HOA Gain Value Bit Allocation for Random-Access Audio Compression
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Solution Overview
Problem
Existing HOA compression methods do not efficiently determine the minimum number of bits required for representing non-differential gain values, which are crucial for reconstructing the original signal amplitudes without temporal jumps and facilitating random access, due to the lack of constraints on the value ranges of HOA representations.
Innovation Solution
An apparatus that establishes an inter-relation between the value range of input HOA representations and potential maximum gains, determining the minimum number of bits required for encoding non-differential gain values by using a processing method that normalizes the HOA data frames to ensure compliance with specified value range constraints, and applies a mixing matrix to ensure efficient coding of exponents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If HOA representations are compressed using conventional methods without value range constraints, then flexibility in representation is maintained, but the number of bits required for representing gain values increases and compression efficiency deteriorates
Solution Approach 1:
The patent applies parameter changes by establishing specific value range constraints on HOA representation parameters (channel signals normalized to [-1, 1[ range) and deriving corresponding constraints on gain values. This allows determining the minimum number of bits required for gain value representation, optimizing compression efficiency while maintaining representation flexibility.
2Productivity
If the number of bits for representing gain values is reduced, then compression efficiency improves, but the ability to accurately represent amplitude changes deteriorates
Solution Approach 1:
The patent replaces arbitrary or excessive bit allocation with a mathematically derived minimum bit requirement based on the normalized value ranges. By substituting the mechanical approach of fixed bit allocation with a calculated approach based on signal bounds, the system achieves optimal precision without waste.
3Reliability
If gain control processing is applied to attenuate or amplify signals before perceptual encoding, then signal amplitude requirements are satisfied, but additional side information and complexity are introduced
Solution Approach 1:
The patent applies preliminary action by normalizing HOA channel signals to the [-1, 1[ range before gain control processing and perceptual encoding. This pre-normalization ensures that subsequent gain operations remain within predictable bounds, reducing the complexity of gain value representation and eliminating the need for extensive side information.
Data Source
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AI summary
When compressing an HOA data frame representation, a gain control (15, 151) is applied for each channel signal before it is perceptually encoded (16). The gain values are transferred in a differential manner as side information. However, for starting decoding of such streamed compressed HOA data frame representation absolute gain values are required, which should be coded with a minimum number of bits. For determining such lowest integer number (βe) of bits the HOA data frame representation (C(k)) is rendered in spatial domain to virtual loudspeaker signals lying on a unit sphere, followed by normalisation of the HOA data frame representation (C(k)). Then the lowest integer number of bits is set to βe=log2log2KMAX⋅O+1.