SMPTE is a timecode which is used to sync Tape machines with other tape machines , or Tape machines with computers etc.
When we record analog we keep 1 channel where we call it SMPTE.
So as you'd imagine SMPTE actually has a sound.
This is how it sounds like
So what's described in the handbook is the following procedure.
Take 2 Console channels (1st has the voice)
Take a SMPTE Code generator and put it to the 2nd channel.
Gate the channel with the running code so you hear nothing.(Set the gate to EXTERNAL or EXT KEY)
Use the vocal track as KEY to the Gate and set the Threshold so as it opens and closes with the voice. (side-chain style). This will let the SMPTE Code be heard only when the voice "exists" in the mix.
Then you have 2 signals playing together , the Flanged vocals , and the SMPTE Code , well simply mix them!
Old recording/mixing books are FULL of tricks, i've read and put to test most of them.
This here shows a point where studio gear exploitation meets creativity.
For 99% of the studios SMPTE Code was just a machine.Here it's used as an effect! Great stuff!