Audio Spectrum Flatness Control via Energy Envelope Smoothing
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Solution Overview
Problem
Current audio/speech digital signal communication systems face challenges in maintaining high frequency band quality due to low bit rate encoding, leading to distorted signals when bandwidth extension techniques like SBR are used, as they often result in a non-flat energy envelope in the high frequency band.
Innovation Solution
A method and system for decoding audio bitstreams that involves generating high band coefficients by copying low band coefficients to high frequency locations, modifying the energy envelope to flatten or smooth these coefficients, and applying a spectral envelope to improve spectrum flatness, all without requiring additional bits, thereby enhancing the quality of the decoded audio signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If bandwidth extension techniques like SBR are used to reduce bit rate, then transmission bandwidth is reduced, but the high frequency band quality deteriorates due to non-flat energy envelope
Solution Approach 1:
The patent modifies the energy envelope parameters of the high frequency band by applying smoothing filters and adjusting spectral characteristics. This changes the parameter distribution to achieve a flatter energy envelope, thereby improving high frequency quality without increasing bit rate
Solution Approach 2:
The patent copies spectral characteristics from the low frequency band to the high frequency band. By replicating and adapting the spectral envelope patterns, the system reconstructs realistic high frequency content that maintains natural sound quality while using minimal transmission resources
2Productivity
If low bit rate encoding is used to reduce transmission bandwidth, then transmission efficiency is improved, but signal distortion increases in the high frequency band
Solution Approach 1:
The patent introduces an energy envelope smoothing mechanism as an intermediary between the encoded low frequency data and the reconstructed high frequency signal. This intermediary process generates appropriate spectral characteristics that prevent distortion while maintaining low bit rate transmission
Solution Approach 2:
The patent applies energy envelope smoothing and spectral shaping in advance during the decoding process, before the final signal reconstruction. This preliminary processing ensures that the high frequency band is pre-configured with appropriate spectral characteristics, preventing distortion from occurring in the first place
Data Source
AI summary
In accordance with an embodiment, a method of decoding an encoded audio bitstream at a decoder includes receiving the audio bitstream, decoding a low band bitstream of the audio bitstream to get low band coefficients in a frequency domain, and copying a plurality of the low band coefficients to a high frequency band location to generate high band coefficients. The method further includes processing the high band coefficients to form processed high band coefficients. Processing includes modifying an energy envelope of the high band coefficients by multiplying modification gains to flatten or smooth the high band coefficients, and applying a received spectral envelope decoded from the received audio bitstream to the high band coefficients. The low band coefficients and the processed high band coefficients are then inverse-transformed to the time domain to obtain a time domain output signal.