https://www.theabsolutesound.com/articles/theoretica-applied-physics-bacch-sp-adio-stereo-purifier/
Listening to music played with the BACCH-SP adio for six weeks can only be described as revelatory, in the sense that I heard a domestic two-channel system—mine—do things I’d never heard before in any setting. Two observations should be made at the start. First, as promised, the BACCH XTC filter introduced no colorations or timbral distortions to the reproduced sound. Instantaneous comparisons of filter/no filter are readily accomplished with the BACCH app on the iPad; it’s easy to toggle back and forth between the bin your filter is in and “Bypass.” The crosstalk-cancellation process is utterly transparent. Secondly, whoever did design the DAC (and ADC) for Theoretica did a helluva job. I heard no meaningful difference in the overall sound of my system when using the $47k Ideon or the BACCH-SP. Getting the model with the DAC (and ADC) requires an additional expenditure of $4000. Sounds like a bargain to me.
What does the BACCH-SP XTC filter bring to the table, sonically? The processor renders several aspects of spatiality very effectively, some of which I’ve experienced only rarely in the past with the most elite systems, if I’ve heard them at all. One is envelopment. The sonic image moved out in front of the two speakers and wrapped around the sides to end up well out into the room, outside the lateral boundaries of the Magicos. On a Chesky Records binaural recording featuring trombonist Wycliff Gordon (Dreams of New Orleans), Gordon is localized at the 10 o’clock position, forward from the plane of the loudspeakers. His improvisatory genius is believably isolated and exposed—your brain tells you that’s where he is standing as the featured performer, not where some mixing engineer put him in post-production. Music played back with the filter engaged often seems subjectively louder, perhaps because of this heightened sense of immediacy.
Envelopment and proximity are attention grabbing at audio shows but can be dismissed by skeptics as gimmicky; reverb can be taken for granted. A fourth spatial characteristic of the sound created by a BACCH filter, the one that impressed me the most, is what Choueiri has called spatial extent and resolution. Extent, he explains, “is the perception that the sound occupies a three-dimensional volume, like a hologram,” while resolution, in this context, “is the ability to discern detail and structure within the extent.” Listening to my favorite orchestral test track, the opening Allegretto of the Shostakovich Symphony No.15, as performed by Bernard Haitink and the Royal Concertgebouw Orchestra, I attended closely to the sequential woodwind solos near the beginning of the movement. It’s not only clear that the bassoon is a larger instrument than the flute, and that the former is seated a row behind the latter—you can get that kind of information from traditional stereo—but also that these correctly scaled and localized aural images interact to represent a continuous acoustic environment where the musicians are breathing the same air but still own a unique three-dimensional space of their own. It’s like the difference between the pop-up-book kind of depth and dimensionality you get from most 3D movies and the far more effortless perception of space you experience in life.