[sdiy] vocoder ancient history

[Henry]

I believe the first vocoder was patented by Bell labs in 1935 and adapted
for so that Churchill and Roosevelt could have secure /voice/ communications
across the atlantic on an HF radio link.  The voice bit rate needed to be
reduced to 300Hz so that two identical one-use-only 78 rpm discs of recorded
noise could be used at either end for synchronous encoding and decoding.
The discs were broken after use.  Many banks of valve units were required.
This is mentioned in a book by Andrew Hodges about Alan Turing and his
involvement with such things.

Henry.