Is it possible to use steganography using an analog audio channel?
I know this can be done using images. My idea is to encode an audio message in way that if listened by an ordinary device (e.g., radio or telephone) it delivers a normal message. But if we use a special decoder, the receiver can listen to a hidden message. Please note that I am interested in decoding the message only using analog audio. I know it is possible if we go with digital audio.
Is this possible? If so, it would be great if someone can give me a some practical implementations of this.