Journal of the Institute of Electronics Engineers of Korea SP (대한전자공학회논문지SP)

The Institute of Electronics and Information Engineers (대한전자공학회)
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Improvement of Microphone Away Performance in the Low Frequencies Using Modulation Technique

변조 기법을 이용한 마이크로폰 어레이의 저주파 대역 특성 개선

  • Kim, Gi-Bak (School of Electrical Engineering, Seoul National University) ;
  • Cho, Nam-Ik (School of Electrical Engineering, Seoul National University)
  • Published : 2005.07.01
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Abstract

In this paper, we employ the modulation technique for improving the characteristics of beamformer in the low frequencies and thus improving the overall noise reduction performance. In the 1-dimensional uniform linear microphone arrays, we can suppress the narrowband noise component using the delay-and-sum beamforming. But, for the wideband noise signal, the delay-and-sum beamformer does not work well for the reduction of low frequency component because the inter-element spacing is usually set to avoid spatial aliasing at high frequencies. Hence, the beamwidth is not uniform with respect to each frequency and it is usually wider at the low frequencies. In order to obtain the beamwidth independent of frequencies, subarray systems[1][2][3][4] and multi-beamforming[5] have been proposed. However these algorithms need large space and more microphones since they are based on the theory that the size of the array is proportional to the wavelength of the input signal. In the proposed beamformer, we reduce the low frequency noise by using modulation technique that does not need additional sensors or non-uniform spacing. More Precisely, the array signals are split into subbands, and the low frequency components are shifted to high frequencies by modulation and reduced by the delay-and-sum beamforming techniques with small size microphone array. Experimental results show that the proposed technique Provides better performance than the conventional ones, especially in the low frequency band.

본 논문에서는 진폭 변조 기법을 이용하여 빔포머의 저주파 대역 특성을 개선함으로써 전체적인 잡음 제거 성능을 향상하고자 한다. 일차원 등간격 선형 마이크로폰 어레이를 사용하여 잡음 제거를 할 때, 협대역의 잡음 신호에 대해서는 delay-and-sum 빔포밍으로도 적절한 빔폭을 갖는 빔패턴이 형성되므로 효과적으로 잡음을 제거할 수 있다. 그러나 광대역 잡음 신호에서는 aliasing을 피하기 위해 고주파 신호에 맞게 마이크로폰들을 등간격으로 조정하면 저주파로 갈수록 빔폭이 털어져서 저주파 대역의 잡음은 잘 제거되지 않는다. 광대역 신호에 대해 일정한 빔폭을 갖게 하는 방법들로서 서브 어레이들을 이용한 빔포밍[1][2][3][4] 이나 멀티 빔포밍[5] 등이 제안되어 왔다. 하지만, 이러한 방법들은 주파수에 따라 마이크로폰 간격을다르게 해야 한다는 원리를 기반으로 하는 것이므로 저주파 대역에서도 고주파 대역에서와 같은 좁은 빔폭을 얻기 위해서는 어레이의 크기가 커져야 하는 단점이 있다. 제안하는 알고리즘은 통신에서 주로 사용하는 진폭 변조 기법을 빔포밍에 이용한 것으로서 저주파 대역 신호를 고주파 대역으로 옮김으로써 작은 크기의 마이크로폰 어레이에서도 저주파 대역 잡음을 줄일 수 있는 장점이 있다. 등간격 선형 마이크로폰 어레이에 제안된 방법을 적용한 실험 결과에서 기존의 방법들에 비해 잡음의 저주파 성분이 잘 제거됨을 알 수 있다.

Keywords

References

  1. D. B. Ward, R. A. Kennedy, and R. C. Williamson, 'Theory and design of broadband sensor arrays with frequency invariant far-field beam patterns,' J. Acoust. Soc. Amer., vol. 97, no. 2, pp. 1023-1034, Feb. 1995 https://doi.org/10.1121/1.412215
  2. M. Brandstein and D. B. Ward, Microphone Arrays : Signal Processing Techniques and Applications, Springer-Verlag, May 2001
  3. T Chou, 'Frequency-Independent Beamformer with Low Response Error,' in Proc. IEEE International Conference on Acoustics, S and Signal Processing, vol. 5, pp. 2995-2998, 1995 https://doi.org/10.1109/ICASSP.1995.479475
  4. R. J. Webster and T. N. Lang, 'Prescribed Sidelobes for the Constant Beamwidth Array,' IEEE Trans. Acoustics, Speech and Signal Processing, vol. 38, no. 4, April 1990 https://doi.org/10.1109/29.52716
  5. M. M. Goodwin and G. W. Elko, 'Constant Beamwidth Beamforming,' in Proc. IEEE International Conference on Acoustics, Speech and Signal Processing, vol. 1, pp. 169-172, 1993 https://doi.org/10.1109/ICASSP.1993.319082
  6. J. S. Lim and A. V. Oppenheim, 'All-pole modeling of degraded speech.' IEEE Trans. Acoust., Speech, Signal Processing, 26(3): 197 -210, June 1978 https://doi.org/10.1109/TASSP.1978.1163086
  7. S. F. BOLL, 'Suppression of acoustic noise in speech using spectral subtraction,' IEEE Trans. Acoust., Speech, Signal Processing, Vol.27, No.2, pp. 113-120, 1979 https://doi.org/10.1109/TASSP.1979.1163209
  8. Y. Ephraim and D. Malah, 'Speech Enhancement Using a Minimun Mean-Square Error Short-Time Spectral Amplitude Estimator,' IEEE Trans. Acoust., Speech, Signal Processing, 32(6):1109 -1121, December 1984 https://doi.org/10.1109/TASSP.1984.1164453
  9. S. Fischer, K. U. Simmer, 'Beamforming Microphone Arrays for Speech Acqusition in Noise Environments,' Speech Communication, 20, pp. 215-227, 1996 https://doi.org/10.1016/S0167-6393(96)00054-4
  10. R. Zelinski, 'A microphone array with adaptive post-filtering for noise reduction in reverberant rooms,' in Proc. IEEE International Conference on Acoustics, Speech and Signal Processing, vol. 5, pp. 2578-2581, 1988 https://doi.org/10.1109/ICASSP.1988.197172
  11. C. Marro, Y. Mahieux, and K. U. Simmer, 'Analysis of noise reduction and dereverberation techniques based on microphone arrays with postfiltering,' IEEE Trans. on Speech and Audio Processing, vol. 6, no. 3, May 1998 https://doi.org/10.1109/89.668818
  12. I. Cohen, 'Analysis of Two-Channel Generalized Sidelobe Canceller (GSC) With Post-Filtering,' IEEE Trans. Speech and Audio Processing, vol. 11, no. 6, November 2003 https://doi.org/10.1109/TSA.2003.818105
  13. S. Haykin, Communication Systems 4th ed., John Wiley & Sons, Inc., New York, USA., 2001
  14. M. Omologo and P. Svaizer, 'Acoustic Event Localization Using a Crosspower-spectrum Phase based Technique,' in Proc. IEEE International Conference on Acoustics, Speech and Signal Processing, vol. 2, pp. 273-276, 1994 https://doi.org/10.1109/ICASSP.1994.389667
  15. P. Vaidyanathan, Multirate Systems and Filter Banks, Englewood Cliffs, NJ: Prentice Hall, 1993
  16. L. J. Griffiths, C. W. Jim, 'An alternative approach to linearly constrained adaptive beamforming,' IEEE Trans. on Antennas Propagation, vol. 30, no. 1, pp. 27-34, Jan. 1982 https://doi.org/10.1109/TAP.1982.1142739