A thousand apologies for being so tardy with this: I've been running around trying to get to grips with my new job, but I'm now in a position to start if it is not too late.
Below are a few points that have occurred to me. They relate to my context of teaching 'English as a Foreign Language' to international students on a Foundation programme.
First of all, because one of our aims is to improve the level of language knowledge and skills, with written assignments we usually show some of the main erros we find as well as comment on the content. This is not correction, but an indication of the types of error, so that the students have to think for themselves in order to correct their own work. This would be far too tedious to attempt in a spoken format, as it would be so difficult indicating which line of which paragraph the problem was in and so on. So we will continue to need to give a form of written annotation as well as audio. On the face of it, this might suggest duplication, although in reality adio feedback will be additional feedback such that we don't normally give - perhaps a sentence or two only is the norm. However, the potential benefits are great, so I'm keen to give it a go.
The second issue is that our students are doing a wide range of assignments, from group presentations, webquests, online listening to the more traditional grammar tests and written essays (the latter mostly not very long). Typically, they have two or three short assignments each week, as well as longer pieces for the end of semester. Feedback is therefore regular and quite varied. I did a trial run with MP3 files after a recent speaking test, and needed help to sort out the technical issues. Once I'd got the hang of it though, it was relatively straightforward. We'll see if I remember what to do next time. But with so many pieces of work coming in all the time, I'm concerned about the implications for time of doing additional recordings.
Finally, for now, there is the question of how much some of the students understand spoken rather than written feedback. I can imagine certain students thinking 'what did she say?' With no written word there is not the same option to check in the dictionary, especially when you have no idea how to spell a spoken word. This suggests the need for regular dialogue with the students as to how they are finding oral feedback, with further impications for time ... aaaaggghhh!
Anyway, as I said, I'm still keen to give it a go, so let me know if I'm too late or not.