Detection of the fundamental frequency in noisy environment for speech enhancement of a hearing aid

This paper describes a method for noise-proof detection of the fundamental frequency of the voice in a noisy environment. Noise reduction techniques have been required in the development of a hearing aid, because noise makes intelligibility of hearing awfully inferior. In various methods of noise reduction, the fundamental frequency is often a significant parameter, but it is difficult to extract the frequency from the noisy voice. In order to utilize a comb filter method for noise reduction, a new method of detecting the fundamental frequency is developed by using the property of continuity in the fundamental frequency and the power spectrum envelope (PSE) of the human voice. The continuity of the PSE is utilized for determining the most reliable frequency. The gross pitch error (GPE) is reduced by the determination. Besides the frequency used for the comb filter is obtained from a linear predicting frequency and the latest fundamental frequency from the noisy voice, so as to suppress fluctuation of the frequency that degrades filtered voice. The procedure improves a fine pitch error (FPE) within 5%. The results of the evaluation showed that the present method proved to be superior to the traditional cepstrum method in the GPE and the FPE. We conclude that the proposed frequency detection method is available for noise reduction in the comb filter method.