Noise cancellation system with lower rate emulation
View Patent ↗A noise cancellation system, comprising: an input for a digital signal, the digital signal having a first sample rate; a digital filter, connected to the input to receive the digital signal; a decimator, connected to the input to receive the digital signal and to generate a decimated signal at a second sample rate lower than the first sample rate; and a processor. 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. The control signal is applied to the digital filter to control a filter characteristic thereof.
1. A noise cancellation system, comprising:
an input, for receiving a digital signal;
a digital filter, having at least a high pass filter characteristic, for receiving the digital signal and generating a filter output signal;
a filter emulator, for receiving the digital signal and forming a representation of the filter output signal;
a source input, for receiving a wanted signal;
an adder, for forming a sum of amplitudes of the wanted signal and the representation of the filter output signal; and
an amplitude detector, for generating a detection signal based on a comparison of said sum of amplitudes with a threshold,
wherein the detection signal is applied to the digital filter to control a cut-off frequency thereof.
2. A noise cancellation system as claimed in claim 1 , wherein the amplitude detector generates the detection signal based on a comparison of an absolute value of said sum of amplitudes with a threshold.
3. A noise cancellation system as claimed in claim 1 , wherein the amplitude detector generates the detection signal based on a comparison of a root mean square value of said sum of amplitudes with a threshold.
4. A noise cancellation system as claimed in claim 1 , wherein the digital signal has a first sampling rate, and further comprising:
a decimator, for producing a decimated input signal having a second sampling rate lower than the first sampling rate, and
wherein the decimated input signal is applied to the emulation of the digital filter.
5. A noise cancellation system as claimed in claim 1 , wherein said noise cancellation system is a feedforward system.
6. A noise cancellation system as claimed in claim 1 , wherein said noise cancellation system is a feedback system.
7. An integrated circuit, comprising:
a noise cancellation system as claimed in claim 1 .
8. A mobile phone, comprising:
an integrated circuit as claimed in claim 7 .
9. A pair of headphones, comprising:
an integrated circuit as claimed in claim 7 .
10. A pair of earphones, comprising:
an integrated circuit as claimed in claim 7 .
11. A headset, comprising:
an integrated circuit as claimed in claim 7 .
12. A method of controlling a filter for a noise cancellation system, comprising:
receiving a digital signal, the digital signal having a first sample rate;
filtering the digital signal in a digital filter, to generate a filter output signal;
emulating said digital filter, to generate an emulation output signal;
detecting an amplitude of said emulation output signal;
receiving a wanted signal;
forming a sum of amplitudes of the emulation output signal and the wanted signal;
generating a detection signal based on a comparison of said sum of amplitudes with a threshold; and
applying said detection signal to said digital filter, to control a cut-off frequency thereof.
13. A method as claimed in claim 12 , further comprising:
producing a decimated input signal having a second sampling rate lower than the first sampling rate,
wherein the decimated input signal is applied to the emulation of the digital filter.