Electronic hearing aid with gain control means for eliminating low frequency noise

A hearing aid device for the compensation of hearing deficiencies and for enhancing the intelligibility of audio-frequency speech signals corrupted by low frequency noise, said device comprising:

• a signal input transducer for converting input audio speech signals to electric speech signals,
• an output terminal adapted for connection to an output transducer for supplying acoustic output signals compensated for a hearing deficiency of a hearing-impaired person, and
• a control circuit having an input terminal connected between the output side of said input transducer and said output terminal, said control circuit comprising:
• summing means for summing signals applied thereto and producing a sum signal;
• a low-frequency channel, including a first band-pass filter, connected between said input terminal and said summing means for coupling to said summing means a low-frequency signal which is substantially free of frequency components above a selected frequency;
• a high-frequency channel connected in parallel with said low-frequency channel between said input terminal and said summing means and comprising:
• a second band-pass filter connected to said input terminal for producing from said electric speech signal a high-frequency signal which is substantially free of frequency components below said selected frequency,
• a variable gain amplifier connected to the output of said high-pass filter and having a gain control terminal and an output terminal, for compressing said high-frequency signal and producing a compressed high-frequency signal at its output terminal,
• means for generating a control signal for controlling the gain of said amplifier including means connected to the output of said high-frequency filter for controllably amplifying said high-frequency signal, means for rectifying said amplified high-frequency signal, and means for comparing the level of such rectified high-pass signal against a reference level and applying to said gain control terminal a signal proportional to the difference, for varying the gain of said amplifier inversely with the amplitude of said rectified high-frequency signal, and
• a potentiometer connected between the output terminal of said amplifier and said summing means for coupling a controllable portion of said compressed high-frequency signal to said summing means;
• a power amplifier having an input terminal and an output terminal connected to said device output terminal;
• and
• a potentiometer connected between the output of said summing means and the input terminal of said power amplifier for coupling a controllable portion of said sum signal to said power amplifier.