Audio Encoder Using Periodic Combined Envelopes for Pitch Peaks

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Solution Overview

Problem

Existing audio signal coding methods, such as those using linear predictive coefficients, suffer from low approximation accuracy around peaks caused by the pitch period of audio signals, leading to inefficient variable-length coding.

Innovation Solution

An encoder and decoder that generate and use a periodic combined envelope sequence, which enhances frequency-domain representation by incorporating both spectral envelope and periodicity information, allowing for high approximation accuracy with a small code amount.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If linear predictive coefficients are used to represent 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 spectral envelope representation is segmented into two parts: linear predictive coefficients for general spectral shape and periodicity information for pitch-related peaks. This segmentation allows each component to specialize in representing different aspects, improving overall accuracy without proportionally increasing code amount.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention merges linear predictive coefficients with periodicity information to create a hybrid representation. By combining these two types of information, the system achieves both compact coding (from LPC) and accurate pitch peak representation (from periodicity info).

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 3:

Different representation methods are applied to different regions of the spectrum: linear predictive coefficients handle the overall spectral envelope while periodicity information specifically enhances the representation of pitch-related peaks. This local specialization improves accuracy where needed without uniformly increasing complexity.

Inventive Principle:

Principle #3Local quality

2Productivity

If spectral envelope is accurately represented around pitch peaks, then coding efficiency improves, but code amount increases

Engineering Contradiction:

Improvecoding efficiencyVSAvoidcode amount

Core Design Contradiction:

ProductivityVSQuantity of substance

Solution Approach 1:

Instead of fully representing the spectral envelope with high precision across all frequencies, the invention applies enhanced representation (periodicity information) only partially - specifically targeted at pitch-related regions. This partial action improves coding efficiency in critical areas without proportionally increasing overall code amount.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The invention changes the representation parameters by introducing periodicity information alongside linear predictive coefficients. This parameter change allows the system to achieve better approximation accuracy in pitch regions while maintaining a relatively compact code structure through efficient encoding of the additional parameters.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS10607616B2Encoder, decoder, coding method, decoding method, coding program, decoding program and recording medium

Publication Date: 2020.03.31 NIPPON TELEGRAPH & TELEPHONE CORP

AI summary

An encoder and a decoder are provided that are capable of reproducing a frequency-domain envelope sequence that provides high approximation accuracy around peaks caused by the pitch period of an audio signal by using a small amount of code. 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.