Auditory Masking Model for Chromagram Key Signature Extraction

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Solution Overview

Problem

Conventional methods for analyzing audio signals struggle to accurately extract melodic, harmonic, and key information due to the overlap of fundamental frequencies and their harmonics, leading to obscured information in chromagrams, especially when higher harmonics mask the fundamental notes.

Innovation Solution

The solution employs an auditory masking model to eliminate inaudible high-frequency components, retaining only the fundamental frequencies and their first few harmonics, which are then converted into a chromagram to represent the essential harmonic structure of the audio, allowing for accurate determination of key signatures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of information

If all tonal components including higher harmonics are included in chromagram extraction, then the chromagram contains complete harmonic information, but higher harmonics mask and obscure the fundamental note information

Engineering Contradiction:

Improveharmonic information completenessVSAvoidfundamental note identification accuracy

Core Design Contradiction:

Loss of informationVSMeasurement precision

Solution Approach 1:

The patent extracts and removes higher harmonics from the chromagram extraction process, retaining only the fundamental frequency components. This is achieved by filtering the spectral peaks to include only those within a specific frequency range around the fundamental frequency, thereby eliminating the masking effect of higher harmonics while preserving the essential harmonic information needed for key signature determination.

Inventive Principle:

Principle #2Taking out (Extraction)

2Measurement precision

If higher harmonics are removed from analysis, then fundamental note information becomes clearer, but harmonic structure representation becomes incomplete

Engineering Contradiction:

Improvefundamental note identification accuracyVSAvoidharmonic structure information

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent applies partial action by including only the necessary portion of harmonic information (fundamental frequency and its immediate harmonics within a defined frequency range) rather than all possible harmonics. This partial extraction is sufficient for accurate key signature determination while avoiding the masking problems introduced by higher harmonics.

Inventive Principle:

Principle #16Partial or excessive action

3Ease of manufacture

If conventional chromagram extraction methods are used, then processing is simple, but key signature determination accuracy is reduced due to harmonic masking

Engineering Contradiction:

Improveprocessing simplicityVSAvoidkey signature determination accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent changes the parameter of frequency range inclusion in chromagram extraction. Instead of including all frequency components, the method specifies a limited frequency range around the fundamental frequency, thereby modifying the extraction parameters to achieve both simplicity and accuracy in key signature determination.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS7910819B2Selection of tonal components in an audio spectrum for harmonic and key analysis

Publication Date: 2011.03.22 KONINKLIJKE PHILIPS NV

AI summary

An audio signal is processed to extract key information by selecting (102) tonal components from the audio signal. A mask is then applied (104) to the selected tonal components to discard at least one tonal component. Note values of the remaining tonal components are determined (106) and mapped (108) to a single octave to obtain chroma values. The chroma values are accumulated (110) into a chromagram and evaluated (112).