Audio Signal Synthesis Using Adaptive Band-Pass Filters
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Solution Overview
Problem
Existing audio processing technologies face challenges in efficiently decomposing and re-synthesizing audio signals, particularly in music processing, due to limitations in time-frequency resolution and perceptual adaptation, leading to artifacts and inefficiencies in manipulating audio features like pitch and roughness.
Innovation Solution
A signal-adaptive approach that utilizes varying band-pass filters with center frequencies representing the spectral center of gravity, allowing for perceptually meaningful decomposition into carrier and modulation components, enabling efficient manipulation and scalable audio representation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If fixed band-pass filters are used in traditional vocoders, then the device complexity is reduced, but the manufacturing precision of audio signal decomposition deteriorates due to inability to adapt to varying spectral characteristics
Solution Approach 1:
The patent implements dynamic filter bank where the center frequencies and bandwidths of band-pass filters are adaptively adjusted according to the spectral characteristics of the input audio signal. This allows the system to optimize decomposition precision for different audio contents while maintaining manageable complexity through algorithmic control rather than hardware complexity.
Solution Approach 2:
The patent changes the parameters (center frequencies and bandwidths) of the band-pass filters based on the analyzed spectral content of the audio signal. By dynamically modifying these parameters, the system achieves high decomposition precision adapted to the specific audio signal characteristics without requiring a excessively complex fixed filter bank design.
2Productivity
If traditional phase vocoder techniques are used, then the ease of operation is maintained, but the productivity of audio processing deteriorates due to limitations in time-frequency resolution and perceptual adaptation
Solution Approach 1:
The patent segments the audio signal into multiple frequency bands using an adaptive filter bank, where each band is processed independently with optimized parameters. This segmentation approach improves processing efficiency by allowing parallel processing of different frequency regions while adapting to the perceptual characteristics of human hearing in each band.
Solution Approach 2:
The patent introduces dynamic adaptation in the audio processing pipeline by adjusting filter parameters and processing strategies based on the real-time spectral characteristics of the input signal. This dynamic approach enhances productivity by optimizing processing for different audio contents while maintaining operational simplicity through automated control.
3Measurement precision
If fixed resolution filter banks are used, then the device complexity is minimized, but the measurement precision of spectral and temporal information deteriorates due to inability to provide variable time-frequency resolution
Solution Approach 1:
The patent applies local quality by providing different time-frequency resolution characteristics for different frequency bands. Lower frequency bands use wider filters with coarser temporal resolution, while higher frequency bands use narrower filters with finer temporal resolution, matching the perceptual characteristics of human hearing and improving overall measurement precision without excessive complexity.
Data Source
Figure 1A~1B
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Figure 2B
AI summary
An apparatus for synthesizing a parameterized representation of an audio signal comprising a time portion of an audio signal, band pass filter information for a plurality of band pass filters, the band pass filter information indicating time-varying band pass filter center frequencies of band pass filters having varying band widths, which depend on a band pass filter center frequency of the corresponding band pass filter, and having amplitude modulation or phase modulation or frequency modulation information for each band pass filter for the time portion of the audio signal, comprises: an amplitude modulation synthesizer (201) for synthesizing an amplitude modulation component based on the amplitude modulation information; a frequency modulation or phase modulation synthesizer for synthesizing instantaneous frequency of phase information based on the information on a carrier frequency and a frequency modulation information for a respective band width, wherein distances in frequency between adjacent carrier frequencies are different over a frequency spectrum, an oscillator (203) for generating an output signal representing an instantaneously amplitude modulated, frequency modulated or phase modulated oscillation signal (204) for each band pass filter channel; and a combiner (205) for combining signals from the band pass filter channels and for generating an audio output signal (206) based on the signals from the band pass filter channels.