| 摘要 |
PURPOSE: To provide a low bit rate vocoder in which a range of a reproduced voice is widened and tone can be improved. CONSTITUTION: An excitation signal generating device in a low bit rate vocoder calculates low frequency band energy value E included in a voice input signal in a low frequency band energy calculating means 10. A mixing ratio in which a pulse train signal and a white noise signal are mixed based on calculated low frequency band energy value E is obtained in a mixing ratio calculating means 12. An amplification factor of an amplifier 16 and a coefficient (a) of a first FIR filter 14 are switched based on this mixing ratio, and the pulse train signal and the white noise signal are added in an adder 20 with a desired mixing ratio. After normalization is performed in an amplifier 22 to adjust an effective value of a synthesized voice to an actual voice input signal, a final mixing excitation signal is outputted. Since an excitation signal is generated by mixing the white noise signal and the pulse train signal, tone of a reproduced voice can be improved. |
