Audio adjustment method and associated audio adjustment circuit for active noise cancellation

1. An active noise cancellation (ANC) circuit, applicable to an electronic device, the ANC circuit comprising:

an audio input unit, configured to transmit an audio to be broadcast or a sound testing signal as a first time domain signal;

an audio receiver, configured to receive a background sound as a second time domain signal, wherein the background sound corresponds to the audio to be broadcast or the sound testing signal; and

a channel estimation unit, configured to receive the first time domain signal and the second time domain signal, perform time-frequency conversion upon the first time domain signal and second time domain signal to obtain a first frequency domain signal and a second frequency domain signal respectively, and generate a frequency response according to the first frequency domain signal and the second frequency domain signal;

wherein the frequency response is configured to adjust an active noise cancelling coefficient of the ANC circuit to improve a noise cancellation effect, the frequency response is transmitted to a filtering design unit, the filtering design unit generates a filtering coefficient to improve the active noise cancelling coefficient according to the frequency response, the filtering design unit is configured to generate an adjusted active noise cancelling coefficient according to the filtering coefficient, and feed the adjusted active noise cancelling coefficient back to the audio to be broadcast or the sound testing signal for calculating a difference between a phase of the first time domain signal and a phase of the second time domain signal.

2. The ANC circuit of claim 1 , wherein the first time domain signal and the second time domain signal are two time domain signals at a same time.

3. The ANC circuit of claim 1 , wherein the audio to be broadcast and the sound testing signal comprises:

a first feature within 0 to 200 Hz;

a second feature within 200 Hz to 500 Hz; and

a third feature beyond 500 Hz.

4. The ANC circuit of claim 1 , further comprising:

a multiplexer, configured to select one of the audio to be broadcast and the sound testing signal to be the first time domain signal.

5. The ANC circuit of claim 1 , further comprising:

a conversion unit, configured to perform a discrete Fourier transform (DFT) or a short-time Fourier transform (STFT) upon the first time domain signal and the second time domain signal to obtain the first frequency domain signal and the second frequency domain signal respectively.

6. The ANC circuit of claim 5 , wherein the channel estimation unit performs orthogonal frequency-division multiplexing (OFDM) channel estimation according to the first frequency domain signal and the second frequency domain signal to generate the frequency response.

7. The ANC circuit of claim 6 , wherein the channel estimation unit is a pilot-aided OFDM channel estimation unit.

8. The ANC circuit of claim 1 , wherein the electronic device comprises a speaker, wherein the frequency response is configured to adjust the active noise cancelling coefficient of the ANC circuit to reduce at least one of impact of background noise, secondary path response or feedback path neutralization (FBPN) on an audio broadcast by the speaker.

9. The ANC circuit of claim 1 , wherein the electronic device is implemented as an earphone or audio system.

10. An active noise cancellation (ANC) adjustment method, applicable to an ANC circuit, the ANC circuit comprising an audio receiver and an audio input unit, the audio receiver being configured to receive sounds, the ANC adjustment method comprising:

generating a first time domain signal according to an audio to be broadcast or a sound testing signal by the audio input unit;

generating a second time domain signal according to a background sound received by the audio receiver, wherein the background sound corresponds to the audio to be broadcast or the sound testing signal;

performing time-frequency conversion upon the first time domain signal and second time domain signal to obtain a first frequency domain signal and a second frequency domain signal respectively;

generating a frequency response according to the first frequency domain signal and the second frequency domain signal; and

adjusting an active noise cancelling coefficient of the ANC circuit according to the frequency response to improve a noise cancellation effect;

wherein the frequency response is transmitted to a filtering design unit, the filtering design unit generates a filtering coefficient to improve the active noise cancelling coefficient according to the frequency response, and

the step of adjusting the active noise cancelling coefficient of the ANC circuit according to the frequency response to improve the noise cancellation effect comprises:

generating an adjusted active noise cancelling coefficient according to the filtering coefficient, and feeding the adjusted active noise cancelling coefficient back to the audio to be broadcast or the sound testing signal for calculating a difference between a phase of the first time domain signal and a phase of the second time domain signal.

11. The ANC adjustment method of claim 10 , wherein the first time domain signal and the second time domain signal are two time domain signals at a same time.

12. The ANC adjustment method of claim 10 , wherein the audio to be broadcast and the sound testing signal comprises:

a first feature within 0 to 200 Hz;

a second feature within 200 Hz to 500 Hz; and

a third feature beyond 500 Hz.

13. The ANC adjustment method of claim 10 , wherein the step of performing the time-frequency conversion upon the first time domain signal and second time domain signal to obtain the first frequency domain signal and the second frequency domain signal respectively comprises:

performing a discrete Fourier transform (DFT) or a short-time Fourier transform (STFT) upon the first time domain signal and the second time domain signal to obtain the first frequency domain signal and the second frequency domain signal respectively.

14. The ANC adjustment method of claim 13 , wherein the step of generating the frequency response according to the first frequency domain signal and the second frequency domain signal comprises:

performing orthogonal frequency-division multiplexing (OFDM) channel estimation according to the first frequency domain signal and the second frequency domain signal to generate the frequency response.

15. The ANC adjustment method of claim 14 , wherein the channel estimation is a pilot-aided OFDM channel estimation.

16. The ANC adjustment method of claim 10 , wherein the ANC circuit is coupled to a speaker, and the step of adjusting the active noise cancelling coefficient of the ANC circuit according to the frequency response to improve the noise cancellation effect comprises:

adjusting the active noise cancelling coefficient of the ANC circuit to reduce at least one of impact of background noise, secondary path response or feedback path neutralization (FBPN) on an audio broadcast by the speaker.