Post-processor, pre-processor, audio encoder, audio decoder and related methods for enhancing transient processing

Patent metadata

Field	Value
Publication number	US-11094331-B2
Application number	US-201916688938-A
Country	US
Kind code	B2
Filing date	Nov 19, 2019
Priority date	Feb 17, 2016
Publication date	Aug 17, 2021
Grant date	Aug 17, 2021

Abstract

An audio post-processor for post-processing an audio signal having a time-variable high frequency gain information as side information includes: a band extractor for extracting a high frequency band of the audio signal and a low frequency band of the audio signal; a high band processor for performing a time-variable modification of the high frequency band in accordance with the time-variable high frequency gain information to obtain a processed high frequency band; and a combiner for combining the processed high frequency band and the low frequency band. Furthermore, a pre-processor is illustrated.

First claim

The invention claimed is:

1. An audio pre-processor for pre-processing an audio signal, comprising:
a signal analyzer for analyzing the audio signal to determine a time-variable high frequency gain information;
a band extractor for extracting a high frequency band of the audio signal and a low frequency band of the audio signal;
a high band processor for performing a time-variable modification of the high frequency band in accordance with the time-variable high frequency gain information to acquire a processed high frequency band;
a combiner for combining the processed high frequency band and the low frequency band to acquire a pre-processed audio signal; and
an output interface for generating an output signal comprising the pre-processed audio signal and the time-variable high frequency gain information as side information;
wherein the signal analyzer is configured
to calculate a background measure for a background energy of the high frequency band for one or more time blocks neighboring in time placed before a current time block or placed subsequent to the current time block or placed before and subsequent to the current time block or comprising the current time block or excluding the current time block;
to calculate an energy measure for a high frequency band of the current block; and
to calculate a gain factor using the background measure and the energy measure based on the following equation:
wherein g float is a non-quantized gain factor, wherein k is a block index, wherein α is a variation influencing factor, wherein hp_bg_e[k] is the background measure of the high frequency band for a block k, wherein hp_e[k] is the energy measure of the high frequency band of the current block, wherein T quiet is a quiet threshold, and wherein the factor α and the quiet threshold are predetermined or controllable by additional control parameters.

2. The audio pre-processor of claim 1 ,
wherein the signal analyzer is configured to analyze the audio signal to determine a first characteristic in a first time block of the audio signal and a second characteristic in a second time block of the audio signal, the second characteristic being more transient than the first characteristic or being a larger high frequency energy level than the first characteristic,
wherein the signal analyzer is configured to determine a first gain information for the first characteristic and a second gain information for the second characteristic, and
wherein the high band processor is configured to apply a multiplicative factor to the high frequency band of the second time block in accordance with the second gain information stronger than the high frequency band of the first time block in accordance with the first gain information.

3. The audio pre-processor of claim 1 , wherein the signal analyzer is configured:
to calculate a background measure for a background energy of the high frequency band for one or more time blocks neighboring in time placed before a current time block or placed subsequent to the current time block or placed before and subsequent to the current time block or comprising the current time block or excluding the current time block;
to calculate an energy measure for a high band frequency of the current block; and
to calculate a gain factor using the background measure and the energy measure.

4. The audio pre-processor of claim 1 , wherein the signal analyzer and the high band processor are configured to calculate the time-variable high frequency gain information and to apply the time-variable high frequency gain information so that a variation of an energy of each block around a corresponding average energy of a background is reduced by at least 50% and advantageously by 75%.

5. The audio pre-processor of claim 1 ,
wherein the signal analyzer is configured to quantize and clip a raw sequence of gain information values to acquire the time-variable high frequency gain information as a sequence of quantized values,
wherein the high band processor is configured to perform the time-variable modification of the high frequency band in accordance with the sequence of quantized values, and
wherein the output interface is configured to introduce the sequence of quantized values into the side information as the time-variable high frequency gain information.

6. The audio pre-processor of claim 1 , in which the band extractor is configured to extract the low frequency band using a low pass filter device and to extract the high frequency band by subtracting the low frequency band from the audio signal.

7. The audio pre-processor in accordance with claim 1 , wherein the band extractor comprises:
an analysis windower for generating a sequence of blocks of sampling values of the audio signal using an analysis window, wherein the blocks are time-overlapping;
a discrete Fourier transform processor for generating a sequence of blocks of spectral values;
a low pass shaper for shaping each block of spectral values to acquire a sequence of low pass shaped blocks of spectral values;
a discrete Fourier inverse transform processor for generating a sequence of blocks of low pass time domain sampling values; and
a synthesis windower for windowing the sequence of blocks of low pass time domain sampling values using a synthesis window.

8. The audio pre-processor of claim 7 , wherein the block extractor further comprises:
an audio signal windower for windowing the audio signal using the analysis window and the synthesis window to acquire a sequence of windowed blocks of audio signal values, wherein the audio signal windower is synchronized with the windower so that the sequence of blocks of low pass time domain sampling values is synchronous with the sequence of windowed blocks of audio signal values.

9. The audio pre-processor of claim 7 ,
wherein the combiner is configured to perform a sample-wise addition of corresponding blocks of the sequence of blocks of low pass time domain sampling values and the sequence of modified blocks of high pass time domain sampling values to acquire a sequence of blocks of combination signal values.

10. The audio pre-processor of claim 9 , further comprising:
an overlap-add processor for calculating a pre-processed audio signal portion by adding audio samples of a first block of the sequence of combination signal values and audio samples of a neighboring second block adjacent to the first block in a block overlap range.

11. The audio pre-processor of claim 1 , wherein the analyzer additionally provides a control parameter computed by meta gain control, wherein the high band processor is configured to apply the time-variable modification also under consideration of the control parameter.

12. The audio pre-processor of claim 1 , wherein
wherein the band extractor, the high band processor and the combiner operate in overlapping blocks, wherein an overlap range is between 40% of the block length and 60% of the block length, or
wherein the block length is between 0.8 milliseconds and 5 milliseconds, or
wherein the time-variable modification performed by the high band processor is a multiplicative factor applied to each sample of a block in time domain.

13. The audio pre-processor of claim 1 ,
wherein an overlap range of the overlapping blocks is equal to one half of the earlier block and wherein a later block comprises the same length as the earlier block with respect to a number of sample values, and wherein the combiner comprises an overlap adder for performing the overlap add operation.

14. An audio encoding apparatus for encoding an audio signal, comprising:
the audio pre-processor of claim 1 , configured

Assignees

• Fraunhofer Ges Forschung

Inventors

• Ghido Florin
• Disch Sascha
• Herre Jürgen
• Adami Alexander
• Reutelhuber Franz

Classifications

• H03G3/00 Primary

  Gain control in amplifiers or frequency changers · CPC title

• H03G5/165

  Equalizers; Volume or gain control in limited frequency bands · CPC title

• G10L19/008

  Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing · CPC title

• G10L19/032 Primary

  Quantisation or dequantisation of spectral components · CPC title

• H03G5/005 Primary

  of digital signals · CPC title