.0, 5.1, 7.1 or 7.1.2 bed(s)
  • Mix Minus Narration DAMF (Dolby Atmos Master File) (when applicable)
    • Components of DAMF are:
      • .atmos file
      • .audio file
      • .metadata file
    • Tracks should be grouped / associated to Dialogue, Music and Effects stems
    • Single or multiple LCR, 5.0, 5.1, 7.1 or 7.1.2 bed(s)
  • Pro Tools Atmos full mix session (if requested)
  • Theatrical Dolby Atmos MXF used for DCP

2.0 Theatrical Mix - Mastering and Archive

  • Theatrical Mixes should follow the Near Field specification, listed above, with the following exceptions:
    • Use 85db spl as your standard reference level for mixing.
    • Theatrical mixes have no LKFS loudness requirement and may peak at 0db True Peak.
    • Provide Dialog, Music and Effects Stems at Theatrical spec

3.0 Best Practices

Note: The below are not Technical Specifications. The below is guidance to help achieve an optimal customer experience. Following the guidelines below is not required by Netflix, but is preferred.

3.1 Dialog-Gated Loudness and Loudness Range

Netflix is committed to protecting creative intent - we do not compress, limit or modify audio mixes. However, content which is not excessively dynamic provides a better experience for our customers.

We normalize all audio deliveries to ensure all audio plays at the same level on service. We raise or lower the overall mix level to ensure consistent playback between titles.

The following metering products are tested and known to be effective for ensuring conformance to our audio specifications:

Screen_Shot_2019-05-29_at_4.46.07_PM.png

The following loudness range (LRA) values will play best on the service:

  • 5.1 program LRA between 4 and 18 LU
  • 2.0 program LRA between 4 and 18 LU
  • Dialog LRA of 7 LU or less

When nearfield 5.1 mixes measure at less than 15% dialog, program-gated measurement will be used instead (-24db LKFS +/- 2 LU - ITU BS 1770-3)

For LoRo fold downs or downmixes, ITU-R BS.775-1 - 5.1 to Stereo with LFE muted is the international standard.

3.2 Peaks

We recommend setting a True Peak limiter at -2.3 for all audio deliverables. For 5.1 / 2.0, this helps to prevent false positives from minor differences in metering. For Atmos beds and objects, this setting will reduce excessive peaks due to summing factors within the Atmos renderer.

3.3 Room Setup

We recommend Nearfield mixing in rooms that approximate the size of a living room. Larger or smaller rooms can also work, when they are well-built and aligned. Use multiple microphones near the mix position which average to align rooms. Atmos rooms should be 7.1.4 at a minimum, but 9.1.6 is optimal. We suggest a moderate or light X-Curve for Nearfield, rather than the standard cinema curve. Dolby engineers are available to assist with alignment for facilities that would like it.


Change Log

2019-04-04

  • In section 3, removed loudness spec. Following it is required and not optional
  • In section 3, added current tested loudness meters
  • In section 3, revised LRA guidance to 18 for full program
  • In section 3, removed LRA guidance around difference between FX and Dialog
  • Renamed doc Sound Mix rather than Audio Mix
  • Added context in Prerequisites that audio deliverables must match camera/picture post frame rate
  • Added suggestion for a moderate or light x-curve to Best Practices
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