Digital Room Correction: The Final Frontier?

The TACT is a very powerful tool and is capable of producing wonderful results. On the downside it's only appropriate for digital only systems and the software is complex with skimpy documentation. I've been using a TACT for about a year with very positive results. You still need to pay careful attention to speaker placement and room treatments, but the measurement capabilities of the TACT bring some rigor to the process. I recommend removing all room treatments and then adding them back one at a time and measuring. Also the system is very sensitive to the microphone's orientation and placement during the measurment stage.

Their is a TACT user group that you might find useful.

Of course, it's good when we don't have to correct rooms electrically but can do it passively--this can be almost impossible in the bass region. I'm not at all surprised as to your findings--I only wish you had found our company first. We are an acoustical engineering company that designs listening rooms, but recognized this issue and we were not satisified with any of the devices on the market. We make a PARC device designed specifically to deal with the bass mode problems. When we designed it I was very concerned about signal purity and having a degree and graduate work in digital signal processing I knew that I wanted to stay in the analog domain. Part of this was due to my love for vinyl and upcoming formats that might be degraded in the digital domain, but part of it was just a characteristic nature of running the signal back through an A/D and D/A converter. So we designed a 3 band parametric notch filter system that has a range of 16 to 350 Hz, Q factors of 1 to 11, and attenuation up to 18 db. I don't think any other unit has anywhere close to that head room. It's digitally controlled but the audio signal remains solely in the analog domain. The unit is calibrated using proprietary software that has a psycho acoustical response filter (it reacts similarly to the human ear in terms of gating times at different frequencies.) You can also calibrate the unit in a manual method with test tones, but this is more time consuming and not as accurate. It also doesn't have the advantage of being able to see the graphed results in near real time.

The other thing that is very interesting is that you have Talon speakers. We used the PARC at CES on a pair of Talon's new Firebird speakers. Mike Farnsworth, president of Talon, was delighted with the sound and told me he wants the PARC at all shows. He had not been happy with any other correction system he had tried in the past. We will be with Talon again at HE 2003. For more info on the PARC.

Obviously, I'm clearly biased here. I do believe we designed an incredible product that sounds better than anything else that corrects for room modes, with excellent build quality using connectors like WBT and Neutrik. But perhaps more impressive was making this device at a more affordable level.

Rives, In the past your posts seemed to be helpful and responsive to inquiries. In this case it seems that its just advertising and meant as much for the consumption of other readers as for the original poster. It appears from the posters comments that he has little understanding of standing waves caused by room dimensions and how one can avoid them passively, or at least lessen them substantially. You could at least have referred him to your web site wherein you have a good discussion about the problem and provide evaluative tools for proper placement of speakers and listening positions (at least for starting points). Incidentially, after I looked at your site, i checked my speakers and they were within 1" of your suggested location - the listening position was not as close.

Newbee--was that on the simulator you are referring to? It does a pretty good job and is really designed to flatten the frequencies as much as possible below 500 Hz. Above that number you may have notice very little changes. As to your other comments, I appreciate those and was worried about that a little. I should have pointed out the listening room, which is a tutorial and describes more about bass modes and also has a simultor (which is what I think you were referring to on the speaker and listener placement issue).

Anyway, I do want people to know about the product we've developed--and I think my enthusiasm for what we've done didn't really come across as such--but as you said more advertising. That was not the intent, but I certainly understand your point.

Rives,
Does your product address time alignment issues ala Tact? How do you avoid injecting phase incoherence when performing analog eq? I, too, have been eying the Tact systems, however, they are expensive, and I am not looking to add another D/A or A/D in the signal chain.

Rives, from what you are saying, your product would work with DVD-A and SACD formats as well as vinyl (while the TACT would not)--true?

Duddley:
The PARC is designed to do one thing and one thing only--deal with room modes. We wanted to keep everything in the signal path as simple as possible (but not simplier). Thus, we do not address time alignment issues, nor do we operate on the full audio bandwidth--bass only. There are two areas that one might want to apply time alignment to. One is a poorly designed speaker that requires additional processing, and quite honestly most high quality speakers now are designed with cross-over and drivers that do not have this problem. The other occurs from room interactions and is far too great for any device to deal with properly. Even if it could, it could only do it for one very specific spot in the room. TacT will admit that the time alignment issue is not terribly relevant, but since the data is in the digital domain, and they have to do some time alignment to compensate for the digital convolution filters, why not allow the user to adjust it as well.

How do we avoid injecting phase incoherence in analog? Quite simply we don't. It's impossible and is the laws of the type of electrical circuit necessary to do parametric equalization. It's a direct function of the Q (width) and attenuation. There are two types of phase distortion that can be caused. One is cascading and one is indepedent. We use an independent designed filter. The phase shift is maximum at the center pole but is not changed outside of the bandwidth. Initially this was a big concern of mine, but after extensive listening and testing on very high resolution systems we discovered that we could not detect phase shifting with notch filters (attenuation only). We could detect the phase shift when the Q was relatively narrow (greater than 4) and the boost was greater than 6 db. The PARC is to deal with room modes only and thus does not allow for a boost, only attentuation.

Calanctus: That's not quite right. The TacT can work with these formats, but it's going to take their analog outputs (not native digital format), then run them through an A/D, then process the new digital signal, then another D/A. So you can do it, but it's very convoluted and not a very pure way of dealing with these high resolution formats, you will lose much of the detail and ambience of these higher resolution formats with the additional conversion and processing.

In either case--hearing is believing. Please do take time to listen to a unit, whether it's an in home audition (best) or at a dealer or at HE 2003.

With an A-to-D converter option, the TacT units WILL
work with vinyl. I'm using my vinyl system that way.
And, it works beautifully. I've got Magnepan 1.6QR
speakers, and I use Room Lens clones behind them for
greater diffusion, but the TacT RCS 2.0 is an enormous
improvement in the musicality of the system.