Oversampling in a combined transposer filterbank

• US 10,186,280 B2
• Filed: 10/25/2017
• Issued: 01/22/2019
• 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:
  US15/792,956
• Publication Number:
  US 20180047411A1
• Time in Patent Office: 454 Days
• Field of Search: 370291, 370343, 375350, 37524001, 381 941, 381 98, 381 22, 700 94, 7042001, 704203, 704205, 704222, 704500, 704201, 704219, 704229, 704501, 704503, 708300, 455205, 702190
• 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 configured to generate a high frequency component of an audio signal from a low frequency component of the audio signal, comprising:

an analysis filter bank comprising an analysis transformation unit having a frequency resolution of Δ

f; and

an analysis window having a duration of D_A;

the analysis filter bank being configured to provide a set of analysis subband signals from the low frequency component of the signal;

a nonlinear processing unit configured to determine a set of synthesis subband signals based on a portion of the set of analysis subband signals, wherein phases of the portion of the set of analysis subband signals are modified based on a transposition order T, and wherein magnitudes of the portion of the set of analysis subband signals are modified based on the transposition order T; and

a synthesis filter bank comprising a synthesis transformation unit having a frequency resolution of QΔ

f; and

a synthesis window having a duration of D_S;

the synthesis filter bank 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 independent of the transposition order T; and

wherein the value of the product of the frequency resolution Δ

f and the duration D_A of the analysis filter bank equals the value of the product of the frequency resolution factor Q, the frequency resolution Δ

f and the duration D_S of the synthesis filter bank.

2. The system of claim 1, wherein the value of the product Δ

fD_A is proportional to

3. The system of claim 2, wherein the value of the product Δ

fD_A is smaller or equal to

4. The system of claim 1, wherein the value of the product Δ

fD_A is greater than

5. The system of claim 1, wherein

the analysis filter bank and the synthesis filter bank are evenly stacked such that a center frequency of an analysis subband is given by kΔ

f and a center frequency of a synthesis subband is given by nQΔ

f.

6. The system of claim 1, wherein

the analysis filter bank and the synthesis filter bank are oddly stacked such that a center frequency of an analysis subband is given by

7. A method for generating a high frequency component of an audio signal from a low frequency component of the audio signal, the method comprising:

providing a set of analysis subband signals from the low frequency component of the signal using an analysis filter bank comprising an analysis transformation unit having a frequency resolution of Δ

f and an analysis window having a duration of D_A;

determining a set of synthesis subband signals based on a portion of the set of analysis subband signals, wherein phases of the portion of the set of analysis subband signals are modified based on a transposition order T, and wherein magnitudes of the portion of the set of analysis subband signals are modified based on the transposition order T; and

generating the high frequency component of the signal from the set of synthesis subband signals using a synthesis filter bank comprising a synthesis transformation unit having a frequency resolution of QΔ

f and a synthesis window having a duration of D_S;

wherein Q is a resolution factor with Q≥

1 and independent of the transposition order T; and

wherein the value of the product of the frequency resolution Δ

f and the duration D_A of the analysis filter bank equals the value of the product of the frequency resolution factor Q, the frequency resolution Δ

f and the duration D_S of the synthesis filter bank.

8. 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 a high frequency component of an audio signal from a low frequency component of the audio signal, the method comprising:

providing a set of analysis subband signals from the low frequency component of the signal using an analysis filter bank comprising an analysis transformation unit having a frequency resolution of Δ

f and an analysis window having a duration of D_A;

determining a set of synthesis subband signals based on a portion of the set of analysis subband signals, wherein phases of the portion of the set of analysis subband signals are modified based on a transposition order T, and wherein magnitudes of the portion of the set of analysis subband signals are modified based on the transposition order T; and

generating the high frequency component of the signal from the set of synthesis subband signals using a synthesis filter bank comprising a synthesis transformation unit having a frequency resolution of QΔ

f and a synthesis window having a duration of D_S;

wherein Q is a resolution factor with Q≥

1 and independent of the transposition order T; and

wherein the value of the product of the frequency resolution Δ

f and the duration D_A of the analysis filter bank equals the value of the product of the frequency resolution factor Q, the frequency resolution Δ

f and the duration D_S of the synthesis filter bank.