I’ll point out that a common method of detecting bugs at the time was to set up a radio receiver with a speaker and then sweep the frequency, if you managed to hit you would get a feedback sound between the speaker and bug. These oddball modulation schemes would prevent that from working.

I like it a lot that many of techniques have a hybrid analog/digital structure that would involved sample-and-hold, sweeps and comparators like the Triple Pulse scheme.

Today I can’t believe you wouldn’t use some digital solution but at that point in time you’d be lucky to be able to use a small IC.

Today with spread spectrum, it's probably much easier to hide a covert radio signal.

In practice most audio channels are low-pass filtered and bandwidth limited, so I'm guessing that these modulation techniques are not going to work. Also, we have digital methods now.