Hi Kirk
I know this is controversial and the good fellas over at Shadow Vector would respectfully disagree with me but I made a deliberate decision way back in the pondering years to restrict it to 3 bands. Yes it would help in yielding more spectacular separation NUMBERS but as I have said repeatedly we have never chased the numbers but focused on the sound and things like image smear , pumping and gurgling.
I spent a lot of time looking at the spectra of lots of musical instruments, human voice etc and was very conscious that chopping up the frequency into too many bands could smear the harmonics of the instruments- with the fundamental going one way and the harmonics going the other way. On all reviews I have read a consistent comment is that we tend to move objects as a lump, not in bits. To me 3 bands was optimal.
Certainly with multi-band surround sound decoding there must be a point of diminishing returns. Itās hard for me to visualize the SM sounding any better with twice as many frequency decoding bands. In fact I think the case can be made that tri-band decoding is over kill. Hereās why.
Start with the bass. Traditionally lower frequencies were always mixed equal left/right in stereo records. This was to reach a desired bass play back output that didnāt over drive the mechanics of the cutter or play back cartridge. Today in digital you can do what ever you want but still itās usually mixed the same way as two woofers are better than in playback to reach a desired bass SPL.
In a QS/Involve decoder that means the bass is basically center front. I posit that a simple RM/QS non-enhanced decoder circuit would work just fine for the bass. Thereās a fine point not frequently discussed that when you derive a directional control signal from audio input, it starts out as an AC signal & ends up a DC control signal. Rectified it is like a power supplyā¦ it has ripple that must be smoothed out or it will impose IMD on the following gain control circuit. So basically a filter cap is added to smooth it out.
Hereās where all that talk about how smooth/fast/slow in decoding action comes about. The lower the frequency the more filtering you need. In a single band decoder itās quite the compromise all tho thereās variable attack/decay ways to work around this. In a multi-band decoder you can use larger filtering time constants for the low frequencies, and less for the mid & treble. Using a basic decoder for just the bass gets around all of this, the sound would simply ābe thereā. Whether itās mixed to come out a single or a pair of speakers, when decoded it would always get the intended direction right, just within the limitations of a simple decoder.
As for the higher frequencies that would definitely benefit from separation enhancement. Again tho, I donāt think you need to split mid-range from treble. Most fundamental frequencies in music are mid-bass to upper mid-range. It seems over the centuries musical instruments have been designed to be easy to hear and often to accompany the range of the human voice. There are several types of flutes out there & we think of this as a high pitched instrument but really the fundamental range is not that extreme & any higher frequencies will be harmonics. The direction of the harmonics will be the same as the main note when recorded/reproduced. So splitting the mid & treble up is of dubious benefit to me. I used a flute as one example but again most instruments have the power in the mid-range and any upper harmonics I can not visualize coming from a significantly different direction that it needs to be individually decoded & enhanced.
There are of course exceptions to what Iāve said. Midiās & synths could have a huge octave range & modern mixing could put any note any where in the soundfield. And in one Enoch Light LP I have thereās a strong double bass fiddle center front with a rather loud triangle from right back. Itās this kind of a situation that multi-band surround sound decoding really shines. Even with this example using only two bands would suffice & give equal results.
So really, after all these years of listening & pondering and even building my own two band Vario-Matrix decoder Iāve come to the conclusion using a simple non-enhanced decoder for the bass, and enhanced high separation decoding in a single band for the higher frequencies is the perfect balance between circuit simplicity & decoding quality.
Most interested to hear your point of view on this, Chucky & others.