SIGNAL BAND WIDENING DEVICE, SIGNAL BAND WIDENING METHOD, AND PROGRAM THEREFOR

摘要

PROBLEM TO BE SOLVED: To stably generate a high-quality pseudo-wideband signal regardless of a communication correspondent.

SOLUTION: A signal band widening method includes the steps of: applying parallel bypass filtering to a narrowband signal using two different cutoff frequencies; calculating a power ratio between the post-filtering narrowband signals; determining a low-frequency enhancement level in accordance with the value of the ratio; subsequently calculating a modified gain factor from a gain factor for enhancing the low-frequency and the low-frequency enhancement level; multiplying the low-frequency enhancement level by the frequency-domain-converted narrowband signal to generate a low-frequency-enhanced frequency-domain signal; further duplicating a part of or the entire frequency-domain-converted narrowband signal to thereby generate a signal of a frequency band exceeding 4 kHz; combining the low-frequency-enhanced frequency-domain signal and the signal of a frequency band exceeding 4 kHz to generate a frequency domain wideband signal; and converting the signal into a temporal domain to generate a pseudo-wideband signal.

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