Resources For TV Channel Developers

Internet audio streaming and on-demand playback have become ubiquitous, both in consumer media and professional audio applications. Today, it is a $10 billion industry. 

Despite this popularity, the effects of excessive loudness or inconsistent loudness between sources continue to detract from the listening experience. This topic was the subject of a presentation at a recent AES seminar by John Kean, former NPR senior technologist, moderated by David Bialik of David K. Bialik & Associates.

It discussed a new AES technical document on loudness guidelines, TD1008. Kean’s presentation was followed by a panel discussion among several members of the Drafting Group.

What’s LUFS?

To measure and control loudness, engineers speak in terms of LUFS, or Loudness Units relative to Full Scale, as defined by the ITU-R BS.1770-4 Loudness Meter standard. 

LUFS relates loudness units to the maximum level that a system can handle, which is always expressed as a negative number, i.e., –18 LUFS. The less negative the number, the higher the average level. An increasing number of pro audio devices and software are equipped with LUFS metering.

Table 1 of the TD1008 recommendations covers all audio distributed by streams and podcasts as well as on-demand music services. These include audio content that is either mixed speech and music, or all music, interstitials (e.g., advertisements) and even automated voice announcements. Content where speech is measurable serves as the –18 LUFS anchor, against which music, sound effects, etc. are mixed. 

As discussed below, the document recommends that music content be album-normalized, if practical, or track-normalized to no more than –16 LUFS.

To reach the desired loudness, audio content is normalized in a downward direction if the content loudness is above the target loudness, or upward if it is below the target. The loudness of nearly all…