Inter-Channel Phase Calculator for Stable Stereo Audio Encoding

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing audio coding technologies face challenges in stabilizing inter-channel phase differences for efficient coding, particularly for binauralized signals, leading to audible spatial fluctuations and energy loss due to phase shifts, especially when using smaller frequency bands for estimation.

Innovation Solution

An encoder system that calculates global and bandwise inter-channel phase differences, incorporating a stabilization mechanism by analyzing phase changes across time segments, using a closed interval and mean bandwise changes to minimize fluctuations, ensuring stable phase alignment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If inter-channel phase differences are estimated in smaller frequency bands, then phase stability over time is improved, but the number of transmitted phase differences increases, consuming more bits

Engineering Contradiction:

Improvephase stabilityVSAvoidnumber of transmitted phase differences

Core Design Contradiction:

Stability of the object's compositionVSQuantity of substance

Solution Approach 1:

The frequency band is divided into multiple smaller subbands, each with its own inter-channel phase difference estimator. This segmentation allows for more stable phase difference estimation in each subband while maintaining the ability to represent the full frequency spectrum. The patent applies this by creating multiple parallel processing paths for different frequency ranges.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Multiple subband phase difference estimates are combined through a stabilization mechanism that uses a low-pass filter to smooth the overall phase difference signal. This merging process reduces the number of effectively transmitted parameters by filtering out high-frequency variations, thereby reducing bit requirements while maintaining stability.

Inventive Principle:

Principle #5Merging (Combining)

2Measurement precision

If a larger number of inter-channel phase differences for smaller bands are transmitted, then phase estimation accuracy is improved, but the number of available bits for other parameters decreases

Engineering Contradiction:

Improvephase estimation accuracyVSAvoidavailable bits

Core Design Contradiction:

Measurement precisionVSQuantity of substance

Solution Approach 1:

Instead of transmitting phase differences for all possible subbands, the patent uses a selective approach where only the most relevant subband phase differences are transmitted. The stabilization mechanism allows the system to infer phase differences in less critical bands from the transmitted data, reducing the total number of bits needed while maintaining adequate accuracy.

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The patent dynamically adjusts the number and selection of transmitted phase difference parameters based on the audio signal characteristics. When the signal has stable phase characteristics, fewer parameters are transmitted; when variability is detected, more parameters are activated, optimizing the balance between accuracy and bit consumption.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If inter-channel phase differences are compensated to align channels, then downmix quality is improved, but spatial fluctuations occur when phase differences fluctuate over time

Engineering Contradiction:

Improvedownmix qualityVSAvoidspatial stability

Core Design Contradiction:

Manufacturing precisionVSStability of the object's composition

Solution Approach 1:

The patent implements a feedback mechanism where the estimated phase differences are continuously monitored and fed back into the stabilization process. The low-pass filter processes these feedback signals to smooth out fluctuations, creating a stable compensated phase difference that maintains both downmix quality and spatial consistency over time.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The stabilization mechanism acts as a protective buffer before phase compensation is applied. By pre-smoothing the phase difference estimates through the low-pass filter, the system cushions against the harmful effects of phase fluctuations, preventing them from propagating to the final downmix and causing spatial instability.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentUS20250299681A1Encoder comprising an inter-channel phase difference calculator device and method for operating such encoder

Publication Date: 2025.09.25 FRAUNHOFER GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG EV

AI summary

The invention provides an encoder for producing an audio bitstream from a stereo audio signal. The encoder comprises:a downmixer configured for downmixing the stereo audio signal in order to produce a mono audio signal;an inter-channel phase difference calculator device configured for calculating an inter-channel phase difference for each time segment of a plurality of consecutive time segments of the stereo audio signal; anda bitstream producer configured to produce the audio bitstream in such way that the mono audio signal and the inter-channel phase differences for the plurality of consecutive time segments are embedded in the audio bitstream;wherein the inter-channel phase difference calculator device comprises an inter-channel phase difference calculator being configured for calculating the inter-channel phase difference depending on a global inter-channel phase difference of a current time segment and depending on a mean bandwise inter-channel phase difference change of the current time segment.