What Should (or Shouldn’t) a Loudness Tool Do?
What Should a Loudness Tool Do?
The requirement is to be able to analyse the audio, check for compliance and attenuate / normalise without any degradation of audio quality, and where audio is embedded within a video source signal or file, video is in no way degraded.
1. Measurement
First of all any loudness compliance tool must be measured to see whether or not it complies. But complies with what? Broadcasters are incorporating loudness compliance in their delivery specifications. Every Broadcaster bases the delivery specification around locally required standards. There are additional challenges to international content providers to provide deliverables not just to standards, but also national variance within the application of those standards. Any tool should therefore have the flexibility to create custom profiles based around the required standards.
2. Reporting
It is always useful to generate a report, which shows the measurements and attributes of a particular file. Either a written detailed report defining metrics for the specific file, or a graphical representation for the specific file are needed. It’s useful to have both types of reports.
3. Correction
As well as measurement it is desirable for the compliance tool to correct the detected errors. Industry feedback suggests that:
- Fixing should be strictly attenuation or normalisation. The audio fixing process must maintain the integrity of the original mix.
- The fixing or processing of audio essence embedded within video files must NOT affect the integrity of the video or metadata essence.
- We should consider delays in start of real essence (tone & bars, black & silence) and duration.
Loudness is a newer measurement, and attempts to put a figure on ‘how loud’ the material appears to be to a listener. How a person ‘hears’ the loudness is based on many factors, such as type of programme material, the listeners mood and health, and whether they like the programme material, so it is quite subjective. The Loudness measurement attempts to put a number on how an average listener might respond to the programme material.
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