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Frequently Asked Questions
Not yet, but Robin Miller has made many such demonstration recordings and some of them are available in the demo section of this site or at www.filmaker.com A demo DTS 4.0/LPCM/2.0 DVD made by Robin is being duplicated by TacT Audio for shipment with TacT units that operate Ambiophonically.
No. You can rotate, nod, standup, recline and unlike stereo move back and forth on the centerline between the speakers. If you get too close to the speakers you will just hear stereo. If you get too far back the stage may get a bit narrower. If you move to the side you will lose the wide stage, but unlike stereo, you will easily hear both channels no matter how far off center you are. In most stereo systems (as well as 5.1) if you are offside you will localize to one speaker and hear little of the other channel. In a full Ambiophonic system with rear and surround speakers the effect of being off center is like standing up in a concert hall and facing sideways. You are still in a hall you can't localize instruments on the stage but you know where the stage is.
Yes. In most cases, the way one can tell that one is cancelling the most crosstalk is to use the shortest value of delay that results in a stage approaching 180 degrees. Similarly one wants to increase the attenuation starting at say -2.3 dB (decrease the spread factor number 82, in TacT) until the crosstalk cancellation is as good as it can get as evidenced by the stage just reaching 180 degrees or close to this. 100 microseconds or thereabouts is usually a good number to start with. Increasing or decreasing this value is often hard to detect with normal recordings. I would suggest that you use the lowest value that works for your arrangement since higher values can effect the very high frequency response as crosstalk cancellation gradually becomes crosstalk enhancement.
If you over crosstalk cancel then you begin to introduce out of polarity signals that are interpreted by the brain as stage broadening. Thus something that should perhaps be at 45 degrees at the side will seem to come from 70 degrees or even out to 90. In the worst case of over processing some listeners will hear extreme side images slightly behind them. Of course, you can use these delay and attenuation parameters as a form of stage width control.
No. Ambiophonics, like stereophonics, can be listened to using any speakers (but not earphones). Since humans cannot localize at very low frequencies, both the stereophonic loudspeaker triangle and the Ambiodipole perform similarly as far as bass response, room modes, etc. Subwoofer advantages and problems are the same in stereo or Ambio.
The room you see in the picture on the home page is essentially a laboratory. The idea is to have a space large enough and quiet enough that its will not affect any measurements made. Once RACE and the surround ambience programs were perfected it was found that they swamp any normal room reflections. As in a concert hall, the reflections from seats and heads do not change the perception that one is in a hall. Also with the front speakers so close together, one is essentially listening in the near field and the room response is not as large a factor as it is in stereo. In stereo some room reflections have about the same delay as the crosstalk and so change values of ITD and ILD as well as the comb filtering patterns. This is not the case for Ambiophonics however.
The black panels are SoundLab electrostatic speakers, called Surrstats. They are driven by a computer and mimic concert hall walls. If you go up to one and try and hear it directly is no more audible than a side wall in Carnegie Hall.
Ambiophonics and its XTC version in TacT, just eliminate the distortions in interaural time differences and interaural level differences that occur willy-nilly when the stereo triangle is used in reproduction. It is not a decoder. The bottom line is that one can routinely play SQ LPs, Ambisonic UHJ recordings etc. with marvelous results and no decoder is needed for two channel reproduction of these media. Basically all recordings just contain specific amounts of ITD (including your phase effects as well) and ILD. The trick is to deliver these recorded values, stored on discs, to the ears, without compromise at home, and also avoid the worst pinna direction finding errors. For whatever reason, SQ, UHJ, QS, Prologic, and similar matrixed surround recordings play exceedingly well via two speakers and routinely produce stages of 180 degrees. Of course, if you use two Ambiodipoles then you can have the full 360 degrees but only if you feed the two 2.0 decoded signals into the TacT Ambiophonics. The Biggs organ 4.0 SACD is awesome this way and you don't need an SQ decoder. You can also play any 5.1 source this way for a full 360 degrees of direct sound.
The standard LPs, and CDs are not inherently stereophonic. The mics don't know that what they hear will be played back by loudspeakers at 30 degrees that will reduce their ITD by two thirds, limit the stage width to much less than they see, and introduce unpredictable combing etc. If recordings are made with a lot of spot mics they may or may not sound as good as some other recording made a better way but this is true in stereo as well. One reason that LPs sound fantastic in Ambiophonics is that they are purer in a binaural sense. In the early days they could not be panned or mixed to death and thus they often have very high values of ITD and ILD. Some Ambiophonic users do report that they can now hear what the mastering engineer has tinkered with and don't like it.
Ambiophonics enhances the reproduction of any kind of recording, music, video, games, multichannel, etc. But if all you are listening to is a guitar with a vocal soloist, you might as well use one speaker and avoid the crosstalk and combfiltering that two speakers produce. But in the very first article in Stereophile Magazine about Ambiophonics, editor John Atkinson called this methodology "The Domestic Concert Hall". Thus one can make the argument that full bore Ambiophonics with surround speakers suits large scale classical music best, it also enhances jazz and rock concerts not to mention movies, etc.
Normally you would place two speakers behind the listening position for full surround or enhanced 2.0 but if you use side speakers instead of the rears then you just turn XTC off for those outputs. You might also want to pass this side speaker signal through a Prologic decoder so that the sides are only active when there is a strong side signal. The purpose of the sides is to tickle the pinna and make the stage width seem more binaurally natural for the higher frequencies. If the side speaker signal is not coming from the TacT Ambiophonics then you simply need a Y cable from the player, digital or analog, to feed both preamps with the same front signal.
You are correct in that reproduction via the stereo loudspeaker triangle doubles the mid and low bass energy because the sound from both speakers reaches both ears without attenuation. The higher frequencies are diminished because of the head shadow, so normal stereo reproduction actually has a low frequency coloration for central sound sources such as soloists. In Ambiophonics this mid bass boost is eliminated. Thus, in an A-B test, the change in timbre becomes obvious. When XTC becomes correct and the crosstalk is then being really cancelled, the lower region frequency boost due to the crosstalk dissapears and so a mono voice or instrument sounds different. Again, in time, you should hear the stereo version as a distortion and not the other way around. It may be that Ambiophonics can only be appreciated by humans not previously exposed to stereo. Bad habits are hard to correct! Try comparing the Ambiophonic timbre to the timbre from a single speaker to get a valid comparison.
Yes, RACE is not rational until you get down to around 83 or so. This is because the crosstalk cancellation signals are not cancelling crosstalk anywhere near correctly, and thus you are hearing outp-of-phase signals interacting differently at different frequencies. Each human brain will interpret this sound field differently. It is somewhat akin to listening to out-of-phase stereo. If you do this out-of-phase test with the stereo loudspeaker triangle, move around and you will see how things change unpredictably and may remind you of the high spread factor case.