Tideland Prius — It's interesting that the Psychoacoustic Theory you quoted from the non-hybrid version of the "New Car Features Guide" does not appear in the hybrid version! I have done some experiments on my TCH's JBL system, and I don't believe that Toyota have actually implemented either of these "features." Note that the JBL amplifier is identical in both of the hybrid and non-hybrid vehicles.

1. Using pure tones down to below 30 Hz, I am unable to detect any sign of an attempt to create a "synthetic fundamental." The fundamental frequencies in the low-frequency range are genuine and pure. (The description given also is questionable.)
2. Careful listening tests with one-third-octave bands of noise show that the acoustical crossover frequency between the front woofers (in the front doors) and tweeters (in the dashboard near the windshield) occurs between 300 and 400 Hz. This means that musical frequencies lower than ~300 Hz come mainly from the woofers in the front doors, while frequencies higher than ~400 Hz come mainly from the tweeters by the windshield. Now, the Head Related Transfer Function (HRTF) method of elevating sounds only works in the frequency range where the outer ears ("pinnae") are effective, which is above ~1 kHz. Since all frequencies above 1 kHz come from the tweeters by the windshield, they don't need "elevating" (if they came from the door speaker that might have been a good idea).

So, I conclude that the JBL amplifier is not applying this processing to the sound, and I'm glad about this. I wonder why this irrelevant "theory" made its way into the non-hybrid Guide?

Stan