NOISE CANCELLATION SYSTEM

• US 20110130176A1
• Filed: 06/24/2009
• Published: 06/02/2011
• Est. Priority Date: 06/27/2008
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Wolfson Microelectronics plc
• Inventors: Graham, Clive Robert, Magrath, Anthony James
• Granted Patent: US 8,682,250 B2
• Time in Patent Office: Days
• US Class Current: 455/570
• CPC Class Codes: G10K 11/17823 Reference signals, e.g. ambient acoustic environment
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17873 using a reference signal without an error signal, e.g. pure feedforward
• 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 2210/1081 Earphones, e.g. for telephones, ear protectors or headsets
• CPC Class Codes: G10K 2210/3027 Feedforward
• CPC Class Codes: G10L 2021/02082 the noise being echo, reverberation of the speech
• CPC Class Codes: G10L 2021/02165 Two microphones, one receiving mainly the noise signal and the other one mainly the speech signal
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: H03H 21/0012 Digital adaptive filters

Abstract

A noise cancellation system for an audio system such as a mobile phone handset, or a wireless phone headset has a first input for receiving a first audio signal from one or more microphone positioned to receive ambient noise, and a second input for receiving a second audio signal from a microphone positioned to detect the user?s speech, as well as a third input for receiving a third audio signal for example representing the speech of a person to whom the user is talking. A first noise cancellation block receives the first audio signal and generates a first noise cancellation signal, and this is combined with the third audio signal to form a first audio output signal. A second noise cancellation block receives at least a part of the first audio signal and said second audio signal and applying noise cancellation to generate a second audio output signal.

Claims

1. A noise cancellation system, comprising:

a first input for receiving a first audio signal;

a second input for receiving a second audio signal;

a third input for receiving a third audio signal;

a first noise cancellation block for receiving said first audio signal and generating a first noise cancellation signal;

a first combiner, for combining said third audio signal and said first noise cancellation signal and generating a first audio output signal;

a second noise cancellation block for receiving at least a part of said first audio signal and said second audio signal and applying noise cancellation to generate a second audio output signal.

2. A noise cancellation system as claimed in claim 1, wherein the first audio signal comprises signals from a plurality of microphones, and comprising:

a combiner for combining the signals from the plurality of microphones and passing the combined the signals to the first noise cancellation block,

wherein the signal from only one of the microphones is passed to the second noise cancellation block.

3. A noise cancellation system as claimed in claim 2, further comprising:

a selector, for selecting the signal from only one of the microphones, and for passing the selected signal to the second noise cancellation block.

4. A noise cancellation system as claimed in claim 3, wherein the selector comprises a level detector, for selecting the largest signal of the signals from the plurality of microphones.

5. A noise cancellation system as claimed in claim 1, wherein the first audio signal comprises signals from a plurality of microphones, and comprising:

a combiner for combining the signals from the plurality of microphones and passing the combined the signals to the first noise cancellation block and to the second noise cancellation block.

6. A noise cancellation system as claimed in claim 1, wherein the first noise cancellation block comprises a feedforward noise cancellation block.

7. A noise cancellation system as claimed in claim 6, wherein said first noise cancellation block comprises a 1-bit digital filter.

8. A noise cancellation system as claimed in claim 6, wherein said first noise cancellation block comprises:

a digital filter, for receiving said signal representative of ambient noise, said signal representative of ambient noise having a first sample rate;

a decimator, connected to the input to receive the signal representative of ambient noise and to generate a decimated signal at a second sample rate lower than the first sample rate; and

a processor, wherein the processor comprises;

an emulation of the digital filter, connected to receive the decimated signal and to generate an emulated filter output; and

a control circuit, for generating a control signal on the basis of the emulated filter output,

wherein the control signal is applied to the digital filter to control a filter characteristic thereof.

9. A noise cancellation system as claimed in claim 8, wherein the processor comprises:

a source input, for receiving said audio signal; and

an adder, for forming a sum of the emulated filter output and the audio signal,

wherein the control circuit is configured to generate the control signal on the basis of a comparison between said sum of the emulated filter output and the audio signal and a threshold value.

10. A noise cancellation system as claimed in claim 8, wherein the emulation of the digital filter comprises a lower order approximation of the digital filter.

11. A noise cancellation system as claimed in claim 10, wherein the digital filter comprises a sixth order IIR filter, and the emulation of the digital filter comprises a second order approximation of the digital filter.

12. A noise cancellation system as claimed in claim 8, wherein the digital filter comprises a fixed part and an adaptive part.

13. A noise cancellation system as claimed in claim 12, wherein the emulation of the digital filter comprises an emulation of the adaptive part of the digital filter.

14. A noise cancellation system as claimed in claim 8, wherein the filter characteristic is a cut-off frequency of the digital filter.

15. A noise cancellation system as claimed in claim 1, wherein the second noise cancellation block comprises a feedback noise cancellation block.

16. An audio system, comprising a noise cancellation system as claimed in claim 1, and further comprising:

at least one first microphone, positioned for detecting ambient noise, and for supplying the first audio signal to the first input of the noise cancellation system.

17. An audio system as claimed in claim 16, comprising a plurality of first microphones, and for supplying the first audio signal to the first input of the noise cancellation system.

18. A communications handset, comprising an audio system as claimed in claim 17, wherein the plurality of first microphones are positioned around a loudspeaker of said handset.

19. A communications handset as claimed in claim 18, in the form of a mobile telephone.

20. An audio system, comprising a noise cancellation system as claimed in claim 1, and further comprising:

at least one second microphone, positioned for detecting a voice of a user, and for supplying the second audio signal to the first input of the noise cancellation system.

21. An audio system, comprising a noise cancellation system as claimed in claim 1, and further comprising:

a loudspeaker, for receiving the first audio output signal.

22. An audio system, comprising a noise cancellation system as claimed in claim 1, and further comprising:

a transmitter, for transmitting the second audio output signal to a remote listener.