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Broadcast Wave Format (BWF)

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Broadcast Wave Format (BWF) is extension of Microsoft WAV audio files. Read about BWF destination, content, other.

Destination

BWF is special additional chunk that allow:

- add more information for music production applications;

- information to unite number audio files in single stuff (see 'time reference' below);

- information about loudness level of the audio file content for level normalization in broadcast applications.

Also, there is Multi-channel Broadcast Wave Format (MBWF) that is intended to storing of multichannel files with size above 4 GByte inside RF64 format.

 

 

 

Versions

Version 0

      - description of the sound sequence;

      - name of the originator;

      - reference of the originator;

      - origination date;

      - origination time;

      - first sample count since midnight (time reference);

      - version of the BWF;

       - reserved data;

       - History coding.

      Contain description of coding process applied to the audio data. Each new coding application shall add a new string with the appropriate information. AuI ConverteR 48x44 according EBU R98 add "A=PCM,F=44100,W=16,M=mono,T=AuI ConverteR 48x44," string, where:

       A - Coding Algorithm;

       F - Sampling frequency, Hz;

       W - Word Length, bits;

       M - mode;

       T - free text. 

 

Version 1

UMID for audio file into reserved data area is added.

       - SMPTE UMID.

       UMID (Unique Material Identifier) is a special code that is used to identify audiovisual materials (locally generated and globally unique identifier, standardised by the Society of Motion Picture and Television Engineers (SMPTE)).

 

Version 2

Loudness measurements for audio file into reserved data area is added.

For regularize of values of loudness for different broadcast programmes (as example, ads and film) need normalize loudness of audio files. Audio files must contain its measured level of loudness also. Used algorithm for objective estimation of subjective loudness (for different program's genre).

  • Integrated Loudness Value of the file in LUFS (measured by AuI ConverteR 48x44 according with ITU-R BS.1770-2) for multichannel files also;
     
  • Loudness Range of the file in LU (measured by AuI ConverteR 48x44 according with EBU – TECH 3342);
     
  • Maximum True Peak Level of the file expressed as dBTP (while not measured by AuI ConverteR 48x44);

        Analog Digital Converter can bypass some peaks of level input signal. Then make oversampling possible restore this peaks: appear increasing of signal level (max 0.688 dB - see Rec. ITU-R BS.1770-2, p. 21).

  • Highest value of the Momentary Loudness Level of the file in LUFS (measured by AuI ConverteR 48x44);
     
  • Highest value of the Short-Term Loudness Level of the file in LUFS (measured by AuI ConverteR 48x44).

 

 

BWF compatible converter

AuI ConverteR 48x44

RF64 converter audio

 

 


References

Format specifications

  1. EBU Tech 3285 - Specification of the Broadcast Wave Format (BWF) - Version 1 - second edition (2001)
  2. EBU Tech 3285-s1 - Specification of the Broadcast Wave Format (BWF) - Supplement 1, MPEG Audio - first edition (1997)
  3. EBU Tech 3285-s2 - Specification of the Broadcast Wave Format (BWF) - Supplement 2, Capturing Report - first edition (2001)
  4. EBU Tech 3285-s3 - Specification of the Broadcast Wave Format (BWF) - Supplement 3, Peak Envelope Chunk - first edition (2001)
  5. EBU Tech 3285-s4 - Specification of the Broadcast Wave Format (BWF) - Supplement 4, Link Chunk - first edition (2003)
  6. EBU Tech 3285-s5 - Specification of the Broadcast Wave Format (BWF) - Supplement 5, <axml> Chunk - first edition (2003)
  7. EBU Tech 3352 - The Carriage of Identifiers in the Broadcast Wave Format (BWF) (2012 Recommendation)
  8. BWF Metadata editor

 

Loudness measurement

  1. Loudness normalisation and permitted maximum level of audio signals (EBU – Recommendation R 128)
  2. Algorithms to measure audio programme loudness and true-peak audio level (Recommendation ITU-R BS.1770-3)
  3. Loudness Range: A measure to supplement loudness normalisation in accordance with EBU R 128 (EBU – TECH 3342)
  4. Practical guidelines for Production and Implementation in accordance with EBU R 128 (EBU – TECH 3343)
  5. Format for the <CodingHistory> field in Broadcast Wave Format files, BWF (EBU Technical Recommendation R98)
  6. Test files for control measurement instruments (Compliance material for Recommendation ITU-R BS.1770. Report ITU-R BS.2217)

 


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