Whilst the seen and heard components of audio-visual events will be generated simultaneously, they regularly arrive at their receptor surfaces with significant physical asynchrony (e.g. when observer-event distance is relatively large [5]).
So, the high-frequency components (HFC) of audio signals are partly or completely discarded in many audio coding methods at low bit rates in order to increase coding efficiency.
Illusory percepts of audio-visual speech elements have been shown to occur in infants [18] [20] but these are weaker and more inconsistent than what is observed in adults, suggesting that experience with speech may be an important component of audio-visual speech perception [20].
To improve coding efficiency [1], a practical perceptual audio coding framework would encode and transmit only the low-frequency (LF) components of the audio.
For the frequency estimation of a real audio signal, the noise originates from other sound sources, environmental noise, and other frequency components of the audio signal.
After estimating the major components of an audio signal with sinusoidal model parameters (frequency, amplitude, and phase), the signal is reconstructed by the estimated components.
To make comparison in a uniform framework, the components of an audio signal are estimated in the same order by all of the algorithms.
These perceptual processes cover concepts such as, weighting the spectral components of the audio with the frequency response of the outer and middle ear, using masking models including hearing threshold, and forward and backward masking models.
In general, the major components of an audio signal are obtained by the following steps: firstly, finding the largest peak in the spectrum and estimating single-tone parameters from it; secondly, subtracting this estimated tone from the spectrum.
Among the methods to enhance the perceptual quality of the WB audio signals, blind bandwidth extension (BWE) is designed to analyze the statistical relationship between the low-frequency and high-frequency components of WB audio signals and artificially restore the missing high-frequency (HF) components in the frequency range of 7000~14,000 Hz from the decoded WB signals at the decoder end.
