11.3 Pitch perception and critical bands

Pitch perception is a fascinating aspect of how we experience sound. It's not just about frequency; factors like intensity and timbre play a role too. Understanding pitch helps us grasp how our ears and brain work together to interpret the world of sound around us.

Critical bands are like the building blocks of how we process sound frequencies. They explain why some sounds mask others and how we can pick out specific voices in a noisy room. This concept is crucial for understanding how our auditory system breaks down complex sounds.

Pitch Perception

Explain the concept of pitch and its relationship to frequency

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  Pitch Perception – Introduction to Sensation and Perception View original

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• Pitch measures subjective perception of sound frequency and psychologically correlates to fundamental frequency
• Higher frequency generally leads to higher perceived pitch but relationship not linear
• Intensity, duration, and spectral content influence pitch perception (loudness, note length, timbre)

Describe the difference between simple and complex tones

• Simple tones consist of single frequency produced by pure sine waves (tuning forks)
• Complex tones composed of multiple frequencies including fundamental and harmonics (musical instruments, voice)

Explain the place theory of pitch perception

• Different frequencies excite specific locations along basilar membrane (high frequencies basal region, low frequencies apical region)
• Tonotopic organization maps frequencies to cochlea locations preserved in auditory pathway (cochlea to auditory cortex)
• Place theory limited in explaining low frequency pitch perception requires additional mechanisms (temporal coding)

Critical Bands

Define critical bands and their significance in auditory perception

• Critical bands represent frequency range processed by same hair cell group measuring auditory system frequency resolution
• Critical bands form basis for auditory masking, influence loudness perception, and aid sound localization (cocktail party effect)

Describe the relationship between critical bands and the basilar membrane

• Basilar membrane exhibits tonotopic organization with gradual stiffness and width changes
• Each critical band corresponds to ~1.3 mm constant distance along basilar membrane
• Lower frequencies have wider critical bands while higher frequencies have narrower bands (frequency-dependent resolution)

Explain the concept of the Bark scale and its relation to critical bands

• Bark scale measures psychoacoustic pitch based on critical bands (1 Bark ≈ 1 critical bandwidth)
• 24 Bark units cover audible frequency range (20 Hz to 20 kHz)
• Non-linear Hz to Bark conversion: $z = 13 * arctan(0.00076f) + 3.5 * arctan((f/7500)^2)$ where $z$ is Bark value and $f$ is frequency in Hz
• Bark scale applied in audio compression, speech recognition, and psychoacoustic modeling (MP3, voice assistants)