$26,000

Truly believable sonic spatialization from two channels has been compromised since the dawn of stereo by acoustic crosstalk—some sound intended for the right ear makes it to the left and vice versa. Efforts at crosstalk cancellation (XTC) began in the 1960s but fell far short until Edgar Choueiri, a Princeton University physics professor, took up the cause about 15 years ago and developed his BACCH filter (“Band Associated Crosstalk Cancellation Hierarchy.” “SP” stands for “stereo purifier”). After a unique BACCH filter is made for a listener with tiny in-ear microphones (this takes just two to three minutes), recordings played back through the XTC filter produce palpable images lateral to and behind the listener, as well as a highly credible layering of sound in front. Note that nothing is being added here: The technology is extracting information that was there all along—cues that allow for a three-dimensional representation of the original event.

It works best with binaural (“dummy head”) recordings, played back through speakers with narrow vertical dispersion, but most recordings will benefit—even artificial studio concoctions— and most speakers will deliver some of the effect. Theoretica will sell you the BACCH filter as stand-alone software (Mac only), but the BACCH-SP is a flexible and beautifully built component that can serve as a preamp—”adio” is “analog/ digital inputs/outputs.” The BACCH-SP price includes the in-ear microphones, a dedicated iPad to operate the processor, and a head-tracking camera that allows the listener to move in his or her seat without disrupting the spatialization effect. (333)