Audio Upmix Parameter Interpolation to Reduce Audible Modulation
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Solution Overview
Problem
Conventional binaural cue coding decoders produce degraded multi-channel audio output when side information is received at a lower update frequency than the downmix audio signal, leading to poor audio quality due to unnecessary amplitude modulation.
Innovation Solution
An apparatus and method for upmixing a downmix audio signal using temporally variable upmixing parameters, where the parameter interpolator separately interpolates the magnitude and phase values of complex-valued upmix parameters to minimize amplitude variation, ensuring smooth transitions and reducing audible modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional interpolation approaches are used to derive intermediate parameters at the decoder side, then the decoder can apply parameters continuously over time, but the audio quality deteriorates due to poor interpolation results causing unnecessary amplitude modulation
Solution Approach 1:
The patent segments the complex-valued upmix parameter into two independent components: magnitude value and phase value. This segmentation allows separate interpolation processing for each component, preventing the interaction that causes amplitude modulation artifacts in conventional approaches.
Solution Approach 2:
The patent changes the interpolation approach by applying linear interpolation separately to magnitude and phase parameters rather than interpolating the complex parameter directly. This parameter transformation resolves the technical contradiction by maintaining continuous parameter application while eliminating harmful amplitude modulation effects.
2Loss of energy
If the update frequency of side information is reduced to save transmission bandwidth, then transmission efficiency improves, but audio quality deteriorates due to insufficient parameter updates
Solution Approach 1:
The patent performs preliminary separation of magnitude and phase values from the complex upmix parameters before transmission. This preliminary action enables the decoder to reconstruct high-quality parameters through separate interpolation, maintaining audio quality even when side information is transmitted at lower update frequencies.
Solution Approach 2:
By transforming the complex parameter representation into separate magnitude and phase components, the system enables efficient low-frequency transmission while maintaining high-quality reconstruction through independent interpolation of each parameter type.
3Device complexity
If complex-valued upmix parameters are interpolated directly without separating magnitude and phase, then interpolation is simpler to implement, but audible modulation artifacts are introduced
Solution Approach 1:
The patent applies segmentation by dividing the complex parameter interpolation task into two separate real-valued interpolation operations: one for magnitude and one for phase. This segmentation eliminates the harmful interactions that occur in direct complex interpolation while keeping the implementation straightforward.
Solution Approach 2:
The patent transforms the interpolation operation from complex domain to separate real-valued domains (magnitude and phase), achieving both simplicity and audio quality by avoiding the mathematical operations that cause modulation artifacts in direct complex interpolation.
Data Source
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AI summary
An apparatus for upmixing a downmix audio signal describing one or more downmix audio channels into an upmixed audio signal describing a plurality of upmixed audio channels comprises an upmixer configured to apply temporally variable upmixing parameters to upmix the downmix audio signal in order to obtain the upmixed audio signal. The apparatus also comprises a parameter interpolator, wherein the parameter interpolator is configured to obtain one or more temporally interpolated upmix parameters to be used by the upmixer on the basis of a first complex-valued upmix parameter and a subsequent second complex-valued upmix parameter. The parameter interpolator is configured to separately interpolate between a magnitude value of the first complex-valued upmix parameter and a magnitude value of the second complex-valued upmix parameter, and between a phase value of the first complex-valued upmix parameter and a phase value of the second complex-valued upmix parameter, to obtain the one or more temporally interpolated upmix parameters. A respective method can be implemented, for example, as a computer program.