January 2000

TacT RCS 2.0 Room-Correction System

by Robert Jørgensen

Let me start by telling you that I have known about digital equalization for more than 15 years and have lusted for it for the same length of time. I first heard about it from a colleague of mine who had been developing modems around the time, including a 14k-bit modem that was state of the art and about the size of a monster Krell amp. He was the first person who pointed out to me that a computer could be used for digital signal processing and that this could correct not only frequency aberrations but also phase problems. And whilst he was thinking about stuffing data onto a telephone line, I immediately thought of how neat this would be in my sound system. I think it was only a year or so later that the old AR company announced a prototype. This did work, but it was severely limited due to processing limitations and never made it to market.

Fast-forward to the late ‘90s. What do we find? Modems like the one my friend was working on are such old hat that virtually nobody uses them anymore, DSP has come into our daily lives, and processors excelling at it can be bought for very normal money. In fact, we already find them in tens of everyday products and soon probably more. So finally the raw computing power required has actually become affordable. This was one of the major obstacles for a long time, but need not be anymore.

Another DSP obstacle is the appropriate software. How do you do it so that it sounds right? Just looking at another aspect of the CPU power problem, it is clear that in the past a great deal of effort went into squeezing every bit of power out and this is perhaps to the detriment of the actual processing. Besides AR, also large and well-known B&W made efforts in this area that never made into actual products.

When I mention software as a problem area, it is possible to split this into several concerns. You need to measure the actual response of the speaker. This entails measuring the right things and being able to interpret these correctly for your purposes. You must produce a digital filter on the basis of the measurements. There is more than one way to skin a cat, and this goes for digital filters as well. Just the type of filter you use to implement in the system can make vast differences both in terms of measurements and acoustics. This and the previous point open a true Pandora's Box of options, none of which necessarily leads to simple solutions. Some terms that you run into are IIR (Infinite Impulse Response) filters, FIR (Finite Impulse Response) filters and many other terms that we will save for another time.

Finally, and not by far the least, the software used to set up and "administrate" the filter is of great importance. How user-friendly is it? How deep does the user's technical knowledge have to go to set it up and/or use it? These are concerns that can make or break a product if it aims at the consumer market. (Even though we as audiophiles might not class ourselves as consumers, on some level we are.)

Enter the TacT room-correction system, which by now is not actually something completely new. Huh? Well the RCS 2.0 is a relatively new item, but as systems like these go, they tend to be works in progress. And that is actually pretty good since technology also does not stand still. Not at all.

The TacT RCS is based on work started a good many years ago at Snell. Snell was bought (and later sold again) by the Danish AudioNord Group, which besides running a large distribution/retail chain in Scandinavia also design and produce Dali speakers as well as holding a large percentage of NAD. Over the years a number of attempts and under different names the RCS idea popped up as an NAD RCS and finally under the TacT name, when AudioNord founder and all-round audio visionary Peter Lyngdorf formed this company together with Dr. Radomir Bozovic, who is a scientist with specialty in wave propagation and DSP design.

Having gone down a number of design paths in the past with mixed results, it seems that now TacT has created a design that is not only extremely flexible but also very easy to use. And this last point, in my opinion, is not the least important part of it. As opposed to the RCS 2.2 which included a subwoofer crossover facility, the RCS 2.0 is less robust and much cheaper. On the other hand, it has become quite a lot more sophisticated and user-friendly in other aspects.

Wanting to leave something for a proper review let me merely outline my experiences with the TacT RCS 2.0 below. The first time I had a chance to hear it was at the High End '99 in Frankfurt. In the report from the show I mention that Peter Lyngdorf had some problems with the computer with which he programmed the unit. This limited the different curves available, but the ones he had computed were enough to show that the perception of space and of depth of field was much better with correction in place than when the unit was bypassed. Also solo artists were much better focused, to the extent that it could be quite shocking to turn off the correction.

Some listening at home

Much to my pleasure Peter Lyngdorf was recently in the Benelux, where I reside, and he went out of his way to spend a few hours with me to give me (and my family as it turns out) a quick experience of what the RCS 2.0 has to offer. And that is quite a bit.

After connecting and setting up the microphone and computer, it literally took two minutes to have a correction curve. First the microphone is calibrated with a series of clicks followed by the actual measuring, which again is done via a series of pulses. This speed is a point where the RCS 2.0 differs radically from its predecessors, which could take 45 minutes or longer to do the measuring and calculations for a correction curve.

It is also more flexible in other areas. It actually works in 96kHz/24-bit format. It has five digital inputs and three digital outputs. Furthermore, it sports two substantial hardware options in the form of a set of four analog inputs with level matching as well as an analog output option with both balanced and single-ended outputs. In effect, it can be a full-fledged analog/digital preamp with equalization.

To get back to using it, once you have a measurement, you can overlay an "ideal" curve or more if you want to. The RCS 2.0 will store a total of nine curves, which can be used via the front-panel or the remote, but on the PC you use for the programming you can have an almost infinite number of curves.

First of all, let me say that from the first tones after correction it was obvious that my sometimes-idiosyncratic ribbon-hybrid speakers had become decidedly less dominated by their presence area. They were suddenly much more balanced. Let me go so far as to state that after applying a not very aggressive correction curve to them, they sounded like new speakers. This should only be taken in the most positive way.

On their own, the speakers drop off rather substantially in the treble. This I have known for years. Using the RCS 2.0 we then proceeded to make a number of curves, none of which took up to linearity at the listening position, something which sounds outright awful unless your high-frequency hearing is blasted to kingdom come. In fact, we made three different curves: one that followed the normal treble curve relative closely, another that was increased quite a bit but being about 3dB down at 20kHz, and finally one that was somewhere in the middle. This last one sounded the best on the greatest number of CDs we played whether they were rock, folk, jazz or classical.

To be quite honest, even being aware of the foibles my speakers exhibit, I had not expected the sound to be so much better. The fact remains, of course, that certain laws of nature cannot be circumvented, so it doesn't automatically follow that you can turn any old sow's ear into a brand-new silk purse. All that said and done, I, my wife and my eldest daughter who stayed up with us until midnight playing a great variety of CDs were all impressed. In the few hours we had the RCS 2.0 available, we were not able to identify any weaknesses, but we certainly found any number of improvements.

The RCS 2.0 is -- uniquely so at this time -- very easy and quick to use. I am sure the RCS 2.0 will not solve all possible problems, but I am eager to have a much more in-depth look at what it offers. As the big guy says, "I'll be back."

...Robert Jørgensen
robert@soundstage.com

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