Coding a masked data channel in a radio signal

A system for supplementing an audio signal with auxiliary data in an inaudible channel, the system comprising:

• an audible radio signal source comprising at least a left channel and a right channel;
• a digital signal processor programmed to transform said audible radio signal source into a frequency domain representation comprising a plurality of frequency component portions of said audible radio signal;
• a comparator coupled to said digital signal processor and having an established imperceptible interaural phase differential (IPD), said comparator identifying selected ones of said frequency component portions having corresponding phase values which do not exceed said imperceptible IPD;
• and,
• an encoder configured to encode a digital auxiliary data signal into said audible radio signal by modifying said corresponding phase values to correspond to individual bit values of said digital auxiliary data.

A machine readable storage having stored thereon a computer program for coding auxiliary data in an inaudible channel in an audio signal, the computer program comprising a routine set of instructions for causing the machine to perform the steps of:

• establishing an upper bound imperceptible interaural phase difference (IPD) between at least two audible channels in the audio signal below which differences in phase between said channels cannot be audibly detected;
• identifying frequency component portions of the audio signal corresponding to said channels having a phase difference which does not exceed said established upper bound IPD;
• and,
• modifying phase differences between said identified frequency component portions to encode digital auxiliary data in the audio signal,
• whereby the encoded digital auxiliary data can be decoded by detecting said modified phase differences between said identified frequency component portions of the audio signal.