An improved embedded signaling apparatus and method of embedding data into audio
signals occurring at substantially zero decibel levels is disclosed. Embedding
is accomplished at such low inaudible levels by modifying an embedded signaling
encoder with a dither generator, dither adder and dither subtracter that generates,
adds and subtracts dither signals, of equal magnitude, to audio signals at specified
bit rates. Because the dither signal is used substantially within the encoder and
is substantially canceled before final output, the dither signal provides an additional
signal level, depth or dimension in the absence of audio data. Thus, whenever music
or other audio data that will ultimately become audible reaches a very low decibel
level, such as during periods of silence on a CD, the effectiveness of embedding
data into such low level signals is not impaired. The embedded signaling encoder
of the present invention can also be used for authentication purposes.