Disclosed example apparatus select a first frequency from a set of frequencies based on a first symbol in a code, and select a first block size based on the first symbol and the code, a combination of the first block size and the first frequency to represent the first symbol. Disclosed example apparatus also synthesize a code frequency according to the first block size and the first frequency. Disclosed example apparatus further embed the code frequency in a first block of input audio samples of the audio having the first block size to form a block of encoded audio samples encoded with the first symbol, the code frequency and the first block of input audio samples to overlap in time.