Dynamic range control and equalization of digital audio using warped processing

• US 20100010651A1
• Filed: 06/25/2009
• Published: 01/14/2010
• Est. Priority Date: 04/23/2004
• Status: Active Grant

• Current Assignee: Beijing Xiaomi Mobile Software Co., Ltd. (Xiaomi Corp.)
• Original Assignee: Jarmo Hiipakka, Ole Kirkeby
• Inventors: Hiipakka, Jarmo, Kirkeby, Ole
• Granted Patent: US 8,548,614 B2
• Time in Patent Office: Days
• US Class Current: 700/94
• CPC Class Codes: G10L 21/02 Speech enhancement, e.g. noise reduction or echo cancellation reducing echo effects in line transmission systems H04B3/20; echo suppression in hands-free telephones H04M9/08
• CPC Class Codes: G10L 21/0264 characterised by the type of parameter measurement, e.g. correlation techniques, zero crossing techniques or predictive techniques
• CPC Class Codes: H04L 25/03159 operating in the frequency domain H04L25/03165, H04L25/03178 take precedence

Abstract

This invention describes a method for adjusting the loudness and the spectral content of digital audio signals in a real-time using warped spectral filtering. A warped processing module modifies a spectral content of a digital audio signal with a set of gains for a plurality of non-linearly-scaled frequency bands determined by a warping factor λ of a warped delay line. Warped delay line signals, generated by the warped delay line, are processed by a warped filter block containing multiple warped finite impulse response filters, e.g., Mth band filters, using individual warped spectral filtering in said plurality of the non-linearly-scaled frequency bands, which is followed by a conventional processing by a dynamic range control/equalization block. The present invention describes another innovation, that is embedding the warped processing module in a two-channel quadrature mirror filter (QMF) bank for improving processing efficiency at high sample rates.

Claims

1. A warped processing module, comprising:

a warped delay line, responsive to a digital signal with a pre-selected sampling frequency, for providing N+1 warped delay line signals W₀, W₁, . . . W_N with a predetermined or a variable warping factor λ

determining a non-linear frequency scale factor for defining a plurality of non-linearly-scaled frequency bands within a frequency range corresponding to a half of said pre-selected sampling frequency, wherein N is an integer of at least a value of one;

a warped filter block, responsive to said N+1 warped delay line signals W₀, W₁, . . . W_N, configured to provide a warped filter block output signal based on warped spectral filtering of said N+1 warped delay line signals W₀, W₁, . . . W_N in said plurality of said non-linearly-scaled frequency bands, wherein a signal gain for each of the non-linearly-scaled frequency bands is set independently; and

a dynamic range control/equalization block, responsive to said warped filter block output signal, configured to provide a dynamic range control/equalization output signal, configured to provide a dynamic range control, an equalization, or both said dynamic range control and said equalization of said digital signal based on said warped filter block output signal,

wherein said warped filter block contains K Mth-band filters, wherein K is an integer of at least a value of one and each of said K Mth-band filters is responsive to said N+1 warped delay line signals W₀, W₁, . . . and wherein each of said K Mth-band filters is configured to provide a corresponding band output signal and said warped filter output signal comprises said K band output signals.

2. The warped processing module of claim 1, wherein said non-linearly-scaled frequency bands are defined on an approximately logarithmic frequency scale.

3. The warped processing module of claim 2, wherein said dynamic range control/equalization block contains K dynamic range control/equalization band blocks and each of said K dynamic range control/equalization band blocks is responsive to a corresponding one of said K band output signals and is configured to provide the dynamic range control, the equalization or both the dynamic range control and the equalization of said corresponding one of said K band output signals, and wherein each of said K dynamic range control/equalization band blocks is configured to provide a corresponding dynamic range control/equalization band output signal and said dynamic range control/equalization output signal comprises said K dynamic range control/equalization band output signal.

4. The warped processing module of claim 1, wherein said warped processing module is embedded between two-channel quadrature mirror filter analysis and synthesis blocks referred to as a two-channel quadrature mirror filter bank, wherein said analysis filter block is responsive to an audio input signal with a sampling frequency f_s and in a frequency range from 0 to f_s/2, and said analysis filter block is configured to provide said digital signal with a reduced sampling frequency f_sr=f_s/P which is equal to the pre-selected sampling frequency and in a low frequency branch, and to provide at least one complementary digital signal with the reduced sampling frequency f_sr=f_s/P and in a high frequency branch, wherein P>

1.

5. The warped processing module of claim 4, wherein said filter synthesis block is responsive to the dynamic range control/equalization output signal with the reduced sampling frequency f_sr=f_s/P and to said at least one complementary output signal with the reduced sampling frequency f_sr=f_s/P and configured to provide a digital audio output signal with the sampling frequency f_s in the corresponding frequency range from 0 to f_s/2.

6. The warped processing module of claim 5, wherein P=2 and wherein said filter analysis block is a two-channel quadrature mirror filter analysis block, said filter synthesis block is a two-channel quadrature mirror filter synthesis block, said at least one complementary input signal is a complementary input signal, said at least one complementary output signal is a complementary output signal, said low frequency branch is in a frequency range from 0 to f_s/4, said high frequency branch is in the frequency range from f_s/4 to f_s/2, and the filter bank is a two-channel quadrature mirror filter bank.

7. The warped processing module of claim 6, wherein the warped processing block is responsive to the digital signal and the warped processing said dynamic range control/equalization output signal using warped processing in said low frequency branch.

8. The warped processing module of claim 7, wherein said complementary digital signal is provided to a complementary module and the complementary module block is configured to generate said complementary output signal in said high frequency branch to match the processing in the low and the high frequency branches at a cross-over frequency f_s/4 which separates the low and the high frequency branches.

9. The warped processing module of claim 8, wherein said complementary module comprises:

a matching delay module, responsive to the complementary digital signal, configured to provide a matched delay signal to match a frequency-dependent delay of the low frequency branch due to said warped spectral filtering by the warped filter block at the cross-over frequency f_s/4; and

a variable gain block, responsive to said matched delay signal and to a high-band gain signal, configured to provide the complementary output signal to match a frequency-dependent gain of the low frequency branch due to said warped spectral filtering by the warped filter block at the cross-over frequency f_s/4.

10. The warped processing module of claim 9, wherein said high-band gain signal is a gain of a highest band of the plurality of said non-linearly-scaled frequency bands processed by the warped processing module and the dynamic range control/equalization block is configured to provide said high-band gain signal.

11. The warped processing module of claim 1, wherein said warped processing module is contained in a portable electronic device, an electronic communication device, a mobile electronic device or a mobile phone.

12. A method, comprising:

providing N+1 warped delay line signals W₀, W₁, . . . W_N with a predetermined or a variable warping factor λ

determining a non-linear frequency scale factor for defining a plurality of non-linearly-scaled frequency bands within a frequency range corresponding to a half of said pre-selected sampling frequency, said N+1 warped delay line signals W₀, W₁, . . . W_N are provided by a warped delay line of a warped processing module in response to a digital signal with a pre-selected sampling frequency;

providing a warped filter block output signal based on warped processing of said N+1 warped delay line signals W₀, W₁, . . . W_N in said plurality of said non-linearly-scaled frequency bands by a warped filter block of said warped processing module in response to said N+1 warped delay line signals W₀, W₁ . . . W_N, wherein a signal gain for each of the non-linearly-scaled frequency bands is set independently; and

providing a dynamic range control/equalization output signal in response to said warped filter block output signal by a dynamic range control/equalization block of said warped processing module for providing a dynamic range control, an equalization, or both said dynamic range control and said equalization of said digital signal,

wherein said warped filter block contains K Mth-band filters, wherein K is an integer of at least a value of one and each of said K Mth-band filters is responsive to said N+1 warped delay line signals W₀, W₁, . . . W_N and wherein each of said K Mth-band filters is configured to provide a corresponding band output signal and said warped filter output signal comprises said K band output signals.

13. The method of claim 12, wherein said non-linearly-scaled frequency bands are defined on a logarithmic frequency scale.

14. The method of claim 13, wherein said dynamic range control/equalization block contains K dynamic range control/equalization band blocks and each of said K dynamic range control/equalization band blocks is responsive to a corresponding one of said K band output signals and configured to provide the dynamic range control, the equalization or both the dynamic range control and the equalization of said corresponding one of said K band output signals, and wherein each of said K dynamic range control/equalization band blocks is configured to provide a corresponding dynamic range control/equalization band output signal and said dynamic range control/equalization output signal comprises said K dynamic range control/equalization band output signal.

15. The method of claim 12, wherein said warped processing module is embedded between two-channel quadrature mirror filter analysis and synthesis blocks referred to as a two-channel quadrature mirror filter bank, and wherein before the step of providing N+1 warped delay line signals W₀, W₁, . . . W_N, the method comprises:

providing by said two-channel quadrature mirror filter analysis block the digital signal with a reduced sampling frequency f_sr=f_s/2, which is equal to the pre-selected sampling frequency, and in a corresponding low frequency branch with a frequency range from 0 to f_s/2 in response to an audio input signal with a sampling frequency f_s and in a corresponding frequency range from 0 to f_s/2 and providing a complementary digital signal with the reduced sampling frequency f_sr=f_s/2 in a corresponding high frequency branch with the frequency range from f_s/4 to f_s/2 to a complementary module.

16. The method of claim 15, further comprising:

generating a complementary output signal in said high frequency branch by the complementary module to match processing in the low and the high frequency branches at a cross-over frequency f_s/4 which separates the low and the high frequency branches in response to said complementary digital signal and providing said complementary output signal to the two-channel quadrature mirror synthesis block;

providing to the two-channel quadrature mirror synthesis block said dynamic range control/equalization output signal with the reduced sampling frequency f_sr=f_s/2 generated by warped processing of the digital signal by the warped processing module; and

providing a digital audio output signal with the sampling frequency f_s and the corresponding frequency range from 0 to f_s/2 by the two-channel quadrature mirror synthesis block in response to said dynamic range control/equalization output signal and to said complementary output signal.

17. The method of claim 16, wherein said generating a complementary output signal comprises:

providing a matched delay signal to match a frequency-dependent delay of the low frequency branch due to said warped spectral filtering by the warped filter block at the cross-over frequency f_s/4 by a matching delay module of said complementary module in response to said complementary digital signal;

providing a high-band gain signal, which is a gain of a highest band of the plurality of said non-linearly-scaled frequency bands processed by the warped processing module, to a variable gain block of the complementary module by the a dynamic range control/equalization block; and

providing the complementary output signal by the variable gain block in response to said matched delay signal and to a high-band gain signal.