Transient Audio Signal Processing for Time Stretching and Pitch Shift

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Solution Overview

Problem

Current audio signal processing systems, particularly those using digital techniques, face challenges in preserving the quality of transient events during time stretching, as existing methods often smear or impair the 'vertical coherence' of transients, leading to unnatural sound when trying to change the reproduction speed or pitch of audio signals.

Innovation Solution

An apparatus and method that replace transient signal portions with replacement signal portions adapted to the energy characteristics of non-transient signal portions, process the transient-reduced audio signal, and reinsert the transient content, using techniques like extrapolation and interpolation to maintain the spectral energy distribution and phase coherence.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If digital signal processing techniques are used to manipulate audio signals, then processing efficiency and control are improved, but transient events are smeared or distorted leading to unnatural sound and artifacts

Engineering Contradiction:

Improveprocessing efficiencyVSAvoidtransient preservation quality

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The audio signal is divided into multiple frequency bands using a filter bank, allowing different processing strategies to be applied to transient and non-transient components separately. This segmentation enables the system to process each band independently, preserving transient characteristics while maintaining overall processing efficiency.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different quality levels of processing are applied to different parts of the signal. Transient portions receive specialized processing that preserves their sharp characteristics, while non-transient portions receive standard processing. This local differentiation ensures high fidelity where needed without sacrificing overall processing efficiency.

Inventive Principle:

Principle #3Local quality

2Duration of action of moving object

If time stretching is applied to audio signals, then duration control is improved, but transient events are smeared across the entire region represented by the block

Engineering Contradiction:

Improvesignal duration controlVSAvoidtransient sharpness

Core Design Contradiction:

Duration of action of moving objectVSManufacturing precision

Solution Approach 1:

The signal is divided into frequency bands, and transients are identified and processed separately from the surrounding non-transient signal. This allows time stretching to be applied to the overall signal while transient regions maintain their temporal sharpness through separate processing paths.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Transient detection is performed before time stretching is applied. By identifying transient regions in advance, the system can apply different processing parameters to these regions, preventing the smearing effect that would otherwise occur during time stretching operations.

Inventive Principle:

Principle #10Preliminary action

3Speed

If pitch manipulation is applied to audio signals, then frequency control is improved, but transient events are distorted leading to artifacts

Engineering Contradiction:

Improvefrequency controlVSAvoidtransient fidelity

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

The audio signal is segmented into frequency bands, allowing pitch manipulation to be applied selectively. Transient components are identified and processed with different parameters than non-transient components, preserving transient fidelity while achieving the desired pitch control.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different processing quality levels are applied locally to transient and non-transient portions of the signal. This ensures that pitch manipulation achieves frequency control objectives while transient regions maintain their natural characteristics without distortion or artifacts.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS20120051549A1Apparatus, method and computer program for manipulating an audio signal comprising a transient event

Publication Date: 2012.03.01 FRAUNHOFER GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG EV

AI summary

An apparatus for manipulating an audio signal comprising a transient event has a transient signal replacer configured to replace a transient signal portion, comprising the transient event of the audio signal, with a replacement signal portion adapted to signal energy characteristics of one or more transient signal portions of the audio signal, or to signal energy characteristics of the transient signal portion, to obtain a transient-reduced audio signal. The apparatus also has a signal processor configured to process the transient-reduced audio signal to obtain a processed version of the transient-reduced audio signal. The apparatus also has a transient-signal-re-inserter configured to combine the processed version of the transient-reduced audio signal with a transient signal representing, in an original or processed form, a transient content of the transient signal portion.