Envelope Shaping for Polyphonic Pitch and Key Modification
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Solution Overview
Problem
Current audio processing techniques fail to effectively modify pre-recorded audio signals to fit new musical contexts while preserving subjective sound quality, particularly in altering pitch, musical key, and scale mode, especially for polyphonic music content.
Innovation Solution
An apparatus and method using a filter bank processor, fundamental determiner, overtone determiner, signal processor, and combiner to identify and modify fundamental and overtone bandpass signals in a correlated manner, preserving the timbre and spectral coherence of the audio signal, thereby enhancing perceptual quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional audio processing techniques are used to modify pitch and key, then the audio signal can be altered to fit new musical contexts, but the subjective sound quality and naturalness deteriorate
Solution Approach 1:
The audio signal is segmented into multiple frequency bands using a filter bank, where each band is processed independently to preserve local spectral characteristics. This segmentation allows selective modification of fundamental frequencies while maintaining the integrity of overtone structures in each band, thereby improving adaptability for pitch and key modification while preserving sound quality.
Solution Approach 2:
Different processing strategies are applied to different frequency bands based on their local characteristics. Fundamental frequency bands undergo pitch transposition processing, while overtone bands are modified to maintain harmonic relationships. This local quality approach ensures that each part of the spectrum is treated appropriately, maintaining naturalness while enabling musical context adaptation.
2Adaptability or versatility
If fundamental and overtone bandpass signals are modified independently, then processing flexibility is improved, but timbre preservation and spectral coherence deteriorate
Solution Approach 1:
The system uses feedback mechanisms where the modified fundamental bandpass signals inform the processing of overtone bandpass signals. The overtone modification is guided by the fundamental signal characteristics to maintain harmonic relationships, ensuring that timbre and spectral coherence are preserved while allowing flexible processing of each band.
Solution Approach 2:
The audio signal is treated as a composite structure consisting of fundamental and overtone components. By processing these components in a coordinated manner rather than as separate independent elements, the system maintains the composite integrity of the original sound while enabling flexible modification. The fundamental and overtone bands are recombined to form the final output, preserving the composite nature of the audio signal.
Data Source
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AI summary
An apparatus for modifying an audio signal comprises an envelope shape determiner, a filterbank processor, a signal processor, a combiner and an envelope shaper. The envelope shape determiner determines envelope shape coefficients based on the a frequency domain audio signal representing a time domain input audio signal and the filterbank processor generates a plurality of bandpass signals in a subband domain based on the frequency domain audio signal. Further the signal processor modifies a subband domain bandpass signal of the plurality of subband domain bandpass signals based on a predefined modification target. The combiner combines at least a subset of the plurality of subband domain bandpass signals containing the modified subband domain bandpass signal to obtain a time domain audio signal. Further, the envelope shaper shapes an envelope of the time domain audio signal based on the envelope shape coefficients, shapes an envelope of the plurality of subband domain bandpass signals containing the modified subband domain bandpass signal based on the envelope shape coefficients or shapes an envelope of the plurality of subband domain bandpass signals based on the envelope shape coefficients before a subband domain bandpass signal is modified by the signal processor to obtain a shaped audio signal.