Multichannel Audio Encoder With Adaptive Spectral Shaping
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Solution Overview
Problem
Existing audio encoders face challenges in efficiently encoding multi-channel audio signals when signals are highly correlated, as they often use different spectral envelopes, leading to issues such as unmasking and increased noise, especially when different channels are processed separately, resulting in suboptimal perceptual quality and artifacts.
Innovation Solution
An audio encoder that adaptively adjusts spectral shaping by using channel-specific or joint parameters based on signal characteristics, such as harmonicity measures, to optimize noise shaping and stereo processing, thereby improving perceptual quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If different spectral envelopes are used for different channels, then channel-specific signal characteristics can be optimized, but unmasking artifacts and increased noise occur in correlated signals
Solution Approach 1:
The patent applies dynamics by making the spectral envelope selection adaptive rather than fixed. The system dynamically switches between channel-specific spectral envelopes and a shared spectral envelope based on the correlation characteristics of the audio signal. When channels are highly correlated, the shared spectral envelope is used to avoid unmasking artifacts. When channels are less correlated, channel-specific spectral envelopes are applied to optimize signal representation. This dynamic adaptation resolves the contradiction between optimization and artifact generation.
Solution Approach 2:
The patent changes the parameter of spectral envelope selection based on signal characteristics. By monitoring channel correlation and adjusting the spectral envelope parameters accordingly, the system transitions between different encoding modes. This parameter change allows the system to maintain high spectral envelope optimization when needed while avoiding harmful artifacts in correlated signal conditions.
2Measurement precision
If channels are processed separately with different spectral tilts, then individual channel quality improves, but energy compaction in stereo processing decreases
Solution Approach 1:
The system dynamically adjusts spectral tilt parameters based on channel correlation characteristics. When channels are highly correlated, the system uses a shared spectral tilt to preserve energy compaction properties necessary for effective stereo processing. When channels are less correlated, individual channel spectral tilts are applied to optimize individual channel quality. This dynamic parameter adjustment resolves the contradiction between individual quality and energy compaction.
3Loss of energy
If a single spectral tilt is used for all channels, then stereo processing energy compaction is maintained, but channel-specific signal characteristics are not optimized
Solution Approach 1:
The patent implements a dynamic spectral tilt selection mechanism that adapts to signal conditions. Rather than using a fixed single spectral tilt, the system monitors channel correlation and dynamically switches between shared and channel-specific spectral tilts. This allows the system to maintain energy compaction when correlated signals require it, while enabling channel-specific optimization when signal characteristics warrant it.
Solution Approach 2:
The system changes the spectral tilt parameter from a fixed value to an adaptive parameter that varies based on channel correlation characteristics. This parameter change enables the system to optimize for either energy compaction or channel-specific characteristics depending on the signal conditions, resolving the contradiction between these two opposing requirements.
4Measurement precision
If channel-specific parameters are used for spectral shaping, then perceptual quality for uncorrelated signals improves, but processing complexity increases
Solution Approach 1:
The patent applies local quality by tailoring the spectral shaping parameters to the specific characteristics of each channel or signal group. Instead of applying a uniform processing approach, the system identifies whether channels are correlated or uncorrelated and applies appropriate spectral tilts accordingly. This localized adaptation improves perceptual quality for uncorrelated signals while avoiding the unnecessary complexity of processing correlated signals with different spectral tilts.
Data Source
AI summary
An audio encoder for a multichannel audio signal includes: a signal shaping unit to shape each channel using a number of scale parameters, configured to derive, for each channel, a number of scale parameters; a stereo processing unit to receive the shaped channels and provide a joint shaped audio signal from the shaped channels, a coded signal writer, to form a coded signal with at least the joint shaped audio signal; and a characteristic determiner to determine a characteristic from the channels having a characteristic state selected between a first characteristic state and a second characteristic state. The signal shaping unit is controlled by the characteristic determiner to derive: in the first characteristic state, the number of scale parameters using a channel-specific parameter for the channel; and in the second characteristic state, the number of scale parameters using a joint parameter derived from the first channel and the second channel.