Enhancing perceptual performance of SBR and related HFR coding methods by adaptive noise-floor addition and noise substitution limiting

• US 8,036,882 B2
• Filed: 06/24/2009
• Issued: 10/11/2011
• Est. Priority Date: 01/27/1999
• Status: Active Grant

• Current Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Original Assignee: Coding Technologies Sweden AB
• Inventors: Liljeryd, Lars G., Kjoerling, Kristofer, Ekstrand, Per, Henn, Fredrik
• Primary Examiner(s): Armstrong; Angela A
• Application Number:
  US12/491,001
• Publication Number:
  US 20090319280A1
• Time in Patent Office: 839 Days
• Field of Search: 704/200, 704/200.1, 704/219, 704/225, 704500-504
• 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

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.

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:

an interpolator for interpolating spectral envelope data, the spectral envelope data including a scale factor for a group of filterbank channels, the group having a plurality of filterbank channels, to obtain an interpolated scale factor for each filterbank channel in the group of filterbank channels;

a transposer for generating the high-frequency reconstructed signal using the decoded signal;

an analyzer for analyzing the high-frequency reconstructed signal to obtain a scale factor for each filterbank channel in the group of filterbank channels;

an amplification factor calculator for calculating an amplification factor for each filterbank channel in the group using the scale factors and the interpolated scale factors; and

an adjuster for adjusting a spectral envelope of the high-frequency reconstructed signal using the amplification factors for the channels in the group.

2. Apparatus in accordance with claim 1, in which the interpolator is operative to assign the scale factor for a group of channels to each channel in the group.

3. Apparatus in accordance with claim 1, in which the adjuster is operative to limit or smooth calculated amplification factors.

4. 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:

interpolating spectral envelope data, the spectral envelope data including a scale factor for a group of filterbank channels, the group having a plurality of filterbank channels, to obtain an interpolated scale factor for each filterbank channel in the group of filterbank channels;

generating the high-frequency reconstructed signal using the decoded signal;

analyzing the high-frequency reconstructed signal to obtain a scale factor for each filterbank channel in the group of filterbank channels;

calculating an amplification factor for each filterbank channel in the group using the scale factors and the interpolated scale factors; and

adjusting a spectral envelope of the high-frequency reconstructed signal using the amplification factors for the channels in the group.