Mono recordings are in the DCC standard with double the playtime. Are any prerecorded tapes known to be recorded like this? Maybe recorders with a mono microphone jacks record this way?
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In the past I had used, mono mic on 2nd and 3rd gen recorders, but had no the idea that recording time doubled.
Did you test it your self?
What I do know, that the mic is auto source.
No, I don’t have a microphone on hand and am not sure if it is even recording mono.
I suspect that the dual mono format (aka “4 sectors”) would only be used for things like audiobooks where quality is less important than playing time.
It’s not possible to record 4 sector tapes with consumer recorders. I think the spec explicitly forbids consumer recorders from being able to do it (I’m not sure, I could be wrong), but even if it didn’t, it would be impossible to do especially with 1988-1992 technology but even with 2020 technology.
You would have to be able to record one mono stream first, and then go over the same tape and record the other mono stream without erasing the first stream. And of course if the first stream is shorter than the second stream, the second pass will have to add silence to the first stream. To replace one channel in a two-channel stream would require you to read the old stream first, do all the demodulation, error correction, de-framing of the tape data, followed by detecting and replacing the audio frames, then generate update updated error correction data, modulate the data, re-format the tape etc.
Your recorder may just have a single mono mic input, but it records in 44kHz stereo whenever you use an analog source (mic or line). 4-sector DCC tapes may exist (I imagine there were test tapes that have it) but they could certainly not be recorded with consumer equipment: pre-formatting would be necessary just like with prerecorded stereo tapes.
Not that they’re not interesting of course. I think the dual-mono format is a good starting place if we want to put audio on a DCC tape in a different encoding format e.g. 4 sectors of 192kbps MP3.
===Jac
I think you are right, I did not look into the deepest details before asking. We might achieve it by disconnecting the unused outputs in some way like with an adapter cable between rw-board and head. To be honest, I liked the idea of custom content on DCC in the first place, but now I think we should rather focus on every detail of the DCC standard that it can be played back on standard players.
When I read your first post I thought that double the playtime would mean a halving of the tapespeed. 
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