Enhancing performance of spectral band replication and related high frequency reconstruction coding

• US 8,935,156 B2
• Filed: 04/15/2014
• Issued: 01/13/2015
• Est. Priority Date: 01/27/1999
• Status: Expired due to Fees

• Current Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Original Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Inventors: Liljeryd, Lars G., Kjoerling, Kristofer, Ekstrand, Per, Henn, Fredrik
• Primary Examiner(s): Armstrong, Angela A
• Application Number:
  US14/252,947
• Publication Number:
  US 20140229188A1
• Time in Patent Office: 273 Days
• Field of Search: 704/200.1, 704/219, 704/225, 704/501
• US Class Current: 704/200.1
• CPC Class Codes: G10L 19/028 Noise substitution, i.e. substituting non-tonal spectral components by noisy source comfort noise for discontinuous speech transmission G10L19/012
• CPC Class Codes: G10L 19/035 Scalar quantisation
• CPC Class Codes: G10L 19/06 Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 19/265 Pre-filtering, e.g. high frequency emphasis prior to encoding
• CPC Class Codes: G10L 21/038 using band spreading techniques
• CPC Class Codes: G10L 25/18 the extracted parameters being spectral information of each sub-band

Abstract

The present proposes new methods and an apparatus for enhancement of source coding systems utilizing high frequency reconstruction (HFR). It addresses the problem of insufficient noise contents in a reconstructed highband, by Adaptive Noise-floor Addition. It also introduces new methods for enhanced performance by means of limiting unwanted noise, interpolation and smoothing of envelope adjustment amplification factors. The present invention is applicable to both speech coding and natural audio coding systems.

Claims

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:

a device for adjusting a spectral envelope of the high-frequency reconstructed signal, wherein the device 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; and

a complex low delay filter bank for synthesizing an output audio signal from a combination of the decoded signal and the high-frequency reconstructed signal.

2. The apparatus in accordance with claim 1, in which the smoother is operative to perform the smoothing operation in time and frequency.

3. A method, implementable by a device, 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, the method comprising:

adjusting a spectral envelope of the high-frequency reconstructed signal, wherein the adjusting includes;

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; and

synthesizing, using a complex low delay filter bank, an output audio signal from a combination of the decoded signal and the high-frequency reconstructed signal.

4. The method in accordance with claim 3, in which the smoother is operative to perform the smoothing operation in time and frequency.

5. A non-transitory storage medium recording a program of instructions that is executable by a device for performing a method 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, the method comprising:

adjusting a spectral envelope of the high-frequency reconstructed signal, wherein the adjusting includes;

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; and

synthesizing, using a complex low delay filter bank, an output audio signal from a combination of the decoded signal and the high-frequency reconstructed signal.

6. The non-transitory storage medium of claim 5, in which the smoother is operative to perform the smoothing operation in time and frequency.