Ultrasonic Doppler sensor for speech-based user interface
View Patent ↗A method and system detect speech activity. An ultrasonic signal is directed at a face of a speaker over time. A Doppler signal of the ultrasonic signal is acquired after reflection by the face. Energy in the Doppler signal is measured over time. The energy over time is compared to a predetermined threshold to detect speech activity of the speaker in a concurrently acquired audio signal.
1. A method for detecting speech activity, comprising:
directing an ultrasonic signal at a face of a speaker over time;
acquiring a Doppler signal of the ultrasonic signal after reflection by the face;
measuring an energy in the Doppler signal over time; and
comparing the energy over time to a predetermined threshold to detect speech activity of the speaker.
2. The method of claim 1 , further comprising:
frequency demodulating the Doppler signal before the measuring.
3. The method of claim 2 , in which the frequency demodulation is into a range of frequency bands.
4. The method of claim 1 , further comprising:
sampling the Doppler signal; and
partitioning the samples into frames before the measuring.
5. The method of claim 4 , in which the frames overlap in time.
6. The method of claim 2 , further comprising:
extracting discrete Fourier transform (DFT) coefficients from the demodulated Doppler signal; and
measuring the energy from the DFT coefficients.
7. The method of claim 1 , further comprising:
filtering the Doppler signal to smooth the energy before the measuring.
8. The method of claim 7 , further comprising:
determining a medium of the energy over time before the comparing using the filtering.
9. The method of claim 1 , further comprising:
acquiring concurrently an audio signal while acquiring the Doppler signal; and
processing the audio signal only while detecting the speech activity.
10. The method of claim 1 , further comprising:
heterodyning the Doppler signal before the measuring.
11. The method of claim 1 , in which the ultrasonic signal is spatially narrow beam.
12. The method of claim 11 , in which the ultrasonic signal has a bandwidth corresponding to a bandwidth of the demodulated Doppler signal.
13. The method of claim 9 , in which the acquiring is performed with colocated sensors.
14. The method of claim 1 , in which a bandwidth of the ultrasonic signal corresponds to a bandwidth of frequencies at which articulator of the face move while speaking.
15. The method of claim 2 , in which the energy is obtained from an amplitude of the demodulated Doppler signal.
16. The method of claim 2 , in which the demodulating is similar to spectral-decomposition of the ultrasonic signal.
17. The method of claim 1 , further comprising:
sampling the ultrasonic signal to obtain overlapping frames.
18. A system for detecting speech activity, comprising:
a transmitter configured to direct an ultrasonic signal at a face of a speaker;
a receiver configured to acquire a Doppler signal of the ultrasonic signal after reflection by the face;
means for measuring an energy in the Doppler signal; and
means for comparing the energy to a threshold to detect speech activity.
19. An apparatus for detecting speech activity, comprising:
an emitter configured to direct an ultrasonic signal at a face of a speaker;
a transducer configured to acquire a Doppler signal of the ultrasonic signal after reflection by the face;
a microphone configured to acquire an audio signal; and
means coupled to the transducer and microphone to detect speech activity in the audio signal based on an energy of the Doppler signal.
20. The apparatus of claim 19 , in which the emitter, transducer and microphone are colocated.