TACT RCS 2.0 Users Group

Comment to Pls1, 031701

Re: Measurement with TacT 2.0 versus MLSSA.

It is absolutely true that the measurement performed and displayed by the 2.0 does not match the response when you measure with other measurement systems. In fact no two measurement systems will concur unless you set all the parameters for the measurements to identical parameters.
When you make in-room measurements there are a number of variables that will influence the measured result:

1. Microphone – is it well calibrated and corrected
2. Gating – how long a window for the measurement
3. What kind of windowing filter, Hamming, Hanning etc.etc
4. What kind of smoothing is applied

The TacT measurement system is designed to be used with the TacT correction system. The measurement uses proprietary frequency dependant gating, windowing filter and smoothing, and the measurement also takes into account the way the sound decays in the room.
It stands to reason that at very low frequencies – where the wavelength is long, it is desirable to correct for all the variation in frequency response imposed by the room while at higher frequencies it can be total nonsense to correct for small variations, simply because the measured results can be completely different if you move the microphone 1”. So the TacT measurement will surely differ a lot from measurements that are designed for steady state response measurements with no regard for what the measurement will be used for.
It fact a lot of the research leading to the TacT Correction systems have gone into the design of a suitable measurement system.
It would have been much easier just to adopt an existing measurement system and use it for correction, and in fact that was what we did in the early trials of RCS, sometimes with reasonable results but more often with rather terrible results.
Re: The comment on number of chips. Yes TacT 2.0 uses 3 very fast 48 Bit DSP’s while the Sigtech uses many more. However the DSP’s used in the Sigtech are ancient designs so it is really irrelevant to compare.

Re: Sigtech versus TacT

In response to comments from a Sigtech owner who have tried the TacT 2.0 without immediate success I would like to explain why the Sigtech owner – initially - is less likely to achieve good results with the TacT 2.0 than other customers.

In no way do we want to belittle the fantastic achievemet made by Sigtech when they brough out their correction system in 1992. However it is important to understand some of the fundamental differences between our products.

The Sigtech approach to correction is to find the speaker position that gives the flattest possible response in the bass region and then apply correction.

The TacT approach to correction is to place the speakers where it is suitable for the utilisation of the living space, and if possible where they produce a lot of bass, and then do correction.

The difference in approach comes from the correction capability of the systems. The Sigtech has a correction resolution of 20 Hz and 50 milliseconds throughout the bandwidth which extends to 20 KHz. The TacT 2.0 has a correction resolution of 2 Hz and 500 milliseconds in the bass region and the correction resolution is then reduced to about 10 Hz in the midrange and further to much less than that at higher frequencies, while the frequency bandwidth extends to 45 KHz.

With the limited resolution of the Sigtech at lower frequencies the correction can not be accurate below 200 Hz. Then one could argue that that is only 1 % of the frequency bandwidth – yes, but that is not how we hear it! 200 Hz and down to 16 Hz is almost 4 octaves – approximately half of the fundamental tones used in music! Furthermore below 200 Hz is where most of the energy is in an average piece of music. Sigtechs´s solution to this problem is to find the position where the speaker system itself will have the best possible frequency response in the region below 250 Hz and then apply correction.

The problem with the Sigtech approach is the following: To achieve a relatively flat response in a listening room in the region below 250 Hz you will have to find a placement of the speakers that randomise the standing waves and pathways of sound from the speaker to the listening position to the greatest possible extent. Unfortunately this also means that the time-coherence is randomised as much as possible. Technically speaking: That the least amount of energy received in the listening position is minimum phase while the greatest amount is non-minimum phase. What is minimum phase and non-minimum phase ? Well it is not so difficult to understand: the signal that has minimum phase in the listening position relative to the speakers own response is the part of the sound that comes directly to the listening position, while the non-minimum phase is the part of the signal that is delayed because it has bounced from a back wall, sidewall etc. ( every time the sound chage direction it also change the phase )
What all of this means is the following: WHEN YOU ACHIEVE A FLAT FREQUENCY RESPONSE BY RANDOMISING STANDING WAVE PATTERNS IN A NORMAL LISTENING ROOM YOU ALSO ACHIEVE THE GREATEST AMOUNT OF SMEARING IN THE TIME-DOMAIN.
So Sigtech can achieve good results in terms of frequency response throughout the bandwidth if you are very careful placing the speakers where the inherent response is flat already at low frequencies – but the penalty can be a lack of time coherence in the fundamental range of music.

Once the speakers have been placed for flat response – meaning least amount of minimum phase from the speakers / greatest amount of time smear – then the options for correction is limited. Why is that ? Simply because no correction system – even theoretically – can change the way the low frequencies radiate from a speaker box. (without putting DSP power on each drive separately). So once time coherence is lost it can not be re-established.

With TacT correction systems we encourage to experiment a little with speaker placement as well. But now with the intent to find a position of the speakers relative to the listening position that yields the greatest amount of energy from the speakers and then apply correction. That usually means placing the speakers closer to the back wall, and closer to the corners. Yes, that will increase the bass level – but what does that mean ? It means that a greater amount of sound travels directly to the listening position without delay and phase shift, so the time coherence is better. Obviously the frequency response is much worse but that is easily corrected with the TacT system. (The TacT operates with 48 bit internal resolution so any amount of correction can be performed without noise or distortion).
So with the TacT correction units you have the ability to achieve both a good frequency response and a good time coherence. Once you have heard what that does to the palpability to the music you will have little doubt that we are barking up the right tree !

Peter Lyngdorf , TacT Audio.

Mr Lyngdorf is incorrect.

I have both units and have long term experience in this area.

Fact: With the Tact you have no way of knowing what the end result is after correction. When looking at the actual measurements after correction using industry standard mesurement tools (MLSSA, it will be clearly demonstrated that the end result does NOT look like the target curve. Transalated--you are guessing when you pick a target curve.

Doing the exact same thing with the SigTech, you get what you expect---that is, if you tell the SigTech you want a flat response, you get a flat response (that is flat in the sense that the FFT of the time domain is flat).

In addition, the SigTech does NOT require that you place the speakers where you get the flattest bass response. While there may be some benefits to that approach, I can assure you that most of the SigTech installs I am familiar with (hundred of them) have the speakers where, in no particualr order (a)they fit within the rooms decor (b) the optimization between bass response and image depth (usually determined by the distance from the front wall) is considered and (c) customers personal placement preference.

On a more subjective basis, Mr Lyngdorf's comments notwithstanding, I could argue that the bass correction of the Tact sounds worse that the SigTech. I can demonstrate that from about 300Hz up the SigTech give MUCH BETTER response.

All of that said, I would summarize as follows: (a) for a fully function digital preamp with a good D to A converter and the ability to do your own room correction, you pay about $3500. The equivalnet (almost) SigTech (new) cost 3 times that (b) with some care (and some external measurement software) you can get much better sound (MUCH, MUCH, MUCH BETTER)with the Tact than you will EVER get with out one in 98% of the rooms.

While I can (and will) argue that the SigTech is the superior product in terms of sound quality, the Tact beats the pants off of no room correction and in terms of dollars per unit of sonic gain, the Tact wins against the SigTech.
If you can afford a SigTech, get one. If you can't, run, don't walk to your local Tact dealer.

Audioguy123, can you give a general description of the TacT's variation from target correction (which frequencies, how much, etc.) in your experience of measuring it? Thanks.

Drubin--it is not consistent. The one place where it is consistent is in the low end. If you use one of the curves with the boosted base, you actually get flatter base but the problem (as I stated in an ealier post) is that you don't know how much to boost the bass in the target curve (and what slopes to use) to get the correct flat response.

Sorry I can't be more help. There is some stand alone software that you can use with a Tact that by an iterative process you can get the desired result. Try www.ETFacoustics.com.