Voice encoding method and apparatus

A speech coding method of selecting an excitation mode from a plurality of excitation modes, and encoding an input speech frame by frame with a predetermined length by using the excitation mode selected, said speech coding method comprising the steps of:

• encoding in the respective excitation modes a target signal to be encoded that is obtained from the input speech, and outputting coding distortions involved in the encoding;
• selecting one of the excitation modes in response to a compared result obtained by comparing the coding distortions involved in the encoding;
• comparing the coding distortion corresponding to the excitation mode selected at the step of selecting with one of three threshold values consisting of a fixed threshold value, a threshold value that is determined in response to signal power of the input speech and a threshold value that is determined in response to signal power of the target signal to be encoded;
• and
• replacing the excitation mode selected at the step of selecting, in response to a compared result obtained at the step of comparing.

A speech coding apparatus that selects an excitation mode from a plurality of excitation modes, and encodes an input speech frame by frame with a predetermined length by using the excitation mode selected, said speech coding apparatus comprising:

• coding units for encoding in the respective excitation modes a target signal to be encoded that is obtained from the input speech, and outputting coding distortions involved in the encoding;
• a comparator for comparing at least one of the coding distortions involved in the encoding with one of three threshold values consisting of a fixed threshold value, a threshold value that is determined in response to signal power of the input speech and a threshold value that is determined in response to signal power of the target signal to be encoded;
• and
• a selecting unit for selecting the excitation mode in response to the coding distortions involved in the encoding by said coding units and a compared result of said comparator.

A speech coding apparatus for selecting an excitation mode from a plurality of excitation modes, and encoding an input speech frame by frame with a predetermined length by using the excitation mode selected, said speech coding apparatus comprising:

• coding units for encoding in the respective excitation modes a target signal to be encoded that is obtained from the input speech, and outputting coding distortions involved in the encoding;
• a selecting unit for comparing the coding distortions involved in the encoding by said coding units, and for selecting one of the excitation modes in response to a compared result obtained;
• a comparator for comparing the coding distortion corresponding to the excitation mode selected by said selecting unit with one of three threshold values consisting of a fixed threshold value, a threshold value that is determined in response to signal power of the input speech and a threshold value that is determined in response to signal power of the target signal to be encoded;
• and
• a substituting unit for replacing the excitation mode selected by said selecting unit, in response to a compared result of said comparator.