Speech decoder for decoding a speech signal using a bad frame masking unit for voiced frame and a bad frame masking unit for unvoiced frame

A speech decoder, comprising:

• a receiving unit for receiving and outputting input data, the input data including spectral data transmitted for each of a plurality of frames, delay of an adaptive codebook having a predetermined excitation signal corresponding to a pitch data, an index of excitation codebook constituting an excitation signal, gains of the adaptive and excitation codebooks and an amplitude of a speech signal;
• an error detection unit for checking whether an error of said each frame occurs based upon said corresponding input data having errors in perceptually important bits;
• a data memory for storing the input data after delaying the data by one frame;
• a speech decoder unit for decoding, when no error is detected by said error detection unit, the speech signal by using the spectral data, delay of the adaptive codebook having the predetermined excitation signal, index of the excitation codebook comprising the excitation signal, gains of the adaptive and excitation codebooks and the amplitude of the speech signal;
• a voiced/unvoiced frame judging unit for deriving a plurality of feature quantities from the speech signal that has been reproduced in said speech decoder unit in a previous frame and for checking whether a current frame is a voiced or unvoiced frame;
• a bad frame masking unit for voiced frame for interpolating, when an error is detected and the current frame is the voiced frame, the speech signal by using the data of the previous and current frames;
• and
• a bad frame masking unit for unvoiced frame for interpolating, when an error is detected and the current frame is the unvoiced frame, the speech signal by using data of the previous and current frames.

A speech decoder, comprising:

• a receiving unit configured to receive and output spectral data for each of a plurality of sequential frames, pitch information corresponding to a pitch period of said each sequential frame, index data of an excitation signal, and a gain, wherein each sequential frame has a fixed frame period, and wherein two of said sequential frames corresponds respectively to a current frame and a previous frame contiguous with said current frame;
• an error detecting unit connected to the receiving unit and configured to detect channel errors in predetermined bit positions of the input data that is output from the receiving unit;
• a data memory connected to the receiving unit and configured to delay and store the spectral data output from the receiving unit, the delay corresponding to the fixed frame period;
• a first switch connected to the error detecting unit and the receiving unit and configured to output the spectral data received from the receiving unit for the current frame along a first data path if the error detecting unit indicates an error in at least one of the predetermined bit positions of the spectral data of the current frame, the first switch configured to output the input data received from the receiving unit for the current frame along a second data path if the error detecting unit indicates no errors in any of the at least one of the predetermined bit positions of the spectral data of the current frame;
• a speech decoder unit configured to reproduce speech from data that is received from the first switch over the second data path;
• a voiced/unvoiced frame judging unit connected to the speech decoder unit and configured to derive, if the current frame has an error in at least of the predetermined bit positions, a plurality of feature quantities and to judge whether the current frame is a voiced frame or an unvoiced frame based on the feature quantities and a predetermined threshold value, the voiced/unvoiced frame judging unit configured to output a first judging signal as a result thereof;
• a second switch connected to the first switch via the first data path and connected to the voiced/unvoiced frame judging unit, the second switch configured to output data received from the first switch over the first data path to one of a third data path and a fourth data path in accordance with a state of the first judging signal;
• a bad frame masking unit for voiced frame connected to the second switch via the third data path and connected to the data memory, the bad frame masking unit configured to interpolate data received via the third data path from the second switch in accordance with the spectral data stored in the data memory;
• and
• a bad frame masking unit for unvoiced frame connected to the second switch via the fourth data path and connected to the data memory, the bad frame masking unit configured to interpolate data received via the fourth data path from the second switch in accordance with the spectral data stored in the data memory.