Signal processing circuit and method for increasing speech intelligibility

A method of processing an audio signal in a hearing aid to increase speech intelligibility to a human, comprising:

• receiving an audio signal;
• passing the audio signal through a signal processing circuit having an output, and outputting a modified audio signal from the output;
• phase aligning the modified audio signal with an unpassed audio signal present at the output;
• amplifying frequencies of the audio signal differentially to amplify a second frequency range comprising second speech formant frequencies of the audio signal with an amplified gain that is greater than a gain amplification of a first frequency range comprising first speech formant frequencies;
• and
• controlling the amplified gain based on an inaudible signal tone;
• the controlling the amplified gain based on the inaudible signal tone to effect the amplified gain regardless of a presence of noise in the first and second frequency ranges and to substantially prevent regenerative oscillation the amplified audio signal.

A hearing aid signal processing circuit to increase speech intelligibility to a human, the human having at least one eardrum, comprising:

• a receiving circuit to receive an audio signal;
• a gain amplifying circuit to differentially amplify a first frequency range comprising first speech formant frequencies and a second frequency range comprising second speech formant frequencies of the audio signal as a function of a difference in dedibels to restore a sound pressure level of the second frequency range to a normal level dependent on the human and a frequency of the audio signal;
• and
• a feedback circuit to control gain amplification of only one of the frequency ranges based on a sensed level of an inaudible continuous signal tone;
• the feedback circuit's control of the gain amplification based on the sensed level of the inaudible signal tone to substantially prevent regenerative oscillation of the audio signal.