Extracting a center channel from stereo sources is something I have done quite a bit of. The majority of stereo music songs in feature films, music which is not original score composed specifically for the film, is matrixed to three channels so that all three front stage speakers are reproducing the song. I've done it a zillion times on films I've worked on, and know quite a bit about doing it.
And the result is always the same; the imaging suffers. This is not because I don't know what I'm doing, or are stupid, but merely because of the limitations of matrixing which cannot be avoided. Not even by the kid genius who makes this Trinaural gizmo.
Extracting a center channel from a two channel source works very much like the "Dolby 3" matrix on some home theater processors. The success of all these processes is very much dependent on the program material; popular music with a very strong phantom center channel devoted to a vocal has more success, but the left-center and right-center imaging is still far inferior after the matrixing process than straight stereo.
Music recorded with more natural microphone techniques such as classical has its imaging totally destroyed by matrixing processes.
The core problem is that all of these processes must decide what is going to be routed to the center speaker, and it has a lateral "window" in which it must either re-route the signal to the center, or leave it as-is. Take a classical piece where a flute soloist is perhaps 5 degrees right-of-center. Matrix systems will capture this signal (and all the other instruments around it) and route it through the new center channel. Obviously, that flute is no longer in its proper imaging spot, and the imaging outside of the center channel changes dynamically depending on who is playing what notes at the time. The "window" can be either wider or narrower, but it must exist, and by virtue of the fact that there is a window at all, some signals are not going to be where they were when the recording was made.
Matrixing destroys the subtle imaging in the two areas from left to center and right to center. Worst of all, some signals which are on the "edges" of this window, and have subtle harmonic structure (such as violins) will dance back and forth between the center speaker and their original position depending on the notes being played. The result is very ugly sounding.
Of course, the inventor of this Trinaural processor will strongly disagree and spit out nonsensical verbage in defense of his toy, but the bottom line is that he is making money from this thing, and would be the last person on the planet to admit that his baby is ugly.
As a bit of history, three channel stereo is not new, and the name "Trinaural" also dates from the early 1950s. As early as the 1930s, Bell Laboratories studied the problem of multi channel audio and concluded that for proper presentation, 3 channels were required. When Leopold Stokowski made his historic stereo demonstration with the Philadelphia Orchestra, it was done with three channels, left,center, and right.
After World War II, there were essentially two variations of "stereo". The name "stereo" was reserved for 3 channel systems, and "binaural" was reserved for 2 channel listening using headphones (and sometimes speakers). In the early 1950s, Ampex introduced their 300-3 mastering magnetic tape recorder, which recorded 3 channels on 1/2" tape (also during this period Les Paul was on the fringe with his 8 track 1" tape machine, also made by Ampex, but its use was confined to his use only). Almost all commercial recording in America was done with these 3 channel Ampex machines. In the classical music area, recordings were made using 3 microphones for basic pickup and these were routed to left, center and right channels. You can buy these recordings in their native 3 channel presentation on SACDs from original recordings made by RCA, Mercury Living Presence and a few others, and hear them as they were originally intended. And yes, "Kind of Blue" was originally recorded on 3 channel 1/2" tape.
In the popular music area, two of the tracks on the Ampex were devoted to 2 channel stereo instrumental material, and the third channel was used for the vocals; this was a primitive form of what would become multi-tracking on 4, 8, 16, 24, and up to 40 channel recording (Stephens Electronics made the 40 channel recorders using 2" wide tape - they also made a 32 track machine). The 3 channel master was then mixed down to traditional 2 channel stereo. This procedure lasted up into the early 1960s, when 4 channel tape was introduced.
In the early 1950s, Hi-Fi hobbyists could buy 2 channel stereo tapes, most of which were mixdowns from original 3 channel master recordings. Native 3 channel tapes were never introduced because it would have been prohibitively expensive to do so.
In the latter part of 1957, Audio Fidelity introduced the first 2 channel stereo record using the new Westrex 45/45 cutting process. This made it possible for the masses to hear "stereo" in their homes.
The 3 channel masters of all the recordings made during the 1950s and 1960s were never heard in their native format by the public until SACD made it possible to hear them as they were originally recorded.
With modern speakers and electronics, it has become unnecessary to use 3 channels to hear "stereo"; the phantom center channel present in recordings offers imaging as good as that from discrete 3 channel presentations, at least for those in the "sweet spot" between the speakers. And lets face it, anybody who is concerned enough about the presentation and imaging of their music will always be seated in that "sweet spot".
