Oversampling in a combined transposer filterbank

• US 10,584,386 B2
• Filed: 12/18/2018
• Issued: 03/10/2020
• Est. Priority Date: 10/21/2009
• Status: Active Grant

• Current Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Original Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Inventors: Villemoes, Lars, Ekstrand, Per
• Primary Examiner(s): Gauthier, Gerald
• Application Number:
  US16/223,112
• Publication Number:
  US 20190119753A1
• Time in Patent Office: 448 Days
• Field of Search: 341 51, 341 61, 375341, 375241, 375232, 381 17, 381 711, 381 942, 381 98, 381 66, 381 941, 381103, 381119, 381316, 381317, 382248, 382303, 4555501, 600300, 700 94, 702 76, 702189, 7042001, 704203, 704205, 704207, 704221, 704258, 704278, 704500, 704503, 704222, 704225, 708172, 708300, 708313, 712 4
• CPC Class Codes: C12Q 1/6883 for diseases caused by alterations of genetic material
• CPC Class Codes: C12Q 2600/118 Prognosis of disease development
• CPC Class Codes: C12Q 2600/156 Polymorphic or mutational markers
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 19/022 Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
• 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

Abstract

The present invention relates to coding of audio signals, and in particular to high frequency reconstruction methods including a frequency domain harmonic transposer. A system and method for generating a high frequency component of a signal from a low frequency component of the signal is described. The system comprises an analysis filter bank (501) comprising an analysis transformation unit (601) having a frequency resolution of Δf; and an analysis window (611) having a duration of D_A; the analysis filter bank (501) being configured to provide a set of analysis subband signals from the low frequency component of the signal; a nonlinear processing unit (502, 650) configured to determine a set of synthesis subband signals based on a portion of the set of analysis subband signals, wherein the portion of the set of analysis subband signals is phase shifted by a transposition order T; and a synthesis filter bank (504) comprising a synthesis transformation unit (602) having a frequency resolution of QΔf; and a synthesis window (612) having a duration of D_S; the synthesis filter bank (504) being configured to generate the high frequency component of the signal from the set of synthesis subband signals; wherein Q is a frequency resolution factor with Q≥1 and smaller than the transposition order T; and wherein the value of the product of the frequency resolution Δf and the duration D_A of the analysis filter bank is selected based on the frequency resolution factor Q.

Claims

1. A system for generating an output audio signal comprising a high frequency component from an input audio signal comprising a low frequency component using a transposition order T, comprising:

an analysis window unit configured to apply an analysis window of a length of L_A samples, thereby extracting a frame of the input signal;

an analysis transformation unit of order M and having a frequency resolution Δ

f configured to transform the L_A samples into M complex coefficients;

a nonlinear processing unit, configured to modify phases of the complex coefficients based on the transposition order T, and to modify magnitudes of the complex coefficients based on the transposition order T;

a synthesis transformation unit of order M and having a frequency resolution QΔ

f, configured to transform the altered coefficients into M altered samples;

wherein Q is a frequency resolution factor independent of the transposition order T; and

a synthesis window unit configured to apply a synthesis window of a length of L_s samples to the M altered samples, thereby generating a frame of the output signal;

wherein M is greater than L_A and is based on the frequency resolution factor Q.

2. A method for generating an output audio signal comprising a high frequency component from an input audio signal comprising a low frequency component using a transposition order T, the method comprising:

applying an analysis window of a length of L_A samples, thereby extracting a frame of the input signal;

transforming the frame of L_A samples of the input signal into M complex coefficients using an analysis transformation of order M and frequency resolution Δ

f;

modifying phases of the complex coefficients based on the transposition order T, and modifying magnitudes of the complex coefficients based on the transposition order T;

transforming the altered coefficients into M altered samples using a synthesis transformation of order M and frequency resolution QΔ

f;

wherein Q is a frequency resolution factor independent of the transposition order T; and

applying a synthesis window of a length of L_s samples to the M altered samples, thereby generating a frame of the output signal;

wherein M is greater than L_A and is based on the frequency resolution factor Q.

3. A non-transitory computer-readable storage medium comprising a sequence of instructions, wherein, when executed by one or more processors, the sequence of instructions causes the one or more processors to perform a method for generating an output audio signal comprising a high frequency component from an input audio signal comprising a low frequency component using a transposition order T, the method comprising:

applying an analysis window of a length of L_A samples, thereby extracting a frame of the input signal;

transforming the frame of L_A samples of the input signal into M complex coefficients using an analysis transformation of order M and frequency resolution Δ

f;

modifying phases of the complex coefficients by using the transposition order T, and modifying magnitudes of the complex coefficients based on the transposition order T;

transforming the altered coefficients into M altered samples using a synthesis transformation of order M and frequency resolution QΔ

f;

wherein Q is a frequency resolution factor independent of the transposition order T; and

applying a synthesis window of a length of L_s samples to the M altered samples, thereby generating a frame of the output signal;

wherein M is greater than L_A and is based on the frequency resolution factor Q.