High-Frequency Envelope Processing for Audio Transient Pre-Echo

Solution Overview

Problem

Existing audio processing technologies face challenges in encoding transient signals like applause and percussive sounds due to pre-echo artifacts, which are difficult to manage with current perceptual coding methods, especially at low bit-rates, leading to reduced audio quality.

Innovation Solution

The implementation of High Resolution Envelope Processing (HREP) which involves pre-processing the audio signal to flatten high-frequency transient events and post-processing to shape them back, using time-variable gain information to reduce short-time dynamics and improve encoding efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of information

If classic filterbank based perceptual coders are used to exploit simultaneous masking, then spectral coding efficiency is improved, but pre-echo artifacts occur due to temporal spreading of quantization noise

Engineering Contradiction:

Improvespectral coding efficiencyVSAvoidpre-echo artifacts

Core Design Contradiction:

Loss of informationVSObject-affected harmful factors

Solution Approach 1:

The patent applies temporal noise shaping as a preliminary action before spectral coding to pre-distribute quantization noise in the time domain according to temporal masking thresholds. This preliminary temporal arrangement prevents pre-echo artifacts from occurring after spectral transformation, while maintaining the spectral coding efficiency of filterbank-based perceptual coders.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the temporal distribution parameter of quantization noise by applying temporal noise shaping filters that modify the noise characteristics in the time domain. This parameter change allows the noise to follow temporal masking thresholds, preventing pre-echo artifacts while preserving spectral coding performance.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If quantization is applied in the spectral domain, then spectral precision is improved, but quantization noise spreads out in time exceeding original signal components

Engineering Contradiction:

Improvespectral precisionVSAvoidtemporal signal integrity

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent applies temporal noise shaping as a preliminary action before spectral quantization to pre-distribute quantization noise in the time domain according to temporal masking thresholds. This preliminary temporal arrangement prevents pre-echo artifacts from occurring after spectral transformation, while maintaining the spectral coding efficiency of filterbank-based perceptual coders.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the temporal distribution parameter of quantization noise by applying temporal noise shaping filters that modify the noise characteristics in the time domain. This parameter change allows the noise to follow temporal masking thresholds, preventing pre-echo artifacts while preserving spectral coding performance.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If long analysis filterbank windows are used, then spectral resolution is improved, but temporal spreading of quantization noise increases

Engineering Contradiction:

Improvespectral resolutionVSAvoidtemporal spreading duration

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent applies temporal noise shaping as a preliminary action before spectral coding to pre-distribute quantization noise in the time domain according to temporal masking thresholds. This preliminary temporal arrangement prevents pre-echo artifacts from occurring after spectral transformation, while maintaining the spectral coding efficiency of filterbank-based perceptual coders.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS20240347067A1Post-processor, pre-processor, audio encoder, audio decoder and related methods for enhancing transient processing

Publication Date: 2024.10.17 FRAUNHOFER GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG EV

AI summary

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.