Bacch Dsp, True stereo?

It's not a new fad. Ralph Glasgal has been promoting DSP crosstalk reduction for a long time. Polk, Carver, Lexicon and others have tried to tackle the crosstalk problem over the years using analog methods. It's a real problem, a real shortcoming of 2 speaker stereo reproduction. It's not intentional or desirable in any way, although some may develop a taste for it. 2 speakers is the simplest stereo possible and it beats mono, so that's why it became a standard. It has nothing to do with any inherent audio superiority, although with crosstalk reduction it can get so good on properly made recordings that it's harder to argue the need for multi-channel formats. Still, I think well done up-mixing of stereo recordings to 5 or 7 speakers located across the front of the listening area has some great upside potential, especially for creating a huge sweet spot. Purpose made recordings for this kind of setup would even be better, but that's not likely to happen.

Adding crosstalk to headphones may make some sense, but ideally you would not want to do it with the same time delay that happens across your head with stereo speakers. If you do so, you'll introduce massive comb filtering to the signal for center panned sounds, just like speakers do to your ears. Now that I say that, I can think of a way to add time delay without causing comb filtering to center panned sounds - I think I'll have to try that!

I've not tried the BACCH DSP yet, but I'll vouch for crosstalk reduction. From the reviews I've read of BACCH it sounds similar to my own experiences with using a physical divider or my own, not so powerful channel mixing methods. The timbre of center panned sounds is very nicely improved, as is the overall sense of acoustic space. It matters more on some recordings than others. I never heard anything that sounded worse because of it, although I'm just reducing crosstalk, not creating the extreme degree of left right separation that BACCH DSP can. 

@pinthrift

Thanks for the excellent review. If crosstalk reduction were more common, more recordings might be made in a more "hands off" way. As I stated earlier, I’ve not heard BACCH myself, but I’ve used a physical divider, and as you experienced I too heard that less processed recordings tend to do the best, except in the case of purely processed electronic recordings, which can also produce glorious spacious presentations. I think it's interesting that you mentioned "Homeless" in your review. That's been an important track for me as I set up different systems because it should sound amazing with it's rich and dramatic vocal dynamics and harmonizing. I think that track does a good job of revealing problems with listening rooms and speaker placement because it requires clear solid energy in most room's transition zone, where rooms have a way of ruining things. 

@emergingsoul

I think you bring up a good point about most high end stereo equipment manufacturers ignoring the crosstalk issue. Why aren’t more people talking about it? I think a big part of it is that for the longest time there wasn’t any really practical way to address it in many listening scenarios. Recordings were made in two channel format, expected to be played back with a stereo pair of speakers, and the shortcomings were self evident and accepted because, as we all know, it can be very pleasant to listen to, and better than mono.

A similar accepted limitation with most video/film presentation is that we don’t expect it to be in 3D. 3D can add a lot to the visual experience, but it’s a lot of extra effort, and unlike with audio, the crosstalk is visually unbearable so some kind of glasses usually have to be worn if a large audience is to enjoy the effect from various viewing angles. With audio the crosstalk also profoundly reduces the quality, but our mind is more forgiving with audio crosstalk than with visual. Early 3D glasses were of the red/blue lens type, and this obviously had a seriously negative effect on the visual experience despite making it 3D. Similar weirdness can happen when attempting to correct audio crosstalk with crude methods. Now with polarized glasses and other methods it’s possible to get a clear, high quality 3D image with accurate color and very minimal visual artifacts. Similarly DSP can be used with audio now to practically remove the crosstalk artifacts we’re already living with while adding hardly any new audible issues. It’s a huge win.

But you are right - it’s more complicated to set up. More players coming on-board with this type of technology could, in time, make it much easier to implement.

About the quality of your components impacting crosstalk - they don’t. It’s a physical setup problem inherent to using two speakers. It takes some specific processing or a special speaker arrangement such as Polk uses to address it successfully. That said, there are different kinds of crosstalk. What BACCH is addressing is inter-aural crosstalk across your head coming directly from the speakers. This is by far the most severe crosstalk that reduces the overall sound quality, degrading the stereophonic effect, and also introducing severe comb filtering for center panned sounds at each ear, and at frequencies we’re very sensitive to. There’s also room reflection crosstalk, where the sound from the right speaker bounces across the room to the far wall and then enters your left ear. I think BACCH may be able to address these early reflections as well to some degree. There is also crosstalk between channels that can occur in electronic devices. This is generally not much of an audible problem in modern electronics.

@hifidream

I agree that highly directional speakers do certainly help with stereo imaging, but I couldn’t get them to do much in terms of crosstalk elimination. I’m using horn speakers right now in conjunction with crosstalk reduction and I’m getting very good results. I heard some big horns at this summer’s Pacific Audiofest that had the best stereo separation of anything at the show in my opinion. Others mentioned it too. Besides inter-aural crosstalk, early side wall reflections can seriously degrade the stereo presentation too, and it is truly amazing how good a standard 2 speaker system without crosstalk reduction can be at producing a wide, spacious sound field with clear separation between instruments when early reflections are properly addressed, either through directional speakers, room treatments, or a combination of both. With crosstalk reduction it can be even more amazing, but dealing with early reflections remains super important, otherwise the full benefits won’t come through. Horns or other directional speakers can make that easier. I’ve also found that the quality of the speakers and other components remains as important as ever. If the tonality is off or there is too much distortion, the sense of realistic space is severely compromised, although you can almost always still hear some benefit. Even when listening to my laptop speakers I can get some sense of spaciousness with crosstalk reduction that would otherwise not happen at all.