Dead-Zone Audio Quantization Guided by Spectral Tonality
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Solution Overview
Problem
In very-low-bit-rate audio coding, musical noise artifacts occur due to insufficient bit allocation, particularly in stationary music or noise spectra, where transform lines are quantized to zero or not, leading to a tonal character in the decoded signal and inefficient bit usage, especially at low frequencies where the human auditory system is sensitive.
Innovation Solution
An audio encoder with a signal-adaptive dead-zone quantization scheme that modifies the dead-zone based on tonality indicating values for spectral lines or groups, allowing per-bin or per-band dead-zone selection before quantization, reducing complexity and side-information requirements, and optimizing audio quality by varying the dead-zone size based on frequency and tonality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed dead-zone quantization is used, then the encoding complexity is low, but musical noise artifacts occur and audio quality deteriorates
Solution Approach 1:
The patent applies dynamics by making the dead-zone size adaptive rather than fixed. The quantizer modifies its dead-zone parameter based on the instantaneous tonality of the spectral lines, allowing the system to adapt to different signal characteristics in real-time, thereby reducing musical noise while maintaining manageable complexity through localized adaptation decisions
Solution Approach 2:
The patent changes the dead-zone parameter dynamically based on tonality indication. By calculating a tonality value for each spectral line and adjusting the dead-zone size accordingly (larger dead-zone for non-tonal lines, smaller or zero for tonal lines), the system optimizes quantization performance adaptively without requiring complete system redesign
2Object-affected harmful factors
If the dead-zone is adapted on the entire spectrum, then musical noise is reduced, but the device complexity and bit-rate increase
Solution Approach 1:
The patent applies local quality by treating different spectral lines individually based on their tonality characteristics rather than applying a uniform adaptation across the entire spectrum. Each spectral line receives a customized dead-zone size according to its local tonality property, optimizing quality where needed while avoiding unnecessary complexity in regions where simple quantization suffices
Solution Approach 2:
The patent segments the spectrum into individual spectral lines or small groups, evaluating tonality and applying dead-zone adaptation independently to each segment. This segmentation allows the system to manage complexity by processing small units separately rather than adapting the entire spectrum as a single complex operation
3Object-affected harmful factors
If optimal dead-zone quantization is used, then audio quality improves, but 2 bits of side-information must be transmitted increasing bit-rate
Solution Approach 1:
The patent applies self-service by deriving the tonality indication and dead-zone selection information directly from the spectral content itself, without requiring external side-information transmission. The tonality calculation uses the spectral magnitudes already present in the encoded signal, allowing the quantizer to adapt optimally using only the signal's own characteristics
4Object-affected harmful factors
If bits are allocated to tonal spectral regions, then tonal quality is maintained, but bits are wasted in regions where the human auditory system is less sensitive
Solution Approach 1:
The patent changes the quantization parameter (dead-zone size) based on tonality detection, applying smaller or zero dead-zones to tonal spectral lines to preserve their quality, while applying larger dead-zones to non-tonal lines where the human auditory system is less sensitive. This parameter adaptation optimizes bit allocation efficiency by concentrating bits where they provide the most perceptual benefit
Data Source
AI summary
The invention provides an audio encoder for encoding an audio signal so as to produce therefrom an encoded signal, the audio encoder including: a framing device configured to extract frames from the audio signal; a quantizer configured to map spectral lines of a spectrum signal derived from the frame of the audio signal to quantization indices, wherein the quantizer has a dead-zone, in which the input spectral lines are mapped to quantization index zero; and a control device configured to modify the dead-zone; wherein the control device includes a tonality calculating device configured to calculate at least one tonality indicating value for at least one spectrum line or for at least one group of spectral lines, wherein the control device is configured to modify the dead-zone for the at least one spectrum line or the at least one group of spectrum lines depending on the respective tonality indicating value.