TACT RCS 2.0 Users Group

I have had a Tact 2.0 for about 6 months. All told, it has been a wonderful addition to my system. I can't bear to listen the system without the Tact running (and I thought my system sounded great BEFORE the Tact). The associated computer software for the Tact leaves much to be desired -- it's not even friendly to engineers such as myself with training in digital signal processing. I also wish that it were possible to do a post-compensation check of the equalized response. I also wish that the output format allowed for 24/96 given a 16/44.1 input... the scaling applied to the compensation filters appears to be overly conservative and can cause several bits of resolution loss (the scaling is why one has to back off the gain of the "bypassed" signal in order to level match a compensation channel with a bypassed channel). All in all, I think it's a breakthrough product for $3K, and it is real and here today, as opposed to other perpetually promised technologies. The other piece of hope is that Tact continues to refine the product through additional software releases. The application software running in the Tact box is downloadable from the PC that runs the compensation filter, so there may be potential for continued product improvement. Sure wish they'd fix their web site though...

Concerning speaker placement with the Tact... I also tried following their advice concerning moving the speakers towards the back wall for increased room coupling. I have full-range reflex-loaded speakers (PSB Stratus Gold-i), and found that getting close to the wall is counterproductive: even after compensation by the Tact there's too much residual room boom. (The configuration of my room doesn't permit me to go wider with the speakers, so I can't comment on that). I've found I obtain the best result by starting with speakers in the position that gives the best sound *unprocessed*, and then using the Tact to do the room compensation.

Question 1: I found the TactG1 best suited my taste in terms of the provided target curves. I have a PSB Stratus Gold-i speakers (full range). Other curves would work better for speakers with a more restricted LF response.

Question 2: TactG1 was a good starting place, but what I'm running now is a hybrid of TactG1 and TactF1 (I spliced the HF portion of TactF1 in place of the highend of TactG1), and I tweaked the midrange (500 -1500 Hz) up a bit, with a max rise of about 1 dB at 1 kHz for a bit more presence, and boosted the upper bass / low midrange a a skoche for a tad more warmth and bass oomph. I find the Tact curves just a little too dry (I add ed 0 dB boost at 250 Hz rising to about 2 dB boost at 100 Hz, then smoothly sloping to match target curve at around 50 Hz). I'd be happy to e-mail my target curve to anyone who's interested.

Question 3: Get the house as quiet as possible. I wait until everyone's gone to bed (although St. Bernards snoring in the mudroom carry a long way), turn off the central heat, and wait 'til the refrigerator stops running. Turn up the preamp volume to a LOUD listening level, and use a lot of averaging (I use 20 averages, but 100 would be better -- an effective SNR increase of 7 dB in the measurement).

Question 4: tweak and listen. An experiment I'd like to do is to program a Fletcher-Munson equal loudness curve as a target curve. See, for example,
http://www.sfu.ca/sca/Manuals/ZAAPf/e/equal_loud_cont.html The curve describes the relative power level needed for a sound at any frequency to sound as loud as a
reference tone at 1 kHz. In effective, it's an equalization curve for the "typical" human ear. It shows that at moderate levels (say 80 dB SPL at 1 kHz) significant
boost and buck (a few dB to over 10 dB) of various frequencies is needed for those frequencies to sound as loud as the reference 1 kHz tone. So even though the target
curve is decidely unflat, using this target should result in a systems that SOUNDS flat. By the way, see the Stereophile archives for J. Gordon Holt's article on why "Flat is Bad" (or similar such title).

Question 4, cont'd -- I'm also suspicious that the Tact inverts polarity (am running in DD mode)... I found that with the Tact in the signal chain, my systems sounds a bit more open if I switch on polarity inversion in my preamp (this effect passed the "honey, do you hear this?" A/B blind test). I suppose what I ought to do next time I calibrate is turn polarity inversion on, calibrate, and then turn polarity inversion off and run the system that way as a matter of course.

Question 5: I remeasure every time the room configuration changes. I've found that once I've calibrated the room, even relatively small changes are audible degradations
in sound quality -- a large pile of books on the coffee table for example changes things noticeably. I've changes some components ranging from cables to preamps and not
recalibrated. If these components do not have flat frequency response, then any sonic impact they provide will be (or should be) washed out the next time I recalibrate.

Does anyone have any info concerning future product upgrades to the Tact 2.0? Wonder how Tact is doing as a company, between their, um, modest website and low-key advertising, I'm wondering if they're going to lose the high ground to other companies (such as Perpetural Technologies) that do a much better job at promoting, yet don't (yet) have the goods to deliver.

Drubin, quite right about the F-M curves being indexed by reference SPL level... you'd have to program a set of target curves (no problem-o with TacT's 9 EQ memories). I think what happens in real life is that room gain gives the bass boost which is a key feature of the F-M curve... so even a speaker that measures flat anechoically will approximate a F-M curve. I think a lot of what goes on with system matching (including cable-ology) is an indirect attempt to equalize the system frequency response (to an actual F-M curve? actually, to the actual response of thatindividual's ear)

As far as volume level goes, it affects the SNR of the calibration measurement, so higher volume is better from that standpoint. On the other hand, I could see that loud pulses could start driving an amp and speaker into dynamic compression, which would alter the measured frequency response (the amplitude-compressed pulse would have differenct spectral content than the assumed spectral content of the digitally generated reference pulse). I haven't experimented with this issue; I simply set my preamp gain to what corresponds to a fairly loud listening level.