Auditory Masking and Critical Bands

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Explain how the asymmetry of the traveling wave on the basilar membrane contributes to the upward spread of masking. Why does this asymmetry result in higher frequencies being more easily masked than lower frequencies?

The asymmetry of the traveling wave means that the excitation pattern on the basilar membrane has a sharp cutoff on the low-frequency side and a gradual tail on the high-frequency side. Because of this shape, a low-frequency masker can more effectively activate the regions of the basilar membrane that respond to higher frequencies, leading to the upward spread of masking.

Describe the relationship between critical bandwidth and the perception of complex sounds. How does the width of the critical band affect the ability to distinguish between two closely spaced frequencies or to perceive the timbre of a complex tone?

Narrower critical bands allow for finer frequency discrimination, enhancing the ability to distinguish closely spaced frequencies and perceive subtle differences in timbre by more accurately resolving individual components of a complex tone. Wider critical bands reduce frequency discrimination.

Explain how binaural squelch improves speech intelligibility in noisy environments. What are the underlying mechanisms that allow the auditory system to enhance the signal-to-noise ratio when processing sounds with two ears?

Binaural squelch enhances speech intelligibility in noise by exploiting differences in the signal and noise at each ear. It relies on mechanisms that process interaural time differences (ITDs) and interaural level differences (ILDs) to suppress noise that is uncorrelated or out-of-phase between the ears, effectively improving the signal-to-noise ratio for the target speech.

Describe how the head-related transfer function (HRTF) affects our ability to localize sound sources, particularly at higher frequencies. What specific acoustic cues are modified by the HRTF, and how do these modifications contribute to our perception of a sound's location in three-dimensional space?

<p>The HRTF alters the spectral characteristics of sounds, particularly at higher frequencies, by introducing frequency-dependent amplifications and attenuations that vary with the direction of the sound source. These modifications create unique acoustic cues that the auditory system uses to determine the elevation and front-back location of a sound, complementing the interaural time and level differences used for lateralization.</p> Signup and view all the answers

Explain how the non-linear growth of loudness, as described by Steven's power law, influences our perception of sound intensity at different sound pressure levels (SPLs). How does the relationship between perceived loudness and SPL change as the overall intensity of a sound increases or decreases?

<p>Steven's power law suggests that loudness grows as a power function of sound intensity, with the exponent being less than one. At lower SPLs, loudness grows more rapidly than at higher SPLs due to the cochlear amplifier. This means that small changes in intensity are more noticeable at lower levels, while larger changes are required to produce the same change in perceived loudness at higher levels.</p> Signup and view all the answers

Flashcards

Masking

The obscuring of one sound by another.

Critical Band

The range of frequencies around a tone that contribute to masking.

Binaural Summation

A phenomenon where the perception of a signal changes when both ears receive the signal compared to only one ear.

Sone Scale

A subjective unit of loudness, where 1 sone is the loudness of a 1 kHz tone at 40 dB SPL.

Signup and view all the flashcards

Phon Scale

A logarithmic scale of loudness level where equal phon values are perceived as equally loud.

Signup and view all the flashcards

Study Notes

Masking relies on the critical band.
Masking is a linear process.
Temporal masking includes both backward masking, where the masker follows the probe, and forward masking, where the probe follows the masker.
Psychophysical tuning curves are determined using a steady probe with varying masker level and frequency, mirroring neural tuning curves.
These curves reflect the asymmetry of the traveling wave.
Upward spread of masking impacts the audibility of higher frequencies.

Critical Bands

Critical band refers to the minimum bandwidth of masking noise needed to mask a probe tone.
The width of this band is known as the equivalent rectangular bandwidth.
Frequencies closest to the probe frequency are most effective in masking, following a normal distribution.
Notched-noise and band-widening experiments are used to determine critical bands.
Higher frequencies have larger critical bandwidths than lower frequencies, approximately 1/3 octave wide.
Wider critical bands result in less ringing.
The auditory system uses an auditory filter bank, which is made up of a series of band-pass filters, numbering about 24 critical bands.
Frequency specificity, created by these filters, is crucial for sound processing and loudness perception.
Waves in multiple critical bands contribute to greater loudness.

Binaural Hearing

Binaural hearing involves binaural summation (3 dB boost), squelch, and redundancy.
It is essential for localization and lateralization of sound.
Interaural time differences (ITD) are important for low-frequency sounds.
Interaural intensity differences (IID) are important for high-frequency sounds.
Binaural masking level differences occur when altering signal and noise phase/correlation, leading to variable release from masking.

Intensity Coding/Loudness

The head transfer function, outer ear/external auditory meatus (OE/EAM) resonance and shaping, and middle ear (ME) mass/stiffness contribute to how we hear best in the mid frequencies.
Low frequencies require a higher threshold.
The phon scale is an equal loudness scale based on 1000 Hz.
For example, 20 phons is equal in loudness to 1000 Hz presented at 20 dB SPL.
Faster loudness growth, paired with higher thresholds, occurs at low frequencies.
The sone scale defines loudness ratio, basing it on a 1000 Hz tone at 40 dB SPL being 1 sone.
A 10 dB SPL increase results in a doubling of loudness, coming close to Weber’s Law.
Below 40 dB, a 6 dB SPL increase doubles loudness, due to the cochlear amplifier and Steven’s law.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explanation of auditory masking, focusing on critical bands, temporal masking, and psychophysical tuning curves. Describes how the critical band is the minimum bandwidth of noise needed to mask a sound. Also discusses notched-noise, band-widening experiments, and upward spread of masking.