Periodic Combined Envelope Coding for Pitch Peak Accuracy
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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 coding efficiency, especially at low bit-rates.
Innovation Solution
An encoder and decoder system that generates and uses a periodic combined envelope sequence, which is a frequency-domain sequence based on spectral envelope sequences and period codes, to enhance coding accuracy around pitch period peaks with a minimal code amount.
Engineering Contradictions & Design Principles
Engineering 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
Solution Approach 1:
The patent combines the spectral envelope obtained from linear predictive coefficients with a periodic envelope generated from pitch period information. This merging allows the system to maintain the code efficiency of linear predictive coding while adding pitch-related accuracy through the periodic envelope component, thereby resolving the contradiction between code amount and approximation accuracy around pitch peaks.
Solution Approach 2:
The patent creates a composite envelope structure by combining two different envelope representations: the spectral envelope from linear predictive analysis and the periodic envelope from pitch period detection. This composite approach integrates the strengths of both methods, achieving both compact coding and high accuracy around pitch period peaks simultaneously.
2Productivity
If variable length coding is used on normalized coefficient strings, then coding efficiency improves, but accuracy around pitch period peaks deteriorates
Solution Approach 1:
Before performing variable length coding on the normalized coefficient strings, the patent merges the spectral envelope with a periodic envelope derived from pitch period information. This pre-processing step ensures that pitch-related characteristics are preserved in the envelope, allowing variable length coding to maintain both efficiency and accuracy around pitch period peaks.
Data Source
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.