Broadcast Wave Format (BWF)
Broadcast Wave Format (BWF) is extension of Microsoft WAV audio files for its description. BWF have three versions: 0, 1 and 2.
Versions
1. Version 0
- description of the sound sequence;
- name of the originator;
- reference of the originator;
- origination date;
- origination time;
- first sample count since midnight;
- 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.
2. Version 1: Add UMID for audio file into reserved data area
- 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)).
3. Version 2: Add loudness measurements for audio file into reserved data area
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).
Converter compatible
48x44's PRO measure audio stream (mono, stereo, multichannel) loudness and write it into BWF chunk of WAV file.
References
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.1770-2)
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)
