Meeting held May 8, 2010 at Old Redmond Firehouse Teen Center, Redmond, WA

	JJ Johnston
Photos by Gary Louie
PowerPoint deck

After a welcome from PNW Chair Steve Turnidge, and crowd self introductions, PNW committeeperson Dan Mortensen announced another live Frank Laico interview program for Shoreline Community College; the next AES meeting with film score recordist Shawn Murphy; and the PNW elections.

Then James (JJ) Johnston began, saying he was ex-Bell Labs and Microsoft, and now DTS chief scientist. He would cover some basic ideas about the working of the human CNS (central nervous system) and hearing, with perhaps some insight into the pitfalls of gauging sound quality with humans. While certainly not everything about the workings of the human brain is fully understood, many ideas from many researchers make some sense.

For our simplified picture, he separated the auditory system into 2 groups, the periphery (accounts for such things as HRTF (head related transfer function), cochlear analysis, and "partial loudness" after the cochlea), and the CNS. The concept of "partial loudness" needs differentiation from intensity (SPL), as loudness is a sensation level. The inner ear processes sounds to partial loudness, down the auditory nerve.

He continued with how the periphery deals with sounds, such as direction cues, cochlear processing, and transmission to the auditory nerve.

Then he spoke about the CNS processing, such as the need to switch between A-B sounds well within 200mS (with no clicks), or the ability to discern fine differences in loudness or timbre is reduced - important to know when testing audio things. Deeper in the CNS partial loudness sensations are analyzed in mono and binaural. Lots of data is lost by now, and one's memory can last seconds or so. One's analysis can be strongly guided by learning, experience and cognition.

Then auditory objects can be committed to long term memory as even more data reduction occurs. The process can be entirely steered by attention, cognition, other stimulii. So, it's very easy to be swayed in what you thought you heard. If you think something might be different, you probably will think they are different.

Thus, the nature of the human hearing process dictates that care is needed to craft scientifically valid audio comparisons like the ABX test:

• They must have a falsifiable nature (i.e. be able to distinguish between perception and an actual effect)
• They must isolate the subject from changes in other stimulii than audio (make them comfortable)
• They must be time-proximate - no clicks or gaps when switching; user controlled changeover
• There must be test Controls - (positive, negative, & anchoring elements)
• There must be trained, comfortable listeners

The applicability to Hi Fi tests that are not ABX is that if told it will sound different, it probably will, to you, and if you know something is changed, you will expect changes and refocus.

This is normal

He then played an audio demo: a music excerpt with a measured 13.6dB S/N ratio from perceptually appropriate addition of noise; then the same S/N figure, but not so clever. One sounds OK, the other not. So the raw S/N numbers mean nothing.

Audio Demo 2 was borrowed from researcher Poppy Crum - an excerpt of backwards music was played. Do you recognize the backwards sounds as words? Some do. The purported words were then shown while the backwards music was played again. Then people start to hear those words in the music. When played forwards, a familiar portion of a classic rock song was heard.

A break was held, with some door prize winners: DTS ball caps: Rene Jaeger, Ray Wallace, Jonathan Christian, Tom Stiles

The meeting continued with visiting the websites of strange audio products claiming unusual performance at high prices, with much discussion of the products.

A special thanks to Ken Wong, Teen Program Director for the City of Redmond, which runs the Old Firehouse Teen Center.

Reported by Gary Louie, PNW Section Secretary

Last modified 02/06/2015 0:56:5.