Most effective sub-audible techniques?

[veezee]

What is the best way of altering the audio used in audible subliminals, where you can vaguely hear speech in the background?

Do you find compression, reversing or something else to be most effective? I have a couple of files I'm trying to put together and am working on making the affirmations as effective as possible through different disguise mechanisms and through trying different grammar and sentence length.