Pitch
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Define PITCH
The perceptual correlate of FREQUENCY
Explain SPECTRAL THEORY OF PITCH PERCEPTION; what biological mechanisms does it involve?
Process involving the inner ear and the basilar membrane that separates a complex tone into its constituent parts which are localised along the membrane’s length
What are the properties of the basilar membrane that allow it process sounds?
• A longitudinal, harmonic complex wave reaches basilar membrane where its vibrations act at a right angle to the basilar membrane • transformed into transverse waves (constituent ‘pure tones’) • Thick base and thin apex that are receptive to high and low frequency vibrations respectively • Sectional thresholds or CRITICAL BANDS along the basilar membrane localise frequencies and split the complex tone into its constituent parts (TONOTOPY) • Each band is stimulated by a certain range frequencies alone (auditory filters)
How does the information from the basilar membrane become a perceived sound?
• Hair cells in the cochlea receive localised signals from the basilar membrane and undergo electrochemical transfer to convert the information into neural signals sent to the brain • The brain receives the broken-down sound and attempts to match its particular pattern/energy distribution to a known template • Once matched, the strata are combined into a single perceptual stream
Explain TEMPORAL THEORY OF PITCH PERCEPTION; what biological mechanisms does it involve? what is PHASE LOCKING?
• PHASE LOCKING: the localised vibrations along the basilar membrane are entrained by nerve impulses • These impulses correspond to peaks of a transverse wave • Separate pure tone transverse waves are communicated to the brain and undergo the template matching process
Explain VOLLEY THEORY
• The impulses of individual nerve cells cannot keep up with wave form that have high periodicity • Multiple nerve cells ‘take it in turns’ to entrain the full periodic sequence between them • Signals undergo AUTOCORRECTIVE ANALYSIS in the brain that combines separate firing patterns into overall periodic stream (where the signal correlates highly with itself)
What is the significance of the range 2 - 4 kHz?
• This is the range at which phase locking breaks down and spectral methods of pitch perception take over • Pitch limit of conventional musical instruments
What are the limits of human hearing?
20Hz - 20kHz
Define PITCH INTERVALS
• AKA ‘melodic intervals’ in Western Music Theory terminology • The perceptual correlate of frequency ratios
What determines the consonance of pitch combinations?
To Western ears, simple integer frequency ratios sound consonant and more complex ratios sound dissonant E.g., an 8ve = 2:1 and a p5th = 3:2, while a maj7 = 15:8
What is OCTAVE EQUIVALENCE?
• Notes an octave apart share an underlying identity of 2:1 • Demonstrated by instruments with an equal temperament • Ratios between pitches retained regardless on starting frequency