Apparatus for improving packet loss, frame erasure, or jitter concealment
The invention presents a method to improve the recovering from packet loss, frame erasure or jitter concealment during signal communication, especially for VoIP (Voice Over Internet Protocol) applications. A variable delay concept (instead of constant delay) is introduced to guarantee the continuity and periodicity of signal after recovering lost frames, adding frames or removing frames. During the recovering of lost frames or the adding of extra frames, the copy of previous signal from history buffer into missing frame(s) is based on the frame length, onset, and offset information.
1. A method of significantly improving Packet Loss Concealment (PLC) or Frame Erasure Concealment (FEC) algorithm performance and maintaining signal periodicity in a decoder, the method comprising:
Receiving a current signal following a previously recovered signal;
Introducing a limited variable delay to the received current signal; and
Determining the limited variable delay by maximizing the correlation between the received current signal and the recovered signal, using the formula:
R
(
τ
)
=
Norm_Factor
·
∑
n
s
1
(
n
)
·
s
2
(
n
+
τ
)
wherein s 1 (n) is the recovered signal extended from a previous frame into a current frame, s 2 (n) is the received current signal in the current frame, τ is the variable delay which controls shifting of the received current signal, Norm_Factor is a normalization factor, and R(τ) is the correlation between the received current signal and the recovered signal.
2. The method of claim 1 , wherein Norm_Factor is defined as,
Norm_Factor
=
1
(
∑
n
s
1
(
n
)
·
s
1
(
n
)
)
·
(
∑
n
s
2
(
n
+
τ
)
·
s
2
(
n
+
τ
)
)
.
3. The method of claim 1 , wherein the recovered signal is obtained by using PLC or FEC algorithm which comprises a copy of previous signals from a history buffer into missing frame(s) and an Overlap Adds (OLA) of the copied signals.
4. The method of claim 1 , wherein the received current signal is obtained by decoding a normally or correctly received frame when the frame is not lost during a transmission.
5. The method of claim 1 further comprising the steps of:
Aligning the received current signal with the recovered signal;
And determining the variable delay while avoiding a too short or too long distance between two pitch peaks around the boundary of the recovered signal and the received current signal.