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Aliasing reduction using complex-exponential modulated filterbanks

A filter bank, digital filter technology, applied in the network using time-varying components, digital technology network, adaptive network and other directions, can solve the problem of output signal aliasing unnatural signal and so on

Inactive Publication Date: 2004-05-19
DOLBY INT AB
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, any attempt to modify subband samples or spectral coefficients by applying equalization gain curves or quantized sampling results in severe aliasing artifacts in the output signal

Method used

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  • Aliasing reduction using complex-exponential modulated filterbanks
  • Aliasing reduction using complex-exponential modulated filterbanks
  • Aliasing reduction using complex-exponential modulated filterbanks

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Experimental program
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Embodiment Construction

[0020] It should be understood that the invention is applicable to a range of implementations incorporating digital filter banks other than those explicitly mentioned in this patent.

[0021] digital filter bank

[0022] A digital filter bank is a collection of two or more parallel digital filters sharing a common input or a common output ["Multirate Systems and Filter Banks" P.P. Vaidyanathan Prentice Hall: Englewood Cliffs, NJ, 1993]. When a common input is shared, the filterbank is called an analysis filterbank. The analysis group splits the input signal into M independent signals called subband signals. The analysis filter is denoted as H k (z), where k=0...M-1. The analysis filter is critically sampled (or top sampled) when the sampling factor of the subband signal is M. The total number of subband samples per unit time is equal to the number of samples of the input signal per unit time. The combining group combines these subband signals into a common output signal...

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Abstract

The present invention proposes a new method and apparatus for the improvement of digital filterbanks, by a complex extension of cosine-modulated digital filterbanks. The invention employs complex-exponential-modulation of a low-pass prototype filter and new methods for optimizing the characteristics of this filter. The invention substantially reduces artifacts due to aliasing emerging from independent modifications of subband signals, for example when using a filterbank as an spectral equalizer. The invention is preferably implemented in software, running on a standard PC or a digital signal processor (DSP), but can also be hardcoded on a custom chip. The invention offers essential improvements for various types of digital equalizers, adaptive filters, multiband companders and spectral envelope adjusting filterbanks used in high frequency reconstruction (HFR) systems.

Description

technical field [0001] The present invention relates to the field of subsampled digital filter banks and provides a method and apparatus for substantially reducing losses arising from modifying, eg quantization or attenuation, the spectral coefficients or subband signals of a digital filter bank. The present invention can be applied to digital equalizers ["Efficient 20-band digital audio equalizer" A.J.S.Ferreira, J.M.N.Viera, AES preprint, 98 th Convention 1995 February 25-28 Paris, N.Y., USA], Adaptive Filters ["Subband Adaptive Filtering with Critical Sampling: Analysis, Experimentation and Application to Echo Cancellation" A.Gilloire, M.Vetterli, IEEE Transactions on Signal Processing , vol.40, no.8, August, 1992], multiband signal companders, and audio coding systems using high frequency reproduction (HFR), in which digital filter banks are used for spectral envelope adaptation Adjustment, such as Spectrum Band Replication (SBR) system [WO98 / 57436]. Background techniq...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G10L25/00G10L25/18H03H17/02H03H21/00H03M7/30
CPCH03H17/0266H03H19/00
Inventor 佩尔·埃克斯特兰德
Owner DOLBY INT AB
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