Enhancing perceptual performance of SBR and related HFR coding methods by adaptive noise-floor addition and noise substitution limiting
Methods and an apparatus for enhancement of source coding systems utilizing high frequency reconstruction (HFR) are introduced. The problem of insufficient noise contents is addressed in a reconstructed highband, by using Adaptive Noise-floor Addition. New methods are also introduced for enhanced performance by means of limiting unwanted noise, interpolation and smoothing of envelope adjustment amplification factors. The methods and apparatus used are applicable to both speech coding and natural audio coding systems.
1. An apparatus for enhancing a source decoder, the source decoder generating a decoded signal by decoding an encoded signal obtained by source encoding of an original signal, the original signal having a low band portion and a high band portion, the encoded signal including the low band portion of the original signal and not including the high band portion of the original signal, wherein the decoded signal is used for high-frequency reconstruction to obtain a high-frequency reconstructed signal including a reconstructed high band portion of the original signal, comprising:
an adjuster for adjusting a spectral envelope of the high-frequency reconstructed signal, wherein the adjuster includes:
a smoother for smoothing envelope adjustment amplification factors to obtain smoothed envelope adjustment amplification factors for filter channels, the envelope adjustment amplification factors being calculated using scale factors of the high band portion of the original signal and corresponding scale factors of the high-frequency reconstructed signal; and
a multiplier for multiplying subband samples in filter channels using corresponding smoothed envelope adjustment factors to obtain the reconstructed high band portion of the original signal.
2. Apparatus in accordance with claim 1 , in which the smoother is operative to perform the smoothing operation in time and frequency.
3. A method of enhancing a source decoder, the source decoder generating a decoded signal by decoding an encoded signal obtained by source encoding of an original signal, the original signal having a low band portion and a high band portion, the encoded signal including the low band portion of the original signal and not including the high band portion of the original signal, wherein the decoded signal is used for high-frequency reconstruction to obtain a high-frequency reconstructed signal including a reconstructed high band portion of the original signal, comprising:
adjusting a spectral envelope of the high-frequency reconstructed signal, wherein the step of adjusting includes the following steps:
smoothing envelope adjustment amplification factors to obtain smoothed envelope adjustment amplification factors for filter channels, the envelope adjustment amplification factors being calculated using scale factors of the high band portion of the original signal and corresponding scale factors of the high-frequency reconstructed signal; and
multiplying subband samples in filter channels using corresponding smoothed envelope adjustment factors to obtain the reconstructed high band portion of the original signal.