We are being asked to measure the maximum ITU loudness reading with a maximum peak of 0 dB, with the reference level set to – 20 dBFS and the rolling integration window set to 3 seconds. The Peak programme meter type IIa should not register over 6PPM. How do I configure this?
Set the LU reference to -20LFS - the 12 o'clock position in the Radar on the external circle corresponds to the reference.
Set the peak indicator to -10 dBFS ( = PPM6) In fact you could allow for 2 extra dB, and have maximum at -8 dBFS when using the True-peak meter. Sticking to -10 dBFS even on a True-peak meter would be conservative.
Sliding window is 3 seconds on LM5D
With regards to the sliding window, EBU R128 specifies 3 sec, Dolby uses 10 sec, ITU BS.1770 isn't specific. The difference between 3 and 10 sec vanishes with programmes over a certain duration, but is significant with shorter programmes such as promos and commercials. In such cases, 3 sec is far superior when it comes to prevent annoyingly loud sounds.
Here is the method for using the LM5D:
The Centre of Gravity descriptor is programme duration and not bound to a sliding window size. BS.1770 only specifies programme loudness and not the sliding window discussed above, while EBU R128 generally provides more tools and specifies both. The main application for this kind of descriptor is for programme normalization and/or setting of metadata in AC3. For example, if a commercial measures -20.3 LFS top to tail, and your station target level is -23.0 LFS, you can apply a static -2.7 dB gain offset to make it right on target.
- If your customer's current specification is max -20 LFS based on a sliding 3 sec window, you need to adjust the level of a programme so you never enter the yellow area of the radar when 0 LU is set to -20 LFS.
- If your customer's specification is based on programme loudness, you instead need to limit the average loudness of the program to -20 LFS. In that case, Centre of Gravity should be used.
Note that 1) is better at restricting loud events inside a programme than 2). I therefore believe BCAP rules, in order to limit annoyance from commercials, make use of 1) rather than 2).