Parallel active noise reduction (ANR) and hear-through signal flow paths in acoustic devices
Technology described in this document can be embodied in a method that includes receiving an input signal captured by one or more sensors associated with an active noise reduction (ANR) device, processing the input signal using a first filter disposed in an ANR signal flow path to generate a first signal for an acoustic transducer of the ANR device, and processing the input signal in a pass-through signal flow path disposed in parallel with the ANR signal flow path to generate a second signal for the acoustic transducer. The pass-through signal flow path is configured to allow at least a portion of the input signal to pass through to the acoustic transducer in accordance with a variable gain associated with the pass-through signal flow path. The method also includes generating an output signal for the acoustic transducer based on combining the first signal with the second signal.
1. A method comprising:
receiving an input signal captured by one or more sensors associated with an active noise reduction (ANR) device;
processing the input signal using a first filter disposed in an ANR signal flow path to generate a first signal for an acoustic transducer of the ANR device;
processing the input signal in a pass-through signal flow path disposed in parallel with the ANR signal flow path to generate a second signal for the acoustic transducer, wherein the pass-through signal flow path is configured to allow at least a portion of the input signal to pass through to the acoustic transducer in accordance with a variable gain associated with the pass-through signal flow path; and
generating an output signal for the acoustic transducer based on combining the first signal with the second signal.
2. The method of claim 1 , wherein the one or more sensors comprise a feedforward microphone of the ANR device.
3. The method of claim 1 , wherein the first filter comprises a filter bank that includes a plurality of selectable digital filters, each digital filter in the filter bank corresponding to a value of the variable gain associated with the pass-through signal flow path.
4. The method of claim 1 , wherein the pass-through signal flow path comprises a second filter.
5. The method of claim 4 , wherein coefficients of each of the first filter and the second filter are substantially fixed.
6. The method of claim 4 , wherein a set of coefficients of the first filter is determined substantially independently of a set of coefficients of the second filter.
7. The method of claim 1 , wherein a first latency associated with the ANR signal flow path is substantially different from a second latency associated with the pass-through signal flow path.
8. The method of claim 1 , further comprising:
receiving a user-input indicative of the variable gain associated with the pass-through signal path; and
adjusting a variable gain amplifier (VGA) disposed in the pass-through signal flow path in accordance with the user-input.
9. The method of claim 1 , further comprising:
receiving a user-input indicative of the variable gain associated with the pass-through signal flow path; and
selecting coefficients of at least one of the first filter and a second filter disposed in the pass-through signal flow path in accordance with the user-input.
10. The method of claim 9 , wherein the coefficients of the at least one of the first filter and the second filter are determined in accordance with a target spectral characteristic of the corresponding filter.
11. The method of claim 10 , wherein the target spectral characteristic is spectral flatness.
12. The method of claim 1 , wherein the ANR signal flow path and pass-through signal flow path are disposed in a feedforward signal flow path for the ANR device.
13. 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;
an acoustic transducer configured to generate output audio;
a first filter disposed in an ANR signal flow path of the ANR device, the first filter configured to process the input signal to generate a first signal for the acoustic transducer of the ANR device; and
a pass-through signal flow path disposed in parallel with the ANR signal flow path, the pass-through signal flow path configured to generate a second signal for the acoustic transducer, wherein the pass-through signal flow path is configured to allow at least a portion of the input signal to pass through to the acoustic transducer in accordance with a variable gain associated with the pass-through signal flow path,
wherein the acoustic transducer is driven by an output signal that is a combination of the first signal and the second signal.
14. The ANR device of claim 13 , wherein the one or more sensors comprise a feedforward microphone of the ANR device.
15. The ANR device of claim 13 , wherein the ANR filter comprises a filter bank that includes a plurality of selectable digital filters, each digital filter in the filter bank corresponding to a value of the variable gain associated with the pass-through signal flow path.
16. The ANR device of claim 13 , wherein the pass-through signal flow path comprises a second filter.
17. The ANR device of claim 16 , wherein coefficients of each of the first filter and the second filter are substantially fixed.
18. The ANR device of claim 16 , wherein a set of coefficients of the first filter is determined substantially independently of a set of coefficients of the second filter.
19. The ANR device of claim 13 , wherein a first latency associated with the ANR signal flow path is substantially different from a second latency associated with the pass-through signal flow path.
20. The ANR device of claim 13 , further comprising a variable gain amplifier (VGA) disposed in the pass-through signal flow path, the VGA configured to control the variable gain associated with the pass-through signal flow path in accordance with user-input received using an input device.
21. The ANR device of claim 20 , further comprising one or more processing devices configured to select coefficients of at least one of the first filter and a second filter disposed in the pass-through signal flow path in accordance with the user-input.
22. The ANR device of claim 21 , wherein the coefficients of the at least one of the first filter and the second filter are determined in accordance with a target spectral characteristic of the corresponding filter.
23. The ANR device of claim 22 , wherein the target spectral characteristic is spectral flatness.
24. The ANR device of claim 13 , wherein the ANR signal flow path and pass-through signal flow path are disposed in a feedforward signal flow path for the ANR device.
25. 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 captured by one or more sensors associated with an active noise reduction (ANR) device;
processing the input signal using a first filter disposed in an ANR signal flow path to generate a first signal for an acoustic transducer of the ANR device;
processing the input signal in a pass-through signal flow path in parallel with the ANR signal flow path to generate a second signal for the acoustic transducer, wherein the pass-through signal flow path is configured to allow at least a portion of the input signal to pass through to the acoustic transducer in accordance with a variable gain associated with the pass-through signal flow path; and
generating an output signal for the acoustic transducer based on combining the first signal with the second signal.