Method and Apparatus for Frame Loss Concealment in Transform Domain

An apparatus for compensating for a lost frame in a transform domain, comprising processor for performing instructions stored in a non-transitory computer readable medium to execute steps in following units:

• a frequency-domain coefficient calculation unit, a transform unit, and a waveform adjustment unit, wherein,
• the frequency-domain coefficient calculation unit is configured to calculate frequency-domain coefficients of a current lost frame using frequency-domain coefficients of one or more frames prior to the current lost frame;
• the transform unit is configured to obtain an initially compensated signal of the current lost frame by performing frequency-time transform on the frequency-domain coefficients of the current lost frame calculated by the frequency-domain coefficient calculation unit;
• and
• the waveform adjustment unit is configured to obtain an estimated pitch period value by estimating a pitch period of the current lost frame, and to obtain a compensated signal of the current lost frame by judging whether the estimated pitch period value is usable, and if the pitch period value is unusable, use the initially compensated signal of the current lost frame as the compensated signal of the current lost frame;
• and if the pitch period value is usable, obtain the compensated signal of the current lost frame by performing waveform adjustment on the initially compensated signal with a time-domain signal of the frame prior to the current lost frame;
• wherein, the waveform adjustment unit comprises an adjustment sub-unit, wherein,
• the adjustment sub-unit is configured to:
• supposing that the current lost frame is an xth lost frame, wherein x>0, and when x is larger than k (k>0), take the initially compensated signal of the current lost frame as the compensated signal of the current lost frame, otherwise, perform the following steps;
• establishing a buffer with a length of L, wherein L is a frame length;
• when x equals 1, configuring the first L1 samples of the buffer as a first L1-length signal of the initially compensated signal of the current lost frame, wherein L1>0;
• when x equals 1, concatenating the last pitch period of time-domain signal of the frame prior to the current lost frame and the first L1-length signal in the buffer, repeatedly copying the concatenated signal into the buffer, until the buffer is filled up to obtain a time-domain signal with a length of L, and during each copy, if the length of the existing signal in the buffer is l, copying the signal to locations from l−L1 to l+T−1 of the buffer, wherein l>0, T is a pitch period value, and for the resultant overlapped area with a length of L1, the signal of the overlapped area is obtained by adding signals of two overlapping parts after windowing respectively;
• when x is larger than 1, repeatedly copying the last pitch period of compensated signal of the frame prior to the current lost frame into the buffer without overlapping, until the buffer is filled up to obtain a time-domain signal with a length of L;
• when x is less than k, taking the signal in the buffer as the compensated signal of the current lost frame;
• when x equals k, performing overlap-add on the signal in the buffer and the initially compensated signal of the current lost frame, and taking the obtained signal as the compensated signal of the current lost frame,
• for a first correctly received frame after the current lost frame, if a number of consecutively loss frames is less than k, establishing a buffer with a length of L, repeatedly copying the last pitch period of compensated signal of the frame prior to the first correctly received frame into the buffer without overlapping until the buffer is filled up, performing overlap-add on the signal in the buffer and a time-domain signal obtained by decoding the first correctly received frame, and taking the obtained signal as a time-domain signal of the first correctly received frame.