TACT RCS 2.0 Users Group

Has anyone compared other Analog to Digital converters with the Tact on-board unit, e.g. Wadia 150 or dCS? I just bought a unit with the ADC, but want to know if it would be worth upgrading to an outboard ADC since I'll be feeding in a pretty good analog front end.

As per above, I compared the Tact to outboard DAC's and it isn't as good. The digital volume control is best over a limited range. I use a shunt to ground volume control in my monoblocks to allow for setting the output from the digital volume control in the Z-Systems (which has a better digital volume control than the Tact) to its best range.

My question was about ADC not DAC. Thanks.

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.