BACCH Prelude

Professor Edgar Choueiri (Eames chair) and Buddy Gardineer setting me up with BACCH 3D

"Getting measured for head-tracking for use with BACCH 3D." is the answer to Monday's 'Guess What I'm Doing' .gif quiz (as some astute readers correctly surmised). The real point is that I've been listening to BACCH 3D in-barn for a few days and I have a few important things to tell you.

screen shot of part of the BACCH-dSP software screen showing head-tracking and 3 'bins' for saved listener profiles.

1. It Works
There is no question that BACCH 3D works. This is not conjecture, this is a fact.

2. What Does BACCH 3D do?
In my simplest terms, BACCH 3D eliminates crosstalk 1 (see the Q&A for a more detailed definition and a discussion of BACCH 3D Sound), thus allowing the spatial information captured in stereo and binaural recordings to be reproduced with extreme accuracy.

3. Really?
Yes, really.

4. How Does it Do That?
I cannot answer this question but we will be posting a video interview with BACCH's creator, Professor Choueiri, on this subject and there's a Q&A at the end of this post that should answer some questions.

5. How Much Does It Cost?
The BACCH4Mac Audiophile package which includes the BACCH-dSP software, the BACCH-BM microphones, and the RME audio interface, and which I'm reviewing, starts at $4,980.


Everything Matters (to varying degrees)
I very much enjoyed Stephen's story on the importance of contact cleaning and John Darko's thematically related piece "Experience Matters". And I agree with the common hi-fi clause, "everything matters", and I agree even more if we add "to varying degrees". Some people, I'll call them biased, believe that everything in hi-fi is Santa Claus. To which I'll respond as Groucho Marx and suggest they are in need of a sanity clause.

In any event, the degree to which BACCH 3D changes the sound of my system is among the most apparent and dramatic changes I've experienced. So far. So much so that the addition/insertion of a Mac mini (running BACCH4Mac software and Roon) and the RME Babyface Pro A/D D/A converter do not degrade the sound of my O-so-carefully crafted system. To clarify, the Mac mini/Bayface replace my dCS Network Bridge, and instead of going AES out of the dCS to my totaldac, I'm going Toslink out of the Babyface into the totaldac. With a generic Toslink cable, no less, and everything is being converted to 24/96 before the totaldac gets its loving hands on it.

Sacré bleu! Sacrilege!

"To varying degrees."

My initial thoughts on this seeming contradiction is that BACCH 3D imparts such a dramatic change in the sound of my system, that the degree to which things like cables and Roon endpoints pale in comparison. I will test this further over time and report my final findings in my review.

The RME Babyface Pro is currently the only device supported by Theoretica Applied Physics, the company behind BACCH. Its main purpose and reason for being is two-fold; BACCH ships with in-ear microphones which are used to measure, and set in software, your ear/head/movement (as seen in that "guess what I'm doing" .gif). Part two is its loop-back feature which allows for real-time processing letting BACCH 3D move with you so that the 3D image remains accurate if/when you move.

You lookin' at me? ... Well, I'm the only one here. You lookin' at me?”

Of course users are free to insert their own A/D D/A solution and the well-heeled audiophile can opt for the hardware-based BACCH solutions, thus eliminating a rather inexpensive piece of very well made pro audio hardware. After this review, I will be reviewing the BACCH-SP dio (one of the hardware-based solutions).

The other note to note, which also falls under "to varying degrees", is the degree to which BACCH presents a 3D image. This degree is dependent on the recording (if there's another hi-fi clause you can count on it's "the quality of the recording matters") which I place directly under "the quality of the music matters most." Feel free to move these around but the more you do, the less happy you'll become.

Binaural recordings, like the ones you can get from Chesky Records/HDtracks are reproduced with pin-point accuracy placing the musicians in your room where they were in the room in which they were recorded. That room is also reproduced with uncanny realism in your room. Regular old stereo recordings, especially those with spatial information, are reproduced with uncanny realism.

My initial impressions—BACCH 3D makes everything I've listened to through it sound more natural.


1. Crosstalk cancellation—when sound from the left speaker goes in your right ear and vice versa, thus cancelling out spatial information contained in the recording (a better description)


BACCH 3D Q&A
Professor Choueiri provided the following Q&A that should help answer some of your questions.

1 What is BACCH 3D Sound?
3D Sound is a recent breakthrough audio technology (licensed by Princeton University) that yields unprecedented spatial realism in speaker-based audio playback allowing the listener to hear, through only two loudspeakers, a truly 3D reproduction of a recorded soundfield with uncanny accuracy and detail, and with a level of high tonal and spatial fidelity that is simply unapproachable by even the most expensive and advanced existing high-end audio systems.

BACCH 3D Sound relies on canceling an undesired artifact, called crosstalk, that occurs whenever stereo sound is played through loudspeakers, thus allowing the 3D cues which the brain needs to hear in 3D, and which exist in abundance in practically all well-made stereo recordings, to naturally reach the brain of the 2listener.

2. How Does BACCH 3D Sound differ from surround sound?“
BACCH 3D Sound has nothing to do with surround sound. Surround sound, which was originally conceived to make the sound of movies more spectacular, does not (and cannot) attempt to reproduce a true 3D soundfield. What 5.1 or 7.1 surround sound aims to do is provide some degree of sound envelopment for the listener by surrounding the listener with five, seven, or more loudspeakers. For serious music listening of music recorded in real acoustic spaces, audio played through a surround sound system can at best give a sense of simulated hall ambiance but cannot offer an accurate 3D representation of the soundfield.

In contrast, BACCH 3D Sound’s primary goal is accurate 3D soundfield reproduction. It gives the listener the same 3D audio perspective as that of the ideal listener in the original recording venue1. Soundstage "depth" and "width", concepts often used liberally in hi-end audio literature to describe an essentially flat image (relative to that in BACCH 3D Sound), become literal terms for BACCH 3D Sound. If, for instance, in the original soundfield a fly cicrles the head of the ideal listener during the recording, a listener of that recording played back through the two loudspeakers of a BACCH 3D Sound system will hear, simply and naturally, the same fly circling his or her own head. If, in contrast, the same recording is played through standard stereo or surround sound systems the fly will be perceived to be inside the loudspeakers or, through the artifice of the phantom image, in the limited vertical plane between the loudspeakers.

3. Does BACCH 3D Sound require special speakers?
BACCH 3D Sound will greatly enhance the spatial fidelity of sound reproduction through any loudspeakers. Loudspeakers that have high sound directivity2 will give the best and most accurate 3D imaging in a room with little or no sound treatment, as room reflections, which degrade the imaging, are minimized by such loudspeakers.

However, even loudspeakers with low directivity (i.e. omni-directional loudspeakers) will give a spectacularly wide soundstage with BACCH 3D Sound in a typical listening room. As the importance of room reflections is decreased (by increasing the ratio of directed/ to eflected sound through room treatment and/or higher-directivity speakers) the image’s depth and 3D imaging approach the depth and spatial characteristics of the original soundfield.

An ongoing investigation of speaker directivity at the 3D3A Lab, has shown that dipole speaker designs, electrostatic speakers, as well as speakers with horns and waveguides offer significant advantages in 3D imaging with BACCH 3D Sound in highly reflective rooms, as they increase the ratio of direct to reflected sound. Abating room reflections with physical room treatment (i.e. using sound absorbers on sound-reflective surfaces) in a listening room is always beneficial to any audiophile-grade sound system. For BACCH 3D Sound the effect of sound treatment is equivalent to using loudspeakers with high directivity. The more directive the loudspeakers are, the less sound treatment is needed for BACCH 3D Sound to produce a full and accurate 3D sound image.

Therefore, in a reflective untreated listening room, directive loudspeakers are more desirable. In a well treated listening room with sound-absorbing surfaces, any loudspeakers, even omnidirectional ones, will produce an excellent 3D image.2

4. How does BACCH 3D Sound work?
Imagine a musician who stands on the extreme right of the stage of a concert hall and plays a single note. A listener sitting in the audience in front of stage center perceives the sound source to be at the correct location because his brain can quickly process certain audio cues received by the ears. The sound is heard by the right ear first and after a short time delay (called ITD) is heard by the left ear. Furthermore there is a difference in sound level between the two ears (called ILD) due to the sound having travelled a little longer to reach the right ear, and the presence of the listener’s head in the way. The ILD and ITD are the two most important types of cues for locating sound in 3D and are to a good extent preserved by most stereophonic technique3.

When the stereo recording is played through the two loudspeakers of a standard stereo system, the ILD and ITD cues are largely corrupted because of an important and fundamental problem: the sound recorded on the left channel, which is intended only for the left ear, is heard by both ears. The same applies to the sound on the right channel. Consequently, an audiophile listening to that recording on standard stereo system will not correctly perceive the musician to be standing on the extreme right of the stage but rather at the location of the right speaker. Consequently the perceived soundstage is mostly confined to an essentially flat and relatively limited region between the two loudspeakers irrespective of the quality and cost of the hardware in the standard stereo system—the 3D image is greatly compromised4.

In order to insure the correct transmission of the ILD and ITD cues to the brain of the audiophile, the sound from the left loudspeaker to the right ear, and that reaching the left ear from the right loudspeaker (called "crosstalk") should be cancelled.

The technique of crosstalk cancellation (XTC) has been known for some time and can be applied by filtering the recorded sound through an XTC filter before feeding it to the speaker. This can easily be done digitally. However, until recently, XTC filters have had a detrimental effect on the sound as they inherently add a strong spectral coloration to the processed signal (i.e. they severely change the tonal character of the sound). This is why, until the advent of BACCHecently, XTC had not been widely adopted by stereo manufacturers and audiophiles.

BACCH 3D Sound is based on a breakthrough in XTC filter design, that allows producing optimized XTC filters, called BACCH 6 filters, that add no coloration to the sound for a listener in the sweet spot (or even outside of the sweet spot). Not only do BACCH filters purify the sound from crosstalk, but they also purify it from aberrations by the playback hardware in both the frequency and time domains.

The result is a 3D soundstage with a striking level of spatial and tonal fidelity never experienced before by audiophiles.

5. What are BACCH Filters?
There are two types of BACCH filters. The individualized BACCH filter (sometimes called i-BACCH) is custom-made using in-situ acoustic measurements of the audiophile’s entire listening chain, including his hi-fi hardware, loudspeakers, head, torso and ears. It is designed by sending special test tones through the hi-fi chain and recording the sound with miniature microphones placed at the entrance of the audiophile’s ear canals as he is sitting in a sweet spot of his choice. It takes about one minute to do this measurement. Theoretica’s BACCH-SP processor and BACCH-dSP application allow users to easily produce individualized BACCH filters for their systems.

The universal BACCH filter (called u-BACCH) is the same as i-BACCH except a special dummy head, having microphones in its ears, is used to make the measurements instead of the audiophile’s own head and ears. A u-BACCH filter yields a bit less accurate 3D image then i-BACCH when used by the audiophile himself to listen to his hi-fi system, but is more compatible with other listeners (who do not have i-BACCH filters designed for them). Since the dummy head was designed to represent the sound diffraction characteristics of an "average" human head, the difference between the sound through the two types of filters is subtle but perceivable by a discerning audiophile. 6BACCH stands for "Band-Assembled Crosstalk Cancellation Hierarchy"—a name that represents the mathematical filter design method and pays tribute to the great composer with a similar sounding name.5

Is BACCH 3D Sound compatible with existing stereo recordings?
Yes. Unlike other 3D audio techniques all of which require nonstereophonic recording techniques and coding, and many more than two loudspeakers for playback, BACCH 3D Sound is fully compatible with all existing stereo recordings, and requires a single pair of loudspeakers.

In fact, virtually all stereo recordings contain 3D cues that are corrupted by standard stereo playback (see discussion in Q&A 4). BACCH 3D Sound simply allows these 3D cues to reach the brain of the listener. Therefore an audiophile can delight in re-listening to his existing collection of recordings through BACCH 3D Sound and discover the striking spatial and tonal fidelity that was missing or marred by standard stereo playback.

7. Is the 3D realism of BACCH 3D Sound the same with all types of stereo recordings?
The stereophonic recording technique that is most accurate at spatially representing an acoustic sound field is, incontestably, the so-called "binaural" recording method6, which uses a dummy head with high-quality microphone in its ears7. Until the recent advent of BACCH 3D Sound, the only way for an audiophile to experience the spectacular 3D realism of binaural audio was through headphones. Many such recordings exist commercially, and more have recently been made thanks to the recent rise in the popularity of headphones.

BACCH 3D Sound shines at reproducing binaural recordings through two loudspeakers and gives an uncannily accurate 3D reproduction that is far more stable and realistic than that obtained by playing binaural recordings through headphones8.

All other stereophonic recordings fall on a spectrum ranging from recordings that highly preserve natural ILD and ITD cues (these include most well-made recordings of "acoustic music" such as most classical and jazz music recordings) to recordings that contain artificially constructed sounds with extreme and unnatural ILD and ITD cues (such as the pan-potted sounds on recordings from the early days of stereo). For stereo recordings that are at or near the first end of this spectrum, BACCH 3D Sound offers the same uncanny 3D realism as for binaural recordings10. At the other end of the spectrum, the sound image would be an artificial one and the presence of extreme ILD and ITD values would, not surprisingly, lead to often spectacular sound images perceived to be located in extreme right or left stage, very near the ears of the listener or even sometimes inside of his head (whereas with standard stereo the same extreme recording would yield a mostly flat image restricted to a portion of the vertical plane between the two loudspeakers).

Monaural recordings contain very little, if any, spatial information11 and thus are not well suited for with BACCH 3D Sound. Therefore, it is best to bypass BACCH processing for mono recordings11

Luckily, many of well-made popular music recordings over the past two decades have been recorded and mastered by engineers who understand natural sound localization and construct mostly natural-like stereo images, albeit artificially, using realistic ILD and ITD values. Such recordings would give a rich and highly enjoyable 3D soundstage when reproduced through BACCH 3D Sound.

8. Is BACCH 3D Sound compatible with analog audio?
Yes. The BACCH-SP Sound processor accommodates (balanced or unbalanced) stereo analog inputs and outputs. Since the BACCH filter is a digital one and must be applied in the digital domain, the input analog signal is converted to a high-resolution using audiophile-grade A/D converters inside the processor. The processed digital signal can then be sent out as a digital signal (e.g. for an outboard converter or a digital speaker) or converted to analog using an audiophile-grade D/A converter inside the processor.

9. Why call it "BACCH 3D Sound"?
The word "stereo" was always associated with three-dimensional objects or effects until its later use, in the 1950s, in the word stereophony, which, ironically, is now a term that does not invoke true three-dimensional sound in the popular mind12. In fact, the earliest use of "stereo", which comes from the word Greek στερες, (stereos) which means solid, goes back to the 16th century when the term stereometry was coined to denote the measurement of solid or three-dimensional objects. This was followed by stereographic (17th c.), stereotype (18th c.), stereoscope (19th c.) (a viewer for producing 3D images), and stereophonic (circa 1950). Stereophonic sound, alas, remained a poor approximation of 3D audio until the recent advent of BACCH 3D Sound, which restores to the word stereo its original 16th century 3D connotation.

The epithet "pure" in "BACCH Stereo Purifier" refers to the purifying action of the BACCH filters, which are at the heart of BACCH 3D Sound. A BACCH filter "purifies" the sound from crosstalk for playback on loudspeakers, without adding coloration, and purifies it also from the detrimental effects of spatial comb filtering and non-idealities of the listening room, the loudspeakers and the playback chain.


1. By the "ideal listener in the recoding venue" we mean the actual main stereo recording microphones, or the left and right channels of the stereo master recording, which represent the left and right ear of the ideal listener in the original soundfield.
2. Sound directivity is the extent to which loudspeakers beam the sound towards the listener instead of broadcasting it in all directions around the room.
3. They are most accurately preserved if the recording is made with a dummy head (see Q&A 7).
4. Aside from greatly compromising the 3D image, standard stereo (and even more, surround sound), inherently suffers from the problem of comb filtering, which significantly alters the tonal content of sound, and which is due to the interference of sound waves emanating from more than one speaker.
5. BACCH stands for “Band-Assembled Crosstalk Cancellation Hierarchy”—a name that represents the mathematical filter design method and pays tribute to the great composer with a similar sounding name.
6. The accuracy is due to the fact that binaural audio preserves not only the correct ILD and ITD cues discussed in Q&A4, but also contains so-called “spectral cues,” which are the effects the torso, head and ears have on the frequency response and which the brain uses, in addition to ILD and ITD cues, to locate sound, especially at higher frequencies.
7. The spatial accuracy of dummy head recording is only surpassed by recordings made with microphones placed in the listener’s own ears—alas, a rare commodity that would have benefits upon playback for only that listener.
8. This is because binaural playback through headphones or earphones is very prone to head internalization of sound (which means that the sound is perceived to be inside the head) and requires, in order to avoid this problem, an excellent match between the geometric features of the head of the listener and those of the dummy head with which the recording was made (This problem is surmounted by the BACCH-dHP module of the BACCH-dSP software). BACCH 3D Sound does not suffer from this problem as the sound is played back though loudspeakers far from the listener’s ears.
9. The 3D realism is the same although the ability of reproducing a sound source at a location that accurately corresponds to the original location is relatively decreased due to the absence of spectral cues.
10. They contain no ILD, ITD or spectral cues but may contain some distance cues in the relative magnitude of the ratio of direct-to-reflected sound of the recorded sound sources.
11. Some stereo recordings have overwhelmingly strong mono content and may not yield much of an improvement in spatial realism when processed through BACCH.
12. Despite the tendency of some audiophiles and audio reviewers for describing the sound from certain hi-fi components as “three-dimensional” or ”holographic”.

COMMENTS
bobflood's picture

Really cool to see that there still are people who think that accurate reproduction of music is a worthwhile pursuit.

insertusernamehere's picture

Very interesting, I'm looking forward to your continued exploration of this tech. I looked at the software-only product on the BACCH website it seemed like the "best" playback chain would be Mac computer -> USB -> DAC, bypassing the Bayface completely (except for filter creation). Is there a reason you left the Bayface and Toslink in your playback chain? Also, what about playback software? Can you "point," say, Roon or JRMC at BACCH as an output device? Thank you.

Michael Lavorgna's picture
...is for real-time head tracking. This way, the 3D image remains stable if you move around (left to right).

If you remove real-time head tracking, the 3D sweet spot is the center position. If you move outside that spot, you get regular old stereo. I plan to explore this option, and others, in the review proper. [See Buddy's response below, Ed.,]

The answer to your second question is yes for Roon, which I'm using to control playback (Roon Bridge is loaded on the Mac mini).

insertusernamehere's picture

... I assumed that the head tracking functionality resided in the Mac, not in (or at least via) the Babyface; I guess the BACCH hardware solutions avoid this problem, though at prices way out of my league. This seems very unfortunate. Though if, as you say, the juice is worth the squeeze....

Michael Lavorgna's picture
...the software does reside on the Mac mini (Bacch4Mac) but the Babyface is needed to receive the real-time movement data from the camera and send it to the Mac mini (Bacch4Mac). [I should trace cables before typing. See Buddy's response below, Ed.]

I will be trying out listening without the Babyface and see how critical it is.

bgardineer4's picture

Hi, this is Buddy with Theoretica. Just to clarify, there are indeed two options to hook BACCH4Mac to an outboard DAC. We simply chose one: optical from the RME interface to the DAC. We could have easily chosen the other option: USB from the Mac to the DAC. We've tested both options with various DACs and have found no audible difference, which is not very surprising as both options are using the same D/A conversion.

Regarding head tracking, the camera actually connects directly to your Mac via USB (and for desktop listening, you can even use the internal webcam of your iMac or Macbook Pro). The main function of the Babyface Pro in the system is to allow, through its excellent mic preamplifiers and a high-precision A/D converter, the use of the BACCH-BM microphones for the calibration process that creates the BACCH filters.

The Don's picture

I do think some mention needs to be given to Ralph Glasgal at Ambiophonics.org who has been talking about this for years and years. His work shop in North Jersey is something else, one of those demos you don't forget. On his Website for a mere 10 bucks you can download a VST file to drop into JRiver etc. to get a taste of what this all about.

Michael Lavorgna's picture
There are many people, researchers, and companies working in this field for years (and years). Ambiophonics is but one approach.

See 3D Audio Effect

PeterMusic's picture

How wide is the "sweet spot"? My speakers are 8' apart. Instead of sitting about 8' away from their midpoint, equidistant from the speakers, I often sit about 8' away, directly in front of the left or right speaker. Will I still get the 3D effect?

(I know this is way suboptimal, it's a complex social negotiation in our house.)

Michael Lavorgna's picture
...you create profiles for each position. You can see in the screen shot image in the post that the Bacch software allows for 3 "bins' or profiles. I'm assuming you could create a separate profile for each listening position so that you get the full/accurate 3d image in each position.

That being said, this is something I have not discussed with the people at Theoretica so there may be a better way to accomplish this same thing.

PeterMusic's picture

Thanks! Very excited about this

blang11's picture

I'm psyched for this review. Sounds like the better the recording, the better this tech works. Binaural recordings will be most realistic, and high quality audiophile stereo recordings will also work well. I'm most curious to hear your impressions of stereo recordings of just average quality. Rock, pop, and the like.

Michael Lavorgna's picture
The better the hi-fi works ;-)

I can say with utmost certainty that Jimi Hendrix's "Electric Ladyland" and Einstürzende Neubauten's "Tabula Rasa" sound simply amazing.

PeterMusic's picture

So I'm explaining to me rock musician son how cool this all is, and he asks--But if in a live show the whole thing is going through amps, and the vocals are going through a PA, isn't the spatial effect already messed up? (Kids today are so damn irritating.)

Thoughts on this? Thanks

Michael Lavorgna's picture
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CheeHing's picture

Professor Choueiri said : "...When the stereo recording is played through the two loudspeakers of a standard stereo system, the ILD and ITD cues are largely corrupted because of an important and fundamental problem: the sound recorded on the left channel, which is intended only for the left ear, is heard by both ears..."

On the face of it, these assertions by the good professor are puzzling. Isn't it the essence of stereophony that both ears hear both loudspeakers ? If the BACCH system actually attempts to convert ( on the fly) normal stereo recordings to binaural recordings for playback on loudspeakers, then these assertions would make sense ( to me).

Michael Lavorgna's picture
In the quote you provided, Professor Choueiri is not talking about *all sound from the left channel...* rather those that are "recorded on the left channel". The stereo image also has sounds which originate from both channels, like the center images.

I'm also not so sure there's any way to "convert a normal stereo recordings to binaural recordings for playback". True binaural recordings will be reproduced with great accuracy through BACCH so the 3D effect will therefore be much more pronounced as compared to a stereo recording.

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