Subliminal music exists for almost any purpose, including advertisement, theft prevention in department stores, fitness, healthy eating, relaxation and even medical rehabilitation. The first step to creating your own subliminal music is to decide on the message you wish to embed within the music. If you're trying to lose weight, include a message such as "I want to eat healthy food." To stop smoking, use "Smoking kills."
Most subliminal music is of a nature that people will find pleasant to listen to. Relaxation music is a huge industry and uses sounds from nature, such as waves, dripping water or animal sounds. If the music is soothing and pleasant, the listener's mind may open up and be more receptive to hidden messages buried within. You can create subliminal music using any style of music. The music is simply the carrier for the message.
Digital audio processing allows anyone with sound-editing software to manipulate the human voice in countless ways. Known techniques include the speeding up and slowing down of a voice, whispering and otherwise altering the sound of the voice. Cloaking the voice is also possible by synthesizing it or combining it with another sound. The best way to approach it is to alter and record. Experiment by recording various versions of the message(s) using different effects and techniques.
The music should be on one track, and your altered voice on another. Volume is a critical component of this process. Too much volume will expose the message and defeat the purpose. Too little volume will reduce or eliminate the subconscious mind's ability to pick it up. Try adjusting the volume until you can hardly hear it and then turning it a little lower so that it's virtually inaudible, for example.
Mixing in your various versions of altered-voice messages must be rendered and tested. This is not an exact science, so that it may take some time to achieve any noticeable results. Record some of your subliminal music, and play it for other people. Tailor your message to suit a particular person's needs to see if it has a positive effect over time.