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EP-4521400-B1 - APPARATUS FOR CONCEALING FRAME ERROR

EP4521400B1EP 4521400 B1EP4521400 B1EP 4521400B1EP-4521400-B1

Inventors

  • SUNG, HO-SANG
  • LEE, NAM-SUK

Dates

Publication Date
20260513
Application Date
20130610

Claims (5)

  1. A time domain frame error concealment, FEC, apparatus comprising: at least one processor configured to: check whether a current frame is either an error frame or a good frame, in a time domain signal; check whether a previous frame is either a burst error frame or a random error frame; select one mode from among a plurality of modes associated with smoothing, when the current frame is checked as an error frame, a good frame after a burst error frame or a good frame after a random error frame; and apply a different error concealment processing to the current frame, based on the selected mode, wherein the plurality of modes include a first mode when the current frame is an error frame, a second mode when the current frame is a good frame after a random error frame, and a third mode when the current frame is a good frame after a burst error frame.
  2. The apparatus of claim 1, the at least one processor further configured to perform frequency domain error concealment processing on the current frame when the current frame is checked as an error frame before time-frequency inverse transform processing.
  3. The apparatus of claim 1, wherein when the second mode is selected, the at least one processor is configured to apply a smoothing window between a signal of a previous frame and a signal of the current frame, and to perform overlap and add, OLA, processing, according to a smoothing process.
  4. The apparatus of claim 1, wherein when the third mode is selected, the at least one processor is configured to: copy a signal for overlap and add, OLA, processing of a next frame to a beginning part of the current frame according to a repeating process; perform smoothing on a signal of a previous frame and the copied signal to generate a replaced signal of the previous frame according to a first smoothing process; and perform smoothing on the replaced signal and a signal of the current frame according to a second smoothing process.
  5. The apparatus of claim 4, wherein when the third mode is selected, the at least one processor is configured to down-scale the current frame obtained by a result of the repeating process, according to a scaling process.

Description

Technical Field Exemplary Embodiments relate to frame error concealment, and more particularly, to a frame error concealment apparatus. Background Art When an encoded audio signal is transmitted over a wired/wireless network, if partial packets are damaged or distorted due to a transmission error, an error may occur in partial frames of a decoded audio signal. If the error is not properly corrected, sound quality of the decoded audio signal may be degraded in a duration including a frame in which the error has occurred (hereinafter, referred to as "error frame") and an adjacent frame. Regarding audio signal encoding, it is known that a method of performing time-frequency transform processing on a specific signal and then performing a compression process in a frequency domain provides good reconstructed sound quality. In the time-frequency transform processing, a modified discrete cosine transform (MDCT) is widely used. In this case, for audio signal decoding, the frequency domain signal is transformed to a time domain signal using inverse MDCT (IMDCT), and overlap and add (OLA) processing may be performed for the time domain signal. In the OLA processing, if an error occurs in a current frame, a next frame may also be influenced. In particular, a final time domain signal is generated by adding an aliasing component between a previous frame and a subsequent frame to an overlapping part in the time domain signal, and if an error occurs, an accurate aliasing component does not exist, and thus, noise may occur, thereby resulting in considerable deterioration of reconstructed sound quality. When an audio signal is encoded and decoded using the time-frequency transform processing, in a regression analysis method for obtaining a parameter of an error frame by regression-analyzing a parameter of a previous good frame (PGF) from among methods for concealing a frame error, concealment is possible by somewhat considering original energy for the error frame, but an error concealment efficiency may be degraded in a portion where a signal is gradually increasing or is severely fluctuated. In addition, the regression analysis method tends to cause an increase in complexity when the number of types of parameters to be applied increases. In a repetition method for restoring a signal in an error frame by repeatedly reproducing a PGF of the error frame, it may be difficult to minimize deterioration of reconstructed sound quality due to a characteristic of the OLA processing. An interpolation method for predicting a parameter of an error frame by interpolating parameters of a PGF and a next good frame (NGF) needs an additional delay of one frame, and thus, it is not proper to employ the interpolation method in a communication codec sensitive to a delay. Thus, when an audio signal is encoded and decoded using the time-frequency transform processing, there is a need of a method for concealing a frame error without an additional time delay or an excessive increase in complexity to minimize deterioration of reconstructed sound quality due to the frame error. US 2008/033718A1 discloses a classification-based frame loss concealment for audio signals. Disclosure Technical Problem Exemplary Embodiments provide a frame error concealment apparatus for concealing a frame error with low complexity without an additional time delay when an audio signal is encoded and decoded using the time-frequency transform processing. Exemplary Embodiments also provide an audio decoding apparatus for minimizing deterioration of reconstructed sound quality due to a frame error when an audio signal is encoded and decoded using the time-frequency transform processing. Exemplary Embodiments also provide an audio encoding apparatus for more accurately detecting information on a transient frame used for frame error concealment in an audio decoding apparatus. Technical Solution According to the present invention there is provided an apparatus as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows. Advantageous Effects According to exemplary embodiments, in audio encoding and decoding using time-frequency transform processing, when an error occurs in partial frames in a decoded audio signal, by performing error concealment processing in an optimal method according to a signal characteristic in the time domain, a rapid signal fluctuation due to an error frame in the decoded audio signal may be smoothed with low complexity without an additional delay. In particular, an error frame that is a transient frame or an error frame constituting a burst error may be more accurately reconstructed, and as a result, influence affected to a normal frame next to the error frame may be minimized. Description of Drawings FIGS. 1A and 1B are block diagrams of an audio encoding apparatus and an audio decoding apparatus according to an exemplary embodiment, respectively;FIGS. 2A and 2B are bl