the ear as a frequency analyzer reinier plomp, 1976
TRANSCRIPT
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
• Different parts of the Basilar Membrane oscillate at different frequencies
Ear as a Filter Bank
• Pitch and fundamental frequency
• We always perceive the fundamental – even where there is no energy there (demo)
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
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?
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)
Detecting Partials
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.
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)
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
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
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
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
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
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
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Lateral Suppression
• Edges are emphasized
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
Picture Time
• Plaid – 3recurring “Rest Proof Clockwork”
Picture Time
• Venetian Snares' "Look"
Picture Time
• Aphex Twin – Windowlicker FFT