Audio commentrary

Just reading Nicola Durbridge's contribution to Bates' 'The Role of Technology in Distance Education' published way back in 1984 I think. This is the era of the audio cassette and the chapter reflects on why it was useful for UK Open University teachers.
Durbridge first discusses audio, appreciating how modulation of the teacher's voice distinguishes audio from the written text. She then discusses the cassette in terms that will be familiar to those interested in mobile learning.
At this time there was no Internet and so the cassette provided an important contact point for distant learners, connecting them to their teachers between their infrequent meetings.
The use of audio commentary is a method described here and one that I believe is still valuable. In the age of the DVD, where films come with bonus layers of commentary, it is surprising that more is not done by academics or students in creating commentary recordings on texts and situations. The use of audio feedback, as a type of commentary on student assignments, is used. However, much more use of audio, the MP3 recorder and it's pause button, could be made. Commentaries or reviews of academic texts by academics is an obvious way of encouraging student engagement with key texts. Student commentaries, that might be compared, on readings is also a simple technique to implement.
Is anyone using such techniques?