Method for reduction of aliasing introduced by spectral envelope adjustment in real-valued filterbanks

• US 8,606,587 B2
• Filed: 07/18/2012
• Issued: 12/10/2013
• Est. Priority Date: 09/18/2002
• Status: Expired due to Term

• Current Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Original Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Inventors: Kjorling, Kristofer, Villemoes, Lars
• Primary Examiner(s): Borsetti, Greg
• Application Number:
  US13/552,590
• Publication Number:
  US 20120284033A1
• Time in Patent Office: 510 Days
• Field of Search: 704/201, 704/203, 704/500, 704/E19.01, 704/E19.02
• US Class Current: 704/500
• CPC Class Codes: G10L 19/00 Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis in musical instruments G10H
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/025 Detection of transients or attacks for time/frequency resolution switching
• CPC Class Codes: G10L 19/083 the excitation function being an excitation gain G10L25/90 takes precedence
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 25/12 the extracted parameters being prediction coefficients
• CPC Class Codes: G10L 25/18 the extracted parameters being spectral information of each sub-band
• CPC Class Codes: G10L 25/21 the extracted parameters being power information
• CPC Class Codes: G10L 25/48 specially adapted for particular use
• CPC Class Codes: H03H 17/0266 Filter banks

Abstract

The present invention proposes a new method for improving the performance of a real-valued filterbank based spectral envelope adjuster. By adaptively locking the gain values for adjacent channels dependent on the sign of the channels, as defined in the application, reduced aliasing is achieved. Furthermore, the grouping of the channels during gain-calculation, gives an improved energy estimate of the real valued subband signals in the filterbank.

Claims

1. Method for reducing or eliminating intermodulation introduced by aliasing in a real-valued filterbank used for spectral envelope adjustment, comprising:

analysing an input signal to obtain information; and

using the obtained information to restrain envelope adjustment capabilities of the real-valued filterbank by grouping gain-values of adjacent channels, wherein the using comprises assessing which adjacent channels of the real-valued filterbank must have grouped gain-values, where the adjacent channels of the real-valued filterbank, which must have grouped gain-values, must not have independent gain-values.

2. The method of claim 1, further comprising altering a channel gain of adjacent channels between an analysis and a synthesis of the real-valued filterbank.

3. The method of claim 1, in which the using comprises performing a low-order linear prediction on subband samples of filterbank channels to assess, by observing the properties of an LPC polynomial derived by the low-order linear prediction, where in a filterbank channel a strong tonal component is present, wherein an order of the low-order linear prediction is equal to or smaller than a fifth order.

4. Non-transitory storage medium having stored thereon a computer program having a program code for performing the method in accordance with claim 1, when the computer program runs on a computer.

5. Apparatus for reducing or eliminating intermodulation introduced by aliasing in a real-valued filterbank used for spectral envelope adjustment, comprising:

an analyser configured for analysing an input signal to obtain information; and

a user configured for using the obtained information to restrain envelope adjustment capabilities of the real-valued filterbank by grouping gain-values of adjacent channels, wherein the user is configured to assess which adjacent channels of the real-valued filterbank must have grouped gain-values, where the adjacent channels of the real-valued filterbank, which must have grouped gain-values, must not have independent gain-values.