Funny,...
but the mixer section of the 464 and 564 are virtually identical.
A significant difference between the 464 and 564 is that the 464 runs on easy-to-find, economical cassette tapes, and the 564 requires hard-to-find, pricey MD-Data discs. Average: $2/cassette vs. $15/MD-Data disc.
Another significant difference is the 464 has simple locate, punch in/out editing facilities, and the 564 has whizbang non-linear digital locate and cut/copy/paste editing, plus "bounce forward", (already mentioned, but worth mentioning again). More, the 564 has "virtual" track capability, allowing for 5 alternate takes to be stored, before choosing one.
The 464 has a digital, menu-driven 4-buss assign matrix, while the 564 has a somewhat simpler switch-driven 2-buss assign PLUS 4-direct capability. The 4-buss design is somewhat higher function than the 2-buss + 4-direct design.
The 464 has LCD Level Meter "bars" integrated into the single LCD display. The 564 has a dedicated LCD function display PLUS 4-(separate)-LED Meter "bars". HINT: the LED Meter "bars" are much more highly visible.
The 464 and 564 will both record 4-tracks simultaneously,... 4-total.
BOTH the 464 and 564 are simple removable media devices, which simplifies archiving of "data", considerably.
The 464 and 564 actually share many common design features, depite being quite different, too. (Is that a contradiction?) They are both roughly the same size.
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The 788 is an entirely different design scheme than the 464 and 564, that all bets are off. The 788 has an entirely LCD menu-driven environment, with a minimum of knobs & buttons that perform multi-functions, depending on what menu you're in at the time.
The 788 has all the latest Cut/Copy/Paste, non-linear digital editing capability, LOADS of "virtual" tracks, and 999 levels of "Undo",... features not matched by either the 464 or 564.
The 788 is a fixed media device, which requires a specialized and dedicated additional CDR burner accessory, for any true "archival" functions, beyond the simple "mixdown-and-dump" scenario.
The 788 will record 6-tracks, simultaneously, & 8-total. The 788 is smaller than either the 464 or 564.
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(these days) Everyone pretty much "assumes" the 788, being digital, would have the "best" sound quality, but that's NOT borne out in the specs. By specs alone, the 464 and 564 probably sound "better", although there's no denying that the satisfying "fat" sound people are usually looking for comes from the 464, & analog tape.
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Conclusion:
A) If you have the bread & the price is right, get all 3!
B) If you have enough bread to get 2, get the 464 and 564.
C) If you're limited by budget, in the long run you'd be better with the 464, alone, based on cost of cassette media, saving you a lot of money, especially if you're more prolific than not.
I'd not necessarily recommend the 788 by itself, on any of it's merits alone, OTHER THAN IT's A FULL 8-TRACKS. THE OTHERS ARE 4-TRACKS. However, the 564 has "bounce-forward" that bridges the gap, somewhat, AND, if by chance you had BOTH the 464 AND 564, you could get into some pretty sophisticated bouncing schemes, bringing the utility of the 4-tracker a bit closer to that of the 8-tracker.
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That's my SHORT answer.
