A b s t r a c t : This paper describes an adaptive acoustic noise canceller (ANC), and its implementation on a digital signal processor. The system has a primary input f o r a noisy speech signal and a reference input f o r the noise.The reference input is adaptively filtered and subtracted from t h e primary input. Practical considerations a r e made, regarding the system implementation, the type and localization of the microphones used t o capture both the signal and the noise. Experimental results a r e presented, showing the system good behaviour when used in different practical environments.
The accurate estimation of the acoustical parameters of a space to be used by people, such as theaters, concert halls, conference rooms, sport stadiums, and other public areas, implies that the measurements should be evaluated in the presence of an audience. However, for reasons of annoyance, people are usually avoided and a correction factor related to the effective absorption of the audience area is applied to the results only. This procedure does not take into account the variability of some parameters such as the relative humidity during the event, which influences considerably the magnitude frequency response. The swept sine technique is very attractive in acoustical measurements due to the high signal-to-noise ratios (SNR) and robustness against nonlinearity of the measurement chain and time variance. The use of some convenient music tracks in agreement with the perceptual masking effect minimizes the annoyance and increases the SNR simultaneously. The sinusoidal synthesis algorithm is applied to some parts of the music. After questioning a set of persons, some results based on an annoyance indicator are presented giving advantages and disadvantages of this method.
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