Audio Coding with Periodic Combined Envelopes for Pitch Peaks

Solution Overview

Problem

Existing audio signal coding methods using linear predictive coefficients for spectral envelopes result in low approximation accuracy around peaks caused by the pitch period, leading to inefficient variable-length coding.

Innovation Solution

The encoder and decoder employ a periodic combined envelope sequence generation device that transforms amplitude spectral envelopes into periodic combined envelope sequences, providing high approximation accuracy around pitch period peaks using a small code amount by incorporating a periodic component analysis.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If linear predictive coefficients are used to obtain spectral envelope, then code amount is reduced, but approximation accuracy around pitch period peaks deteriorates

Engineering Contradiction:

Improvecode amountVSAvoidapproximation accuracy around pitch period peaks

Core Design Contradiction:

Quantity of substanceVSMeasurement precision

Solution Approach 1:

The patent merges two types of spectral envelopes: the amplitude spectral envelope obtained from linear predictive coefficients and a periodic spectral envelope generated based on pitch period information. By combining these envelopes through multiplication or addition, the invention achieves both compact coding (using small code amounts for the linear predictive parameters) and high approximation accuracy (by incorporating periodic structure information at pitch period peaks)

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The invention creates a composite spectral envelope that combines characteristics of different envelope types. The amplitude spectral envelope provides overall spectral shape while the periodic spectral envelope enhances peak structures at pitch periods, creating a composite representation that achieves high accuracy with efficient coding

Inventive Principle:

Principle #40Composite materials

2Productivity

If linear predictive coefficients are used for spectral envelope, then coding efficiency is improved through small code amount, but accuracy at pitch period peaks deteriorates

Engineering Contradiction:

Improvecoding efficiencyVSAvoidaccuracy at pitch period peaks

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent merges two types of spectral envelopes: the amplitude spectral envelope obtained from linear predictive coefficients and a periodic spectral envelope generated based on pitch period information. By combining these envelopes through multiplication or addition, the invention achieves both compact coding (using small code amounts for the linear predictive parameters) and high approximation accuracy (by incorporating periodic structure information at pitch period peaks)

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentEP3696812B1Encoder, decoder, coding method, decoding method, coding program, decoding program and recording medium

Publication Date: 2021.06.09 NIPPON TELEGRAPH & TELEPHONE CORP

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AI summary

An encoder of the present invention comprises a periodic-combined-envelope generating part and a variable-length coding part. The periodic-combined-envelope generating part generates a periodic combined envelope sequence which is a frequency-domain sequence based on a spectral envelope sequence which is a frequency-domain sequence corresponding to a linear predictive coefficient code obtained from an input audio signal and on a frequency-domain period. The variable-length coding part encodes a frequency-domain sequence derived from the input audio signal. A decoder of the present invention comprises a periodic-combined-envelope generating part and a variable-length decoding part. The periodic-combined-envelope generating part generates a periodic combined envelope sequence which is a frequency-domain sequence based on a spectral envelope sequence which is a frequency-domain sequence corresponding to a linear predictive coefficient code and on a frequency-domain period. The variable-length decoding part decodes a variable-length code to obtain a frequency-domain sequence.