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The Ear As a Frequency Analyzer

The Ear As a Frequency Analyzer. Reinier Plomp, 1976. Overview. Ear As a Filter Bank How We Identify Sounds Detecting Partials: Multiple Approaches Masking Inverse Masking: Pulsation Threshold Lateral Suppression Conclusions. Ear as a Filter Bank.

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The Ear As a Frequency Analyzer

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  1. The Ear As a Frequency Analyzer Reinier Plomp, 1976

  2. Overview • Ear As a Filter Bank • How We Identify Sounds • Detecting Partials: Multiple Approaches • Masking • Inverse Masking: Pulsation Threshold • Lateral Suppression • Conclusions

  3. Ear as a Filter Bank • Different parts of the Basilar Membrane oscillate at different frequencies

  4. Ear as a Filter Bank • Pitch and fundamental frequency • We always perceive the fundamental – even where there is no energy there (demo)

  5. How We Identify Sounds • Trumpet at one octave above Middle C (523.25 Hz) and it’s Fourier transform • Timbre: the psychoacoustician's waste-basket

  6. How We Identify Sounds • Ohm’s Acoustic Law: • Each tone of different pitch in a complex sound originates from the objective existence of that freq in the Fourier analysis of the acoustic wave pattern • So, can we always hear the partials?

  7. Detecting Partials • Helmholtz: • to determine whether a partial is present in a complex sound, listen first to a tone of the same pitch as the partial, and then listen to the target • Early difficulties: • Was this partial present? • How many tones made up this tone? • Three position switch • Harmonic and inharmonic partials (demo)

  8. Detecting Partials

  9. Detecting Partials • Identification of partials depends on: • Frequency • Frequency Separation Figure: Frequency difference between the harmonics of a complex tone, required to hear them separately, as a function of frequency.

  10. Critical Bandwidth • The difference in frequency between two pure tones at which the sensation of "roughness" disappears and the tones sound smooth is known as the critical band • When two such frequencies lie within what has been termed a critical bandwidth, sensory dissonance is experienced • (Demo)

  11. Masking • Masking: • Where one sound prevents another from becoming audible • By playing at the same time (simultaneous masking) • By playing beforehand (forward masking) • Applications to digital watermarking

  12. Masking • Masking Threshold • The minimal sound pressure level of a sinusoidal probe tone required to detect this tone in the presence of a masking stimulus • Masking Pattern • The dependence of the masked threshold upon the frequency of the probe tone

  13. Masking and “The Auditory Filter” • Simultaneous Masking Results • The closer the mask frequency is to the target tone, the louder the target must be • Problems close to the target tone • Beats (demo) • Combination tones (demo) • “Noise Mask” alleviates these problems

  14. Pulsation aka “Inverse Masking” • “Inverse Masking” • Uses a non-simultaneous probe tone which is longer in duration than the brief tone bursts in forward masking. Makes an nonexistent inaudible stimulus seem audible • Think of it visually: • Figure vs. Ground • Occlusion

  15. Pulsation Threshold • The maximal level at which the probe tone still sounds continuous • The general shape of the pulsation threshold pattern for a single pure tone doesn’t differ from the masking pattern, but for those probe tones coinciding in frequency with the harmonic, the threshold is much lower: it’s easier to hear it as pulsating

  16. Lateral Suppression • This can be considered lateral inhibition or lateral suppression • Like in vision, the edges of the filter (mach bands) can be emphasized by contrast phenomena • Non-simultaneous masking should be used; the masking contour will not show up when both the mask and the probe are subjected to the suppression process

  17. Lateral Suppression • Edges are emphasized

  18. Conclusions • The ear can identify the partials of a complex sound, as long as the frequencies are separated by more than 15 to 20%, with a minimal frequency distance of about 60 Hz • Non-simultaneous masking results in lateral suppression • Auditory bandwidth will change depending on whether it’s measured with non-simultaneous probes or simultaneous probes

  19. Picture Time • Plaid – 3recurring “Rest Proof Clockwork”

  20. Picture Time • Venetian Snares' "Look"

  21. Picture Time • Aphex Twin – Windowlicker FFT

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