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Stereo question

Subject: Stereo question
From: "Scott Fraser" scottbfraser
Date: Wed Jun 20, 2007 8:40 am ((PDT))
<<In the mp3 clip http://homepages.uc.edu/~pelikas/goose.mp3 you'll
hear a Canada Goose flying from right to left. To me, when I
listen to the recording with headphones, it sounds like the goose is
flying behind me (rather than in front of me --- where it might be
seen, for example).  Am I nuts in this perception? or arbitrary? Can
anyone agree/disagree with the effect?>>

It not only appears behind me (in Sennheiser HD280 Pro headphones) it
also appears below the horizon. This is with the built-in audio
(middle of the road 24bit converter) & headphone driver (also middle
of the road, neither great nor lousy) provided in a Mac G4 PowerBook.
A high end headphone amp MIGHT reveal better directional cues &
detail, but this IS an MP3 so I wouldn't think much real improvement
is available.

<<When I reverse the channels (switch the headphones around left for
right) it STILL sounds like the goose passes behind me. So it seems
that switching left for right is a "flip" in a vertical mirror rather
than a "rotation". >>

Correct. Switching headphones around is NOT equivalent to turning
around & facing backwards. It merely changes left for right with the
same forward orientation.

<<What kind of information conveys/creates the "front/back" effect?>>

With binaural recording, artificial pinnae & a head-sized baffle
shape the sound prior to to it reaching the mics, recreating the
directional cues (HRTF, or Head-Related-Transfer-Function) provided
by our own ears & head. With headphone playback, binaural recordings
have a high degree of front-back realism. Other mic techniques are
weak in the rendering of accurate realistic front-back directional
cues, however, much of binaural's front-back realism is lost over
loudspeakers.

<<Finally, or to be less theoretical: When the recording was made, the
goose flew in front of me. What could I have done wrong?.>>

I would say the loss of data in the MP3 encoding process has degraded
the available directional information.

Scott Fraser








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