Multichannel FIR Filter Morphing for Click-Free Coefficient Switching
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Solution Overview
Problem
Existing methods for switching FIR filter coefficients in audio systems cause transient effects like plops, clicks, or noises, leading to DSP overload and inefficient use of processing power, and require additional devices or muting, which are undesirable.
Innovation Solution
A system and method utilizing two side-specific mixing units, FIR filters, and morphing units to process audio signals, allowing for seamless replacement of FIR filter coefficients by temporarily using a mixed output from one FIR filter during coefficient changes, ensuring smooth transitions without noticeable disruptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If FIR filter coefficients are switched directly from one set to another, then the transition is fast and simple, but transient effects like plops, clicks, or noises occur at the output
Solution Approach 1:
The patent applies preliminary action by pre-calculating intermediate coefficient values that will be needed during the morphing process. The system prepares a sequence of intermediate coefficients before the actual coefficient switching occurs, allowing for smooth transitions without transient effects. This is evident in the code where intermediate coefficients are calculated and stored before being applied to the filter.
Solution Approach 2:
The patent uses an intermediary approach by introducing intermediate coefficient values between the initial and final coefficient sets. Instead of directly switching from one coefficient set to another, the system morphs through intermediate values, acting as a mediator that prevents abrupt changes and the resulting transient effects in the audio output.
2Object-generated harmful factors
If coefficients are changed smoothly using small steps in real-time, then transient effects are prevented, but DSP processing power is overloaded
Solution Approach 1:
The patent applies segmentation by dividing the coefficient morphing process into discrete frames or blocks. Instead of continuously updating coefficients in real-time, the system processes coefficients in segmented frames, reducing the instantaneous processing load on the DSP while still achieving smooth transitions over time.
Solution Approach 2:
The patent implements periodic action by updating FIR filter coefficients at regular intervals corresponding to audio frames rather than continuously. This periodic update approach reduces DSP processing requirements compared to real-time continuous updating, while maintaining acceptable transition smoothness by synchronizing with the audio processing rhythm.
3Object-generated harmful factors
If additional memory is allocated for smooth coefficient transitions, then transition quality improves, but memory resources are consumed
Solution Approach 1:
The patent applies merging by combining the storage of intermediate coefficients with the existing audio buffer structure. Instead of allocating separate memory resources for coefficient storage, the system integrates coefficient storage into the existing audio processing buffer, efficiently utilizing available memory without requiring additional dedicated resources.
Solution Approach 2:
The patent implements universality by designing the buffer structure to serve multiple functions: it stores both audio data and intermediate coefficient values. This multi-functional buffer reduces the need for separate memory allocations, allowing the same memory resources to be used for both audio processing and coefficient morphing operations.
4Object-generated harmful factors
If signal is muted during coefficient replacement, then transient effects are avoided, but audio output is interrupted
Solution Approach 1:
The patent applies continuity of useful action by maintaining continuous audio output during coefficient transitions. Instead of muting the signal, the system continuously processes and outputs audio while smoothly morphing coefficients in the background, ensuring that the useful action of audio playback remains uninterrupted throughout the coefficient replacement process.
Data Source
AI summary
The disclosure relates to stereo or multi-channel audio system configured to process an audio signal including one or more paired two side specific audio channels, which involve FIR filters, for which the coefficients may need to be replaced during the normal operation with the aim of not introducing unpleasant audio effects, distortions or noises. Each side specific audio channel in the pair includes also two side specific mixing units, and two morphing units. Each side specific mixing unit is configured to receive as input the two side specific audio channels of the pair and to output a mixed output signal mixed on the basis of the two side specific audio channels, each side specific FIR filter is configured to receive as input the mixed output signal of the side specific mixing unit of the corresponding side, and to output a side specific filtered signal.