Downward-Compatible Audio Downmix With Dynamic Spectral Correction
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Solution Overview
Problem
Current automatic downmix methods for sound formats, such as those using ITU-R BS.775 and Logic 7, fail to adequately compensate for phantom sound source shifts, level differences, and tone changes when converting multi-channel audio to two-channel formats, leading to suboptimal playback quality.
Innovation Solution
The proposed method dynamically corrects spectral values of overlapping time windows to form sum signals, using analysis and correction blocks that apply transformations and adjustments based on energy content comparisons in specific frequency bands, ensuring balanced levels and minimizing tone changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If automatic downmix methods (ITU-R BS.775, Logic 7) are used to convert multi-channel audio to two-channel formats, then channel compatibility is achieved, but phantom sound source shifts and tone changes occur
Solution Approach 1:
The patent applies dynamics by making the downmix process adaptive rather than static. The method dynamically adjusts the downmix coefficients based on the analyzed energy distribution across frequency bands and channels. This allows the system to maintain accurate phantom sound source positioning by responding to the actual signal characteristics in real-time, rather than applying fixed transformation matrices that cause position shifts.
Solution Approach 2:
The patent implements feedback by analyzing the energy content of the multi-channel signal and using this information to correct the downmix process. The system measures the energy distribution in different frequency bands and channels, then feeds this information back to adjust the mixing coefficients accordingly. This feedback mechanism compensates for phantom sound source shifts and maintains accurate spatial positioning in the downmixed two-channel output.
2Adaptability or versatility
If automatic downmix methods are used to convert multi-channel audio to two-channel formats, then playback compatibility is achieved, but level differences and tone changes occur
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the energy levels and frequency characteristics during the downmix process. Instead of applying uniform level adjustments, the system analyzes the energy content in different frequency bands and channels, then modifies the mixing parameters to compensate for level differences and tone changes. This ensures that the downmixed signal maintains accurate level relationships and frequency balance.
Solution Approach 2:
The patent makes the downmix process dynamic by continuously analyzing the signal characteristics and adjusting the mixing parameters accordingly. The system adapts the downmix coefficients based on the actual energy distribution in the multi-channel signal, rather than applying static transformation matrices. This dynamic approach preserves level accuracy and tone quality across different playback conditions.
3Adaptability or versatility
If simulcast of all sound formats is generated during audio production, then playback device compatibility is ensured, but production effort increases considerably
Solution Approach 1:
The patent applies preliminary action by performing the downmix operation just-in-time during playback rather than requiring all formats to be pre-generated during production. The system prepares the necessary processing algorithms and energy analysis frameworks in advance, but actually performs the channel conversion when needed. This eliminates the need for multiple pre-mixed versions while ensuring compatibility.
Solution Approach 2:
The patent extracts the channel conversion function from the production process and moves it to the playback process. Instead of requiring all downmix operations to be performed during audio production, the system extracts and applies the necessary transformation algorithms at playback time. This separation reduces production complexity while maintaining playback compatibility.
Data Source
AI summary
A method of generating an audio output signal according to a downward compatible sound format, the method including: generating a sum signal by combining a first input channel signal with a second input channel signal; and dynamically correcting the sum signal using samples of the first and second input channel signals from overlapping time windows.