HOA Signal Direction Encoding for Low-Bit-Rate Compression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Higher Order Ambisonics (HOA) representations require high bit rates for transmission, making them unsuitable for low-bit-rate applications like audio streaming to mobile devices, as existing compression methods typically result in data rates higher than 256 kbit/s, which is excessive for such applications.
Innovation Solution
A method for low-bit-rate compression of HOA representations by decomposing the signal into frequency sub-bands, approximating coefficients using a truncated HOA representation and predicted directional sub-band signals, and encoding direction information efficiently using partial de-correlation and parametric representation, reducing the need for extra side information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If HOA representation is transmitted with high quality (order N=4, sampling rate 48 kHz, 16 bits per sample), then sound field representation quality is improved, but bit rate increases to 19.2 MBits/s which is too high for practical applications
Solution Approach 1:
The HOA representation is decomposed into multiple frequency sub-bands using a filter bank. Each sub-band is processed independently with direction-of-arrival estimation and parametric coding, allowing selective transmission of important directional information while compressing ambient components, thereby achieving low bit-rate transmission without sacrificing overall sound field quality
Solution Approach 2:
The patent transforms the HOA coefficient representation into a parametric model that includes direction-of-arrival parameters, spectral envelopes, and residual components. By encoding only the essential parameters rather than full HOA coefficients, the bit rate is dramatically reduced from 19.2 MBits/s to practical levels while preserving perceptual quality
2Quantity of substance
If existing compression methods are used to reduce HOA data rate, then bit rate is reduced, but data rate remains above 256 kbit/s which is still too high for mobile streaming applications
Solution Approach 1:
The patent extracts and separately encodes directional signals from the HOA representation using direction-of-arrival estimation in each sub-band. By isolating and efficiently coding only the directional components with parametric models, the remaining ambient information can be heavily compressed, achieving bit rates suitable for mobile streaming
Solution Approach 2:
Instead of fully encoding all HOA coefficients, the patent applies partial encoding by selecting only the most significant directional parameters and spectral features for transmission. This selective approach achieves sufficient perceptual quality at bit rates appropriate for mobile devices
Data Source
AI summary
Encoding of Higher Order Ambisonics (HOA) signals commonly results in high data rates. For data rate reduction, a method (100) for encoding direction information for frames of an input HOA signal comprises determining (s101) active candidate directions (I) among predefined global directions having global direction indices, dividing (s102) the input HOA signal into frequency subbands (II), determining (s103) for each frequency subband active subband directions among the active candidate directions, assigning (s104) a relative direction index to each direction per subband, assembling (s105) direction information for the frame, the direction information comprising the active candidate directions (I), for each subband and each active candidate direction a bit indicating whether or not the active candidate direction is an active subband direction for the respective frequency subband, and for each frequency subband the relative direction indices of active subband directions in the second set of subband directions, and transmitting (s106) the assembled direction information.