Audio Engineering Society

Chicago Section

Meeting Review, December 16, 2004

12/16/04 Meeting Highlights
by Jeff Segota

WFMT Studios hosted a Chicago Section meeting on December 16th. About thirty attendees participated in a binaural sound reproduction presentation and live demonstration by AES fellow and former president Robert Schulein. His presentation began with a discussion of the 1931-32 Bell Labs demonstration of binaural reproduction in cooperation with Leopold Stokowski, and the Philadelphia Symphony Orchestra. Two moving coil microphones, flush-mounted in a wax figure near the ears, fed an elaborate system of amplification, equalization, and earphone distribution. Although there was difficulty with front/back localization, the results were promising. Today, binaural techniques allow for more realistic sound field recreation with earphones or just two loudspeakers (although the latter requires complex cross-talk cancellation).

Mr. Schulein described a personal, portable system that allows for simultaneous binaural recording and monitoring. Miniature electret microphones are attached to insert earphones, so that the microphones are located at the ear canal entry. Careful consideration was made of the difference between the sound field sensed at the outside of a blocked ear canal versus that at the eardrum when the canal is open, and it was shown that the frequency response of this transfer function is quite independent of sound field direction. Such corrective equalization was implemented acoustically by virtue of the coupler frequency response of the earphones selected.

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Live and pre-recorded demonstrations were conducted to evaluate the technique and to show how visual and other non-auditory cues affect directional sound perception. The binaural signal was broadcast with a wireless transmitter, and each audience member was given a receiver and insert earphones. For the live examples, a volunteer was fitted with the system described above. First, Mr. Schulein spoke while walking around the room, and the audience was able to hear the sound as if he or she was sitting in the location of the volunteer. Next was a pre-recorded voice sample coming from a sequence of locations in the horizontal plane around the head, played first with the audience stationary and then with the audience physically rotating so that the virtual source remained stationary. This was followed by binaural audio/video recordings made by Mr. Schulein in Times Square, Helsinki, and on a sailboat in the British Virgin Islands. Lastly, to demonstrate music reproduction, professional violinist David Yonman performed while moving around the volunteer.

The live demonstrations generated enthusiastic discussion, and were special in that each audience member was able to experience binaural reproduction first-hand.