Periodic Envelope Audio Coding for Accurate Pitch Peak Reconstruction
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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 a periodic combined envelope sequence based on spectral envelope sequences and period codes, allowing for high approximation accuracy around pitch period peaks using a small code amount, by incorporating a periodic-combined-envelope generating part and variable-length coding/decoding parts.
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 spectral envelope is segmented into two parts: a base spectral envelope obtained from linear predictive coefficients, and a periodic component representing pitch period peaks. This segmentation allows independent optimization of each part, maintaining low code amount for the base while accurately representing pitch peaks through the periodic component.
Solution Approach 2:
The patent combines the base spectral envelope (from linear predictive coefficients) with a periodic component (representing pitch period peaks) to create a composite spectral envelope. This merging integrates the advantages of both approaches: low code amount from LPC and high accuracy at pitch peaks from the periodic component.
2Measurement precision
If more code is used to represent spectral envelope, then approximation accuracy around pitch period peaks is improved, but coding efficiency deteriorates
Solution Approach 1:
Instead of representing the entire spectral envelope with high precision, the patent applies partial action by focusing computational resources only on the pitch period peaks. The periodic component adds precision only where needed (at pitch peaks) while keeping the overall code amount low, thus maintaining coding efficiency.
3Quantity of substance
If variable-length coding is performed on normalized coefficient strings, then code amount is reduced, but decoding accuracy deteriorates without accurate spectral envelope
Solution Approach 1:
The spectral envelope (including the periodic component) is calculated and made available before variable-length coding of the normalized coefficient strings. This preliminary action ensures that the decoder has accurate spectral envelope information to properly reconstruct the audio signal, maintaining decoding accuracy while still using compact variable-length coding.
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.