Method and system for sub-audible signaling

A non-transitory computer-readable storage medium containing a plurality of program instructions executable by a processor, comprising:

• an instruction segment for embedding in a second block of a received signal having a first block and second block an echo of the first block of the signal to create a first modified second block of the signal in accordance with a received first digital code, a magnitude of the echo being a magnitude of the first block of the signal multiplied by a first modifier value, a sign of the first modifier value being based on a binary digit of a corresponding bit of the first digital code;
• an instruction segment for modulating the power of the first modified second block of the signal to create a second modified second block of the signal in accordance with a received second digital code;
• an instruction segment for determining whether an amplitude of the first modified second block of the signal falls within a predetermined range, the instruction segment including:
• instructions for determining an average power of a series of blocks of the signal, the series of blocks including at least the first block of the signal, and
• instructions for comparing the amplitude of the first modified second block of the signal to the average power of the series of block;
• and
• an instruction segment for sending a modified signal including the second modified second block of the signal.

A non-transitory computer-readable storage medium containing a plurality of program instructions executable by a processor, comprising:

• an instruction segment for embedding in a second block of a received signal having a first block and second block an echo of the first block of the signal to create a first modified second block of the signal in accordance with a received first digital code, a magnitude of the echo being a magnitude of the first block of the signal multiplied by a first modifier value, a sign of the first modifier value being based on a binary digit of a corresponding bit of the first digital code;
• an instruction segment for determining whether the power of the first modified second block of the signal falls within a predetermined range, said instruction segment including:
• an instruction segment for determining the power of each block in a series of blocks of the signal, the series of blocks including at least the first block of the signal;
• and
• an instruction segment for comparing the power of the first modified second block of the signal to a function of the powers of the individual blocks in the series;
• an instruction segment for modulating the power of the first modified second block of the signal to create a second modified second block of the signal in accordance with a received second digital code, the power of the first modified second block of the signal modulated when the power of the first modified second block of the signal does not fall within the predetermined range.

A method, comprising:

• receiving a first digital code and a second digital code;
• receiving a first block and a second block of a signal;
• embedding an echo of the first block of the signal in the second block of the signal to create a first modified second block of the signal in accordance with the first digital code;
• determining whether a power of the first modified second block of the signal falls within a predetermined range, said determining including:
• (a) determining an average power of a series of blocks of the signal, the series of blocks including at least the first block of the signal, and (b) comparing the power of the first modified second block of the signal to the average power of the series of blocks;
• when the power of the first modified second block of the signal does not fall within the predetermined range, modulating the power of the first modified second block of the signal to create a second modified second block of the signal in accordance with the second digital code;
• and
• sending a modified signal including the second modified second block of the signal.