BCS 151 Lecture 16

Hearing Overview

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What is it good for

communication, navigation, enjoyment, localization, recognition, detecting presence without having to see

Pressure wave

disturbance traveling through a medium → NOT particles moving, but the disturbance moving through the air

• → waves with opposite phases cancel each other out through destructive interference, waves “in-phase” give twice the amplification through constructive interference!

Pure tones

sounds that elicits only a single frequency ex) beeping vs complex speech: multiple frequencies overlapping ex) speech/music

Period

The time for one wavelength to pass a certain point → PITCH

Period (cont, frequency)

-Longer period, lower pitch

-Frequency: how many waves can pass in a period of time

• High: means short period, more waves in 1 second → higher pitch (a lot of waves)

• Low: longer period→ lower pitch (less waves in a second)

Amplitude

How high the wavelength goes → VOLUME

Amplitude (cont)

• Higher amplitude = louder volume

• Amplitude is also referred to as intensity

Amplitude Rules

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Rule 1

The higher the intensity, the greater the loudness (all else being equal)

• → Loudness: the subjective experience of intensity

Rule 2 (IMPORTANT)

the 10dB rule → to double loudness, intensity must increase by 10dB

• 70dB is twice as loud as 60dB

Rule 3

loudness can be affected by signal frequency → mid-frequency signals (1k-4kHz.) are louder than sounds with higher or lower frequencies because we are most sensitive to mid-range

• threshold is lowest for mid-range (daily sounds)

Frequency Rules

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Rule 1

it is easier to distinguish lower frequencies from each other than higher ones

• Weber fraction throwback: as the stimulus intensity increases, the JND also increases

Rule 2

The higher the fundamental frequency, the higher the perceived pitch

• even if F0 – the lowest frequency in the sound – is not present in the stimulus

Rule 3

Since fundamental frequency does not need to be present to hear a pitch, this means the sensation of pitch is based on the SPACING of frequencies (based on fundamental period)

• → can tell a woman is speaking if she is speaking at a 400 600 800Hz (because the spacing is 200!)

Audibility Curve

Depicts the threshold for audibility given signal frequency (lowest for mid-range)

Presbycusis

age-related hearing loss

Timbre

Sound Quality: The difference between 2 sounds, matched for pitch loudness and duration but sound different (timbre) - can tell them apart

• Ex: two different instruments playing the same note → you can tell them apart

TWO PARTS for Timbre Differences

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Spectrum envelope

shows the difference in relative amplitudes of individual frequencies (some just sound louder) - amount of energy instrument uses varies

Amplitude envelope

The beginning vs end of sound waves

• Leading edge: attack (beginning/onset) → biggest effect on timbre

• Trailing: decay(end)- don't hear a difference