F3
I remember that morse tape - used to do the same thing on a Sunday evening; encoding vehicle licence plates & road signs as I went! Didn't think it was DH's voice on that one though? Certainly his company though - Airtape Publications. Amazing what you actually remember all these years later (haven't got a clue about laser ring gyro's, E/I bar's & logic gates though).
I imagine the development of interactive CBT etc must have rendered audio study a bit redundant. That said, Morse was ideally suited to it in view of how it was tested.