Detection of tonal signals

A method for detecting initiation/termination of a speech signal for a speech storage device, the method comprising:

• receiving an input signal, wherein at least a portion of said input signal includes a speech signal;
• calculating a zero-crossing rate signal based on said input signal;
• performing a differentiation operation with respect to time to generate a differentiated zero-crossing rate signal;
• integrate an absolute value of the differentiated zero-crossing rate signal in order to compute a series of resultant values;
• determining initiation/termination of said speech signal based on said series of resultant values, wherein said determining initiation/termination of said speech signal includes generating a control signal which indicates initiation/termination of said speech signal;
• wherein said control signal is used to control storage of said speech signal.

A system for detecting termination of a speech message for a speech storage device, the system comprising:

• an input for receiving an input signal, wherein at least a portion of said input signal includes a speech message signal;
• a zero-crossing rate calculator coupled to said input for computing a zero-crossing rate signal based upon said input signal;
• a differentiation unit coupled to said zero-crossing rate calculator which receives said zero-crossing rate signal from said zero-crossing rate calculator, wherein the differentiation unit is configured to perform a differentiation operation with respect to time to produce a differentiated zero-crossing rate sign;
• a discriminator coupled to said differentiation unit which receives said differentiated zero-crossing rate signal, wherein said discriminator comprises a magnitude integration unit which is configured to integrate an absolute value of said differentiated zero-crossing rate signal to generate a series of resultant values, wherein said discriminator determines termination of said speech message signal within said input signal based on the series of resultant values;
• wherein said discriminator generates an output signal indicating termination of said speech message signal, wherein said output signal is used to control storage of said speech message signal.

A telephone answering device comprising:

• an input for receiving an input signal, wherein at least a portion of said input signal includes a speech message signal;
• a memory media which receives and stores said input signal;
• a message-termination detector coupled to said input, and operable to determine termination of said speech message signal within said input signal, wherein said message-termination detector generates a control signal indicating termination of said speech message signal;
• wherein said telephone answering device discontinues storage of said input signal in said memory media in response to said control signal indicating termination of said speech message signal;
• wherein said message-termination detector comprises:
• a zero-crossing rate calculator coupled to said input for computing a zero-crossing rate signal based upon said input signal;
• a differentiation unit coupled to said zero-crossing rate calculator which receives said zero-crossing rate signal from said zero-crossing rate calculator, wherein the differentiation unit is configured to perform a differentiation operation with respect to time to produce a differentiated zero-crossing rate signal;
• a discriminator coupled to said differentiation unit which receives said differentiated zero-crossing rate signal, wherein said discriminator comprises a magnitude integration unit which is configured to integrate an absolute value of said differentiated zero-crossing rate signal to generate a series of resultant values, wherein said discriminator determines termination of said speech message signal within said input signal based on the series of resultant values.