Audio Encoder Spectral Envelope Coding for Pitch Peak Accuracy
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Solution Overview
Problem
Existing audio signal coding methods face low coding efficiency due to low approximation accuracy of spectral envelopes around peaks caused by the pitch period, especially when using linear predictive coefficients, which require a large amount of code for transmission.
Innovation Solution
The development of an encoder and decoder that utilize a periodic combined envelope sequence, generated by combining amplitude spectral envelopes with periodic envelopes, to achieve high approximation accuracy around pitch period peaks using a small amount of code.
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 two types of spectral envelopes: a first spectral envelope obtained from linear predictive coefficients (providing low code amount) and a second spectral envelope obtained from the frequency domain representation of the input signal (providing high approximation accuracy around pitch period peaks). By merging these two envelopes, the invention achieves both low code amount and high approximation accuracy, resolving the technical contradiction between code amount and measurement precision.
2Loss of information
If spectral envelope code is transmitted to decoding side, then spectral envelope information is obtained, but code amount increases
Solution Approach 1:
The patent extracts only the essential spectral envelope information needed for high approximation accuracy around pitch period peaks by using a second spectral envelope derived from the frequency domain representation of the input signal. This extraction approach transmits minimal code while maintaining the necessary spectral envelope information, resolving the contradiction between information completeness and code amount.
3Productivity
If variable length coding is used for normalized coefficient strings, then coding efficiency is improved, but approximation accuracy around pitch period peaks must be sufficient
Solution Approach 1:
The patent changes the parameter used for spectral envelope representation by introducing a second spectral envelope derived from the frequency domain representation of the input signal, specifically tailored to improve approximation accuracy around pitch period peaks. This parameter change enables better precision while maintaining coding efficiency through variable length coding of the normalized coefficient strings.
Data Source
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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.