Efficient combined harmonic transposition

• US 9,881,597 B2
• Filed: 10/14/2015
• Issued: 01/30/2018
• Est. Priority Date: 05/27/2009
• Status: Active Grant

• Current Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Original Assignee: Dolby International AB (Dolby Laboratories Incorporated)
• Inventors: Ekstrand, Per, Villemoes, Lars, Hedelin, Per
• Primary Examiner(s): Vo, Huyen
• Application Number:
  US14/882,559
• Publication Number:
  US 20160035329A1
• Time in Patent Office: 839 Days
• Field of Search: 704500-504, 704220-226
• CPC Class Codes: G10H 1/0091 Means for obtaining special acoustic effects combined with modulation G10H1/043
• CPC Class Codes: G10H 1/125 using a digital filter
• CPC Class Codes: G10H 2210/311 Distortion, i.e. desired non-linear audio processing to change the tone colour, e.g. by adding harmonics or deliberately distorting the amplitude of an audio waveform
• 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 21/0388 Details of processing therefor

Abstract

The present document relates to audio coding systems which make use of a harmonic transposition method for high frequency reconstruction (HFR), and to digital effect processors, e.g. so-called exciters, where generation of harmonic distortion adds brightness to the processed signal. In particular, a system configured to generate a high frequency component of a signal from a low frequency component of the signal is described. The system may comprise an analysis filter bank (501) configured to provide a set of analysis subband signals from the low frequency component of the signal; wherein the set of analysis subband signals comprises at least two analysis subband signals; wherein the analysis filter bank (501) has a frequency resolution of Δf. The system further comprises a nonlinear processing unit (502) configured to determine a set of synthesis subband signals from the set of analysis subband signals using a transposition order P; wherein the set of synthesis subband signals comprises a portion of the set of analysis subband signals phase shifted by an amount derived from the transposition order P; and a synthesis filter bank (504) configured to generate the high frequency component of the signal from the set of synthesis subband signals; wherein the synthesis filter bank (504) has a frequency resolution of FΔf; with F being a resolution factor, with F≧1; wherein the transposition order P is different from the resolution factor F.

Claims

1. A system configured to generate a high frequency component of a signal from a low frequency component of the signal, the system comprising:

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

wherein the analysis filter bank has a frequency resolution of Δ

f;

a first nonlinear processing unit configured to determine a first set of synthesis subband signals having a frequency resolution of FΔ

f, with F being a resolution factor, with F≧

1 from the set of analysis subband signals using a first transposition order P₁;

a second nonlinear processing unit configured to determine a second set of synthesis subband signals having the frequency resolution of FΔ

f from the set of analysis subband signals using a second transposition order P₂;

wherein the second nonlinear processing unit is configured to determine at least one subband signal of the second set of synthesis subband signals by interpoling between two intermediate synthesis subband signals having a frequency resolution of P₂Δ

f;

a combining unit configured to combine the first and the second set of synthesis subband signals;

thereby yielding a combined set of synthesis subband signals; and

a synthesis filter bank configured to generate the high frequency component of the signal from the combined set of synthesis subband signals;

wherein the synthesis filter bank has a frequency resolution of FΔ

f.

2. The system of claim 1, wherein

the analysis filter bank has a number L_A of analysis subbands, with L_A>

1, where k is an analysis subband index with k=0, . . . ,L_A−

1; and

the synthesis filter bank has a number L_Sof synthesis subbands, with L_S>

0, where n is a synthesis subband index with n=0, . . . , L_S−

1.

3. The system of claim 2, wherein the number L_A of analysis subbands is equal to the number L_S of synthesis subbands.

4. The system of claim 2, wherein the first and/or second nonlinear processing units are configured to determine an n^th synthesis subband signal of the first and/or second set of synthesis subband signals from a k^th analysis subband signal and a (k+1)^th analysis subband signal of the set of analysis subband signals.

5. The system of claim 4, wherein the second nonlinear processing unit is configured to

determine a phase of the n^th synthesis subband signal as the sum of a shifted phase of the k^th analysis subband signal and a shifted phase of the (k+1)^th analysis subband signal;

and/or

determine a magnitude of the n^th synthesis subband signal as the product of an exponentiated magnitude of the k^th analysis subband signal and an exponentiated magnitude of the (k+1)^th analysis subband signal.

6. The system of claim 5, wherein

the analysis subband index k of the analysis subband signal contributing to the synthesis subband with synthesis subband index n is given by the integer obtained by truncating the expression

7. The system of claim 6, wherein the second nonlinear processing unit is configured to

determine the phase of the n^th synthesis subband signal as the sum of the phase of the k^th analysis subband signal multiplied by P₂(1−

r) and the phase of the (k+1)^th analysis subband signal multiplied by P₂r; and

/or

determine the magnitude of the n^th synthesis subband signal as the product of the magnitude of the k^th analysis subband signal raised to the power of (1−

r) and the magnitude of the (k+1)^th analysis subband signal raised to the power of r.

8. The system of claim 1, wherein the first nonlinear processing unit is configured to

determine a first set of intermediate synthesis subband signals having a frequency resolution of P₁Δ

f; and

interpolate one or more intermediate synthesis subband signals to determine the synthesis subband signal of the first set of synthesis subband signals having a frequency resolution of FΔ

f.

9. The system of claim 1, wherein the first transposition order P₁ and the second transposition order P₂ are different.

10. The system of claim 1, wherein

the first set of synthesis subband signals is determined based on a portion of the set of analysis subband signals phase shifted by an amount derived from the first transposition order P₁;

and/or

the second set of synthesis subband signals is determined based on a portion of the set of analysis subband signals phase shifted by an amount derived from the second transposition order P₂.

11. The system of claim 1, wherein

the combining unit is configured to superpose synthesis subband signals of the first and the second set of synthesis subband signals corresponding to overlapping frequency ranges.

12. The system of claim 1, further comprising:

an analysis quadrature mirror filter bank, referred to as QMF bank, configured to convert an audio signal into a plurality of QMF subband signals;

wherein the low frequency component corresponds to at least one of the plurality of QMF subband signals.

13. The system of claim 1, wherein the first nonlinear processing unit is configured to determine a synthesis subband signal of the first set of synthesis subband signals based on

an analysis subband signal of the set of analysis subband signals phase shifted by the transposition order P₁;

or

a pair of analysis subband signals from the set of analysis subband signals wherein a first member of the pair of analysis subband signals is phase shifted by a factor P′ and

a second member of the pair is phase shifted by a factor P″

, with P′

+P″

=P₁.

14. 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 nFΔ

f.

17. The system of claim 1, wherein the first nonlinear processing unit is configured to determine a synthesis subband signal of the first set of synthesis subband signals based on an analysis subband signal of the set of analysis subband signals phase multiplied by the transposition order P₁.

18. The system of claim 1, wherein the first nonlinear processing unit is configured to determine a synthesis subband signal of the first set of synthesis subband signals based on a pair of analysis subband signals from the set of analysis subband signals wherein a first member of the pair of analysis subband signals is phase multiplied by a factor P′

and a second member of the pair is phase multiplied by a factor P″

, with P′

+P″

=P₁.

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

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

f;

determining a first set of synthesis subband signals having a frequency resolution of FΔ

f, with F being a resolution factor, with F≧

1 from the set of analysis subband signals using a first transposition order P₁;

determining a second set of synthesis subband signals having the frequency resolution of FΔ

f from the set of analysis subband signals using a second transposition order P₂;

wherein determining a second set of synthesis subband signals comprises determining at least one subband signal of the second set of synthesis subband signals by interpolating between two intermediate synthesis subband signals having a frequency resolution of P₂Δ

f;

combining the first and the second set of synthesis subband signals to yield a combined set of synthesis subband signals; and

generating the high frequency component of the signal from the combined set of synthesis subband signals using a synthesis filter bank having a frequency resolution of FΔ

f.

16. A non-transitory computer-readable medium comprising executable instructions for performing the method of claim 15 when executed on a computer.