^ That's the way to do it. It's just that lining them up and stretching are post processing tasks dyneq enjoys least (I relate and often don't actually get around to doing the post processing on my recordings).
The "less than open" recording end hassles are mostly about doubling the wiring, connections, batteries, SDcards, making sure both decks are set the same, operating correctly and that both are recording.
In the past, I looked around for a passive, 3-channel mixer with 1/8" jacks like the Rolls MX41b. I can't imagine trying to get that + battery box + lots of cables working for me when running less than open. And, I'd have to nail the mix live vs. post-processing flexibility.
Do you have any samples of this technique that you'd be willing to share?
Yeah, these days, other than dedicating one channel of a 4ch recorder to a SBD feed, 3-mic configs probably make the most sense for SoundDevices Mixpre3 users who only have 3 mic inputs. Other than that it would be folks with 3 channel preamps or mixers feeding 2ch recorders, but there is too much variation to guess on a good mix without listening
You might keep an eye out for a used Tascam DR2d (unfortunately discontinued, with no direct replacement), which is PCM M-10 sized yet can record 4 channels of external input simultaneously via its seperate Mic and Line 1/8" TRS mini jack inputs. Then you only need 2 battery boxes to power the mics, maybe even just one battery box if the PIP over the Mic input is sufficient. That significantly cuts down on the recording end hassles, plus the two resulting stereo files are fully aligned and clock sync'd. You still need to open them in an editor to mix them, adjusting level balance as appropriate between the two pairs at a bare minimum, but that's doesn't involve much more than editing a straight 2-channel recording, and hearing it come together as you adjust the balance between the two pairs is the fun part IMO. Thats really the minimum amount of post processing you'd need to do with
any 4 channel recording.. so if that's a deal-breaker, its probably best to stick with 2 mics > 2 channels. Plenty of ways to chase that dragon without ever moving beyond 2 channels.
I think there are 3-channel samples from other users posted in the OMT threads, but can't say how far back. I don't have a sample of this easily available myself currently, but will look to see what I can dig up.
And in that vein, I've long been meaning to put together a few sample sets of my own OMT recordings so that tapers curious about OMT can hear the progression as additional channels are added and hopefully get a feel and better understanding of what OMT is all about and intended to achieve. Samples would be provided fully level balanced and processed as they would be in the final mix, yet available as various combinations, illustrating the sonic progression as the additional channels are added. I'd also make them available as individual pairs so that folks can listen to them in isolation and in various combinations without having to make any leveling and balance choices.. just pull them up and play them. Maybe I'll make it a New Year's resolution.
As example, one song from an 8 channel OMT recording, made available for easy comparison as:
2ch- Spaced omni pair alone
3ch- Forward-facing center mic added (omnis + single center mic)
4ch- Side fig-8 added to that (omnis + coincident pair)
5 or 6ch- Addition of Rear-facing mic(s) (single or pair)
7 or 8ch- Addition of near-spaced supercards (side-facing or 45° forward angled)