Dave Moulton

Alert readers may recall that for the past year I’ve been devoting most of this column to the CALM Act and the related issue of audio levels and loudness in broadcast television audio.

Dave Moulton takes another look at TV audio levels in advance of the CALM Act next month.

We also seem to have fractured our physical audio delivery systems into four distinctly different genres, all served by the same HD digital audio feed embedded in our productions.

You may recall that we’ve been grappling with the measurement of audio loudness and the implications of the ITU’s B.S. 1770-1 standard for the measurement of loudness, in support of the CALM Act.

I don’t know how many TV Technology readers know of Neil Muncy. However, it is highly improbable that any of us haven’t heard his work.

“I’m a TV engineer from the old school, so of course I never read articles about audio. The CALM Act changes that, of course.”

One major determinant of timbre is the distribution of energy across the audio spectrum.

There can be hundreds of overtones present in a particular note or sound.

My measurements sought to examine the question of variance of audio levels between channels and how this variance has changed (or not) over time.

It seems appropriate to me that we go a little further with the discussion, simply to clarify what seems to be meant and desired in practice by A/85 and its authors.

Their performance and effectiveness can be highly variable for a range of not-so-obvious reasons.

There are issues of dynamic range, maximum and minimum levels, subjective loudness qualities, spectrum and much more.

This will actually take a couple of columns. I'll start with the idea of standing waves.

The first thing to keep in mind is that we are talking about a pair of signals here, not a single mono signal.

You may recall I've been ranting about variance in loudness levels on broadcast television for numerous years.

The protocol is for modifying the television audio signal to measure its magnitude in a way that more closely agrees with humans' subjective sense of loudness

This process will have the effect of making your mixes clearer, more transparent, a little louder for a given maximum level and generally a little "nicer.

In this follow-up column I will reveal to you how to enhance and polish that sound once the warts are gone, or at least reduced.

24 dB below Full Scale (zero LKFS) is the new mandated nominal, or "target," level for audio broadcast.

We would like all equipment to play back at the same calibrated level, including in our viewers' homes. To achieve that, we use a protocol called dialnorm.

Not all crumminess sounds the same.

Our perception of loudness varies as a function of amplitude, frequency, frequency bandwidth and time. It is a complex sensation.