Gain Factor Attenuation for Wideband Speech Coding
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Solution Overview
Problem
Existing wideband speech coding technologies face challenges in efficiently extending narrowband speech coders to support wideband frequency ranges without significant bandwidth increase or computational complexity, particularly in mobile and embedded applications, and often require transcoding, which is impractical.
Innovation Solution
A method that calculates and attenuates gain factor values based on the time-varying relation between low-frequency and high-frequency envelopes of a speech signal, allowing for efficient wideband speech coding with minimal bandwidth increase and avoiding transcoding, by using a system with envelope calculators and gain factor attenuators to process narrowband and highband signals separately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If wideband speech coding is implemented using narrowband coding techniques scaled to cover wideband spectrum, then wideband frequency range support is achieved, but computational complexity increases significantly and bandwidth increases unacceptably
Solution Approach 1:
The speech signal is divided into narrowband portion (0-4 kHz) and highband portion (4-8 kHz). The narrowband portion is encoded using conventional narrowband coding techniques, while the highband portion is generated by extrapolating the spectral envelope from the narrowband spectral envelope. This segmentation allows wideband speech coding without requiring computationally intensive wideband CELP coding throughout the entire frequency range.
Solution Approach 2:
A spectral envelope extrapolation mechanism serves as an intermediary to generate the highband spectral envelope from the narrowband spectral envelope. This intermediary approach allows the highband signal to be derived without direct measurement or intensive processing of the highband signal itself, reducing computational complexity while maintaining speech quality.
2Adaptability or versatility
If wideband speech coding is implemented using narrowband coding techniques scaled to cover wideband spectrum, then wideband frequency range support is achieved, but bandwidth increases unacceptably
Solution Approach 1:
The highband signal is extracted and generated through spectral envelope extrapolation rather than being directly transmitted. By deriving the highband portion from the narrowband spectral envelope through mathematical extrapolation, the system avoids transmitting redundant highband information, thus minimizing bandwidth increase to only about 800-1000 bps.
3Quantity of substance
If spectral envelope extrapolation is used to extend highband from narrowband spectral envelope, then bandwidth increase is minimized and transcoding is avoided, but spectral envelope accuracy deteriorates
Solution Approach 1:
The gain factor is made dynamic and time-varying rather than fixed. The gain factor values are calculated based on the time-varying relation between the narrowband signal envelope and highband signal envelope, allowing the system to adapt to changing speech conditions. This dynamic adjustment compensates for inaccuracies in spectral envelope extrapolation by optimizing the scaling of the extrapolated highband signal in real-time.
Data Source
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AI summary
A method of signal processing according to one embodiment includes calculating an envelope of a first signal that is based on a low-frequency portion of a speech signal, calculating an envelope of a second signal that is based on a high-frequency portion of the speech signal, and calculating a plurality of gain factor values according to a time-varying relation between the envelopes of the first and second signal. The method includes attenuating, based on a variation over time of a relation between the envelopes of the first and second signals, at least one of the plurality of gain factor values. In one example, the variation over time of a relation between the envelopes is indicated by at least one distance among the plurality of gain factor values.