LFE Frame Loss Concealment Using LPC Bandwidth Sharpening
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Solution Overview
Problem
Existing frame loss concealment techniques for low-frequency effects (LFE) channels in multi-channel audio, such as those used in 5.1 or 7.1 audio, result in annoying low-frequency rumble due to their inefficiency in handling very low frequency content, especially when applied over error-prone wireless transmissions.
Innovation Solution
A method utilizing linear predictive coding (LPC) with bandwidth sharpening to generate substitution frames by modifying LPC synthesis filters, ensuring stability and extending impulse responses to handle frame losses in LFE channels, and optionally applying a subband approach for complex signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional frame loss concealment techniques are applied to LFE channels, then the techniques can be reused with existing systems, but they produce annoying low-frequency rumble due to inefficiency in handling very low frequency content
Solution Approach 1:
The patent modifies the LPC synthesis filter by changing its parameters - specifically extending the impulse response duration and adjusting the filter coefficients to better suit very low frequency content. This parameter modification allows the filter to generate more accurate substitution frames for LFE channels without producing rumble artifacts.
Solution Approach 2:
The patent separates the handling of different frequency channels by applying specialized processing only to the LFE channel when frame loss is detected. The system identifies which channel experienced frame loss and applies the modified LPC technique selectively, rather than uniformly to all channels, thus optimizing performance for low-frequency content while maintaining efficiency.
2Device complexity
If MDCT coefficients are reused with gain scaling and sign prediction for LFE frame loss concealment, then the process is simple, but it results in poor quality reconstruction with rumble artifacts
Solution Approach 1:
The patent replaces the simple gain scaling and sign prediction mechanism with a more sophisticated LPC-based synthesis filter approach. This substitution introduces a resonator that is tuned to the low-frequency characteristics of the LFE channel, providing much better reconstruction quality by modeling the physical characteristics of low-frequency sound propagation.
Solution Approach 2:
The patent performs preliminary tuning of the resonator parameters based on the available valid frame data before generating the substitution frame. By pre-adjusting the filter coefficients to match the spectral characteristics of the LFE channel, the system ensures high-quality reconstruction without requiring complex real-time adjustments during the concealment process.
3Manufacturing precision
If the impulse response of the audio filter is extended through bandwidth sharpening, then the filter better handles low-frequency content, but the filter may become unstable
Solution Approach 1:
The patent dynamically adjusts the bandwidth sharpening factor based on the specific characteristics of each lost frame and the surrounding valid frames. Rather than applying a fixed extension to the impulse response, the system adaptively modifies the filter parameters to achieve the necessary low-frequency accuracy while maintaining stability constraints, allowing optimal performance under varying conditions.
Data Source
AI summary
A method of generating a substitution frame for a lost audio frame of an audio signal is presented. The method may comprise determining an audio filter based on samples of a valid audio frame preceding the lost audio frame. The method may comprise generating the substitution frame based on the audio filter and the samples of the valid audio frame preceding the lost audio frame. The method may be advantageously applied to a low frequency effects (LFE) channel of a multi-channel audio signal.