System and method for SAP FM demodulation

A method for demodulation of a digital signal, said method comprising:

• isolating desired signal information from an audio signal;
• phase shifting a copy of said desired signal information to produce a phase shifted copy of said desired information;
• delaying a copy of said desired signal information using a non-unity delay to produce a delayed copy of said desired signal information;
• and
• FM demodulating said desired signal information using said non-unity delay and a discrete time index with a combination of said phase shifted copy of said desired signal information and said delayed copy of said desired signal information to produce an FM demodulated signal.

A method for simplification of secondary audio program signal demodulation, said method comprising:

• using a bandpass filter to isolate said secondary audio program signal in a composite audio signal;
• using a Hilbert filter to produce a signal in phase quadrature;
• using a delay module to produce a delayed secondary audio program signal using a delay, wherein said delay module is capable of applying a non-unity delay to said secondary audio program signal to produce said delayed secondary audio program signal;
• and
• using a simple approximation for FM demodulation of said secondary audio program signal based on said delay, a time index, said delayed secondary audio program signal, and said signal in quadrature phase.