1. The Care and Feeding of Loudness Models J. D. (jj) Johnston Neural Audio Kirkland, Washington, USA

2. Implications? • Single band weighting filters can’t get it right. • They can get it moderately right for wideband signals with similar spectrum, where spectrum is smoothed on a critical band basis. • This means that for some “typical signals” they aren’t too far off. • There’s no mention of time here yet. • Loudness is sensed across frequency at a given time. • That’s called “partial loudness” • Getting that far is easy. NOW What?

3. The time domain • While a variety of experiments have shown that the sum of partial loudnesses is a good measure of total loudness for a given instant, there is a lack of work on what it means when either partial or total loudness varies over time. And, that is where we are today.

4. Some issues • In order to get it right, you have to know the intensity at the playback site (i.e. volume control setting, efficiency, acoustics, etc) • Good luck with that. • This creates particularly difficult issues below 500Hz. • Distortion, especially in the upper (70-120Hz) region can throw off loudness measurement by a phenominal amount.

5. Bass distortion • Consider a 90 Hz sine wave. • Harmonics at 180 and 270 • Each of those harmonics is separated by a critical bandwidth. • Remember compression? If the woofer has 20dB SNR (that would be a very good woofer), the total loudness would scale to something like • 1^1/4 + .01^1/4 +.01^1/4 = 1.63

6. The point? • Overall, loudness models for extended periods are still in development. • We don’t know if loudness or annoyance, or something else, is what people adjust volume controls for • We don’t know if it’s peak or average, or some of both • We don’t know if everyone responds in the same fashion

7. What Else? • We don’t know how well people agree on long term vs short term preferences • Some people seem to care about peak • Some care about something kinda-sorta like average • We need a system that can be adapted at the point of playback, NOT at the source. • Then, just maybe, we might get some dynamic range back