It is desirable that the measured acoustic impulse response has constant normalized noise power (NNP) in all frequency bands. However the conventional measurement signals aimed at achieving this property were derived intuitively, and the theoretical background is insufficient. In this work we first theoretically derived the relational formula that the measurement signals must satisfy for the measured impulse response to have constant NNP over all frequency bands. This formula includes all the measurement signals that achieve constant NNP. We then found the shortest (equivalently, the minimum energy) measurement signal among them. We call this signal the bandwise minimum noise (BMN) signal. Experiments to measure the room impulse responses were carried out. The experimental results confirmed that the impulse responses measured by the BMN signal had almost constant NNP in all frequency bands. Also, it was confirmed that the BMN signal achieved the required NNP for reverberation time measurement with the shortest signal length as compared with the conventional measurement signals.
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