ACTIVE NOISE REDUCTION METHOD USING PERCEPTUAL MASKING

• US 20110026724A1
• Filed: 07/29/2010
• Published: 02/03/2011
• Est. Priority Date: 07/30/2009
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Doclo, Simon
• Granted Patent: US 9,437,182 B2
• Time in Patent Office: Days
• US Class Current: 381/71.8
• CPC Class Codes: G10K 11/17817 between the output signals and the error signals, i.e. secondary path
• CPC Class Codes: G10K 11/17827 Desired external signals, e.g. pass-through audio such as music or speech
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17857 Geometric disposition, e.g. placement of microphones
• CPC Class Codes: G10K 11/17881 the reference signal being an acoustic signal, e.g. recorded with a microphone
• CPC Class Codes: G10K 11/17885 additionally using a desired external signal, e.g. pass-through audio such as music or speech
• CPC Class Codes: G10K 2210/1053 Hi-fi, i.e. anything involving music, radios or loudspeakers
• CPC Class Codes: G10K 2210/108 Communication systems, e.g. where useful sound is kept and noise is cancelled
• CPC Class Codes: H04R 1/1083 Reduction of ambient noise active noise reduction per se G10K11/175; protective devices for the ear, e.g. providing acoustic protection A61F11/06
• CPC Class Codes: H04R 2460/01 Hearing devices using active noise cancellation

Abstract

A method of active noise reduction is described which comprises receiving an audio signal (132) to be played, receiving a noise signal (105, 107, 116, 118, 126), indicative of ambient noise (111), from at least one microphone (104, 106), and generating a noise cancellation signal (114) depending on both, said audio signal (132) and said noise signal (105, 107, 116, 118, 126).

Claims

1. Method of active noise reduction, the method comprising:

receiving an audio signal to be played;

receiving at least one noise signal from at least one microphone, said noise signal being indicative of an ambient noise;

generating a noise cancellation signal depending on both said audio signal and said at least one noise signal.

2. Method according to claim 1, wherein generating said noise cancellation signal comprises:

providing an active noise reduction filter having a plurality of filter parameters which define filter characteristics of the active noise reduction filter,

providing optimized values for said filter parameters of said active noise reduction filter depending on said audio signal and at least one said noise signal; and

filtering at least one of said at least one noise signal with said active noise reduction filter by using said optimized values for said filter parameters.

3. Method according to claim 2, further comprising:

determining said optimized values for said filter parameters in an optimization procedure, said optimization procedure using spectro-temporal characteristics of said audio signal and spectro-temporal characteristics of said at least one noise signal to improve masking of a perception of residual noise by said audio signal.

4. Method according to claim 2, the method further comprising:

determining a frequency masking threshold from the audio signal;

determining a desired active performance indicating how much the ambient noise must be suppressed such that it is masked by the audio signal; and

optimizing said filter parameters so as to decrease a difference between an actual active performance and a desired active performance.

5. Method according to claim 4, wherein said desired active performance is determined from a difference between the frequency masking threshold and a power spectral density of said at least one noise signal.

6. Method according to claim 1, wherein one of said at least one noise signal is a feedforward signal obtained by receiving a reference microphone signal from a reference microphone which is configured for receiving said ambient noise and for generating in response thereto said reference microphone signal.

7. Method according to claim 1, wherein one of said at least one noise signal is a feedback signal obtained by receiving an error microphone signal from an error microphone which is configured for receiving said ambient noise, said noise cancellation signal filtered by a secondary path between a loudspeaker and said error microphone, and said audio signal filtered by said secondary path, and for generating in response hereto said error microphone signal.

8. Method according to claim 1, wherein one of said at least one noise signal is an ambient noise estimation signal, obtained by subtracting an estimate of a secondary path signal from an error microphone signal, wherein the secondary path signal is a signal received by the error microphone which corresponds to a sum of said audio signal and said noise cancellation signal, and wherein said error microphone signal is generated by an error microphone which is configured for receiving said ambient noise, said noise cancellation signal and said audio signal, and for generating in response thereto said error microphone signal.

9. Cancellation signal generator comprising:

a first input for receiving an audio signal to be played;

a second input for receiving from at least one microphone at least one noise signal indicative of an ambient noise;

said cancellation signal generator being configured for generating a noise cancellation signal depending on both said audio signal and said at least one noise signal.

10. Cancellation signal generator according to claim 9, said cancellation signal generator comprising:

a power spectrum unit for providing, based on said at least one noise signal, an ambient noise power spectrum density corresponding to said ambient noise;

a psychoacoustic masking model unit for generating, based on said audio signal, a frequency masking threshold, said frequency masking threshold indicating a power below which a residual noise is masked by the audio signal; and

a subtraction unit for calculating, as a desired active performance, a difference of said ambient noise power spectrum density and said frequency masking threshold.

11. Cancellation signal generator according to claim 9, further comprising:

an active noise reduction filter having filter characteristics depending on both said audio signal and said at least one noise signal;

wherein said active noise reduction filter is configured for filtering at least one of said at least one noise signal to thereby generate said noise cancellation signal.

12. Cancellation signal generator according to claim 11, further comprising:

said active noise reduction filter having a plurality of filter parameters which define said filter characteristics of the active noise reduction filter, and

a filter optimization unit configured for providing optimized values for said filter parameters of said active noise reduction filter depending on said audio signal and said at least one noise signal.

14. Active noise reduction audio system comprising:

a cancellation signal generator according to claim 9;

a loudspeaker for playing said audio signal; and

said at least one microphone for providing said at least one noise signal.

13. (canceled)

15. (canceled)