AES Section Meeting Reports

Pacific Northwest - January 29, 2014

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The PNW Section January 29, 2014 meeting presented James D. (JJ) Johnston talking about the confusing issue of audio dynamic range. In addition, Bob Smith added a demonstration of software for measuring and displaying various interpretations of level or loudness on a DAW. Johnston is a current Governor of the AES and an AES Fellow, and one of the inventors and standardizers of MPEG 1/2 audio Layer 3 and MPEG-2 AAC. Smith is an audio engineer with Physio Control and runs BS Studios.

About 60 attendees, about 23 AES members amongst them, gathered at the Digipen Institute of Technology in Redmond, WA.

JJ set about to clarify some of the issues trying to describe dynamic range. He discussed problems quantifying numbers while dealing with perceptual response, as well as non-perceptual devices.

For one, there are few standards. Often, numbers are bandied about that have little correlation to the process being described, or are really inadequate.

He went into loudness (a sensation level) vs. SPL, intensity, and other strict definitions. Should you measure peak levels vs. noise floor? What about RMS levels? What about levels that are frequency dependent?

A single number is basically inadequate to really tell much. JJ would prefer seeing a graph of frequency vs. peak and noise floor levels. This would be the best way to determine proper gain structure in a system. And "A" weighting is wrong here.

With perceptual work, the issues of dynamic range are even murkier. Short and long term dynamics come into play. He spoke about the television issues of the CALM Act, and the BS1770 loudness spec. Using sones or phons would be fine for perceptual measurements, which can't and won't correlate to a simple dB number.

JJ showed several graphs of music samples' dynamic range, using open-source software (Octave). The scripts were placed online so participants could experiment themselves. Examples of vintage rock, modern pop and classical music were shown.

After a break, door prizes were awarded to:

Fluke Voltlight (courtesy Rick Rodrigues/Fluke) - Steve Wilkins
vintage JAES on PCM (courtesy Scott Mehrens) - Ed Gruse
Nature photos by JJ - Hubert Oliver, Christopher Deckard, Robb Riggs
JAES loudspeaker anthology (Mehrens) - Dave Ellis, Jake Muir
Desktop Mastering book (courtesy the author/Steve Turnidge) - David Lucavish
Amprobe thermometer (Fluke) - Thornton Prime
Meterman DMM (Fluke)- Jeremy Anderson

After the break and prize awards, Bob Smith (Physio Control; BS Studios) presented on products available to display "loudness" levels on your DAW. Included were:

-VU meter (PC simulation)
-PPM (peak program meter)
-Dorrough Loudness Meter
-TT Dynamic Range Meter
-TC Electronics "radar" display showing LUFS and other info on one display

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AES - Audio Engineering Society