Automatic gain control in an active noise reduction (ANR) signal flow path

An active noise reduction (ANR) device comprising:

• one or more sensors configured to generate an input signal indicative of an external environment of the ANR device;
• a first compensator configured to process a first frequency range of the input signal to generate a first signal for an acoustic transducer of the ANR device, wherein the first signal generated by the first compensator includes a first anti-noise signal configured to reduce a noise signal in the first frequency range;
• a second compensator disposed in parallel to the first compensator, the second compensator configured to process a second frequency range of the input signal to generate a second signal for the acoustic transducer, wherein the second signal generated by the second compensator includes a second anti-noise signal configured to reduce a noise signal in the second frequency range;
• a filter configured to filter the second signal to produce a filtered second signal;
• and
• one or more processing devices configured to:
• detect whether the filtered second signal satisfies a threshold condition by comparing the filtered second signal with a threshold,
• responsive to detecting that the filtered second signal satisfies the threshold condition,
• generating a control signal configured to adjust a variable gain amplifier that attenuates the second signal without attenuating the first signal, and
• generating a combined signal for the acoustic transducer by summing either (i) the first signal and the attenuated second signal, and
• responsive to detecting that the filtered second signal fails to satisfy the threshold condition,
• generating the combined signal for the acoustic transducer by summing the first signal and the second signal.

One or more machine-readable storage devices having encoded thereon computer readable instructions for causing one or more processing devices to perform operations comprising:

• receiving an input signal representing audio captured by a microphone of an active noise reduction (ANR) headphone;
• causing a first compensator to process a first frequency range of the input signal to generate a first signal for an acoustic transducer of the ANR headphone, wherein the first signal generated by the first compensator includes a first anti-noise signal configured to reduce a noise signal in the first frequency range;
• causing a second compensator, disposed in parallel to the first compensator, to process a second frequency range of the input signal to generate a second signal for the acoustic transducer, wherein the second signal generated by the second compensator includes a second anti-noise signal configured to reduce a noise signal in the second frequency range;
• causing a filter to filter the second signal to produce the second signal to produce a filtered second signal;
• detecting whether the filtered second signal satisfies a threshold condition by comparing the filtered second signal with a threshold;
• and
• responsive to detecting that the filtered second signal satisfies the threshold condition,
• generating a control signal configured to adjust a variable gain amplifier that attenuates the second signal without attenuating the first signal, and
• generating a combined signal for the acoustic transducer by summing the first signal and the attenuated second signal;
• and
• responsive to detecting that the filtered second signal fails to satisfy the threshold condition,
• generating the combined signal for the acoustic transducer by summing the first signal and the second signal.