Although an impulse response is the output from a linear system when excited by a pulse, such responses cannot be obtained with a high signal-to-noise ratio (SNR) because the pulse has low energy. Swept sine signals and maximum length sequences are alternative inputs, however, conventional signals still have low SNR problems in some frequency bands. This study is based on a swept-sine that maintains a constant SNR regardless of the frequency. The spectrum of a measurement signal is shaped, adapting to not only the background noise spectrum but also the recursively estimated transfer function of the system itself. To verify the validity of the proposed method, the authors measured the room impulse response in a noisy environment and calculated the room frequency response. The experimental result showed that a frequency response with an almost constant SNR was obtained with two iterations. This approach is useful in reverberation time measurements.
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