But in the future, after getting more experience, I do plan to do multi track recording myself.
Sorry, I should have been more specific. I do plan to do multi track recording/monitoring, but not for the type of productions you are probably thinking of. I'd do it for training, simple advertising, etc. where the camera can just be fixed or held by a camera operator with very simple instructions. If I get as far as producing films for entertainment, I wouldn't do the sound myself....If your going to direct and do another task (not recommended) it should be shooting. The director needs to SEE the shot and you can't watch and listen at the same time. Your mind will focus on one and usually that will be a visual if you have one. If you are watching the take you will miss things in the sound. Multi track will take all of your attention so that goes doubly.
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Again I will emphasize directing is a full time plus job. You can't successfully direct and do just about anything else. You might be able to squeeze in camera work since it keeps you in the scene but you certainly can't do something that requires you to be out of the moment analyzing what is being recorded. For visualls that backs off a bit doing industrials and docs.
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But even if you are aiming pretty low there should be one person who's sole focus visual, one for sound, and one for performance. If you are shooting with less than that I don't think you can do high quality work in a reasonable amount of time.
Mark, it sounds like you have already sold yourself on what equipment you are going to purchase, and now youre looking for validation on your theory.
is the Tascam well worth the cost? of course it is if you truly will use it and its benefits, will a DR40 do the job you are talking about (industrial education films) just as well? YES
When I originally posted, I was leaning toward the DR-680 but was willing to consider other models as suggested by other posters.
Earlier in the week the free case offer with the DR-680 at B&H photo disappeared, so I looked into the DR-40 and H4N again. That's because that case was what made the unit just portable enough for all of my envisioned uses, and after dropping my idea of ambient recording those both had enough channels.
BUT, it's good I didn't buy either. I found out that there's a good chance I'll be able to do the audio for something that needs the capabilities of the DR-680 (or a mixer plus a 2 or 4 channel recorder). I saw the free case offer was back so I ordered a DR-680 and should be getting it early next week!