what do we hear? sound is a compression wave - it only “looks” like a wave if we plot air...
TRANSCRIPT
What do we hear?
• Sound is a compression wave - it only “looks” like a wave if we plot air pressure against time
time ->
Air Pressure
Period - amount of time for one cycle
Frequency = number of cycles per second (1/Period)
Sensing Vibrations
• Inside the cochlea is the basilar membrane• Movement of the oval window causes ripples
on the basilar membrane
Hearing• Detection • Loudness • Localization• Scene Analysis • Music• Speech
Detection and Loudness
• Sound level is measured in decibels (dB) - a measure of the amplitude of air pressure fluctuations
Detection and Loudness
• Sound level is measured in decibels (dB) - a measure of the amplitude of air pressure fluctuations
• dB is a log scale - small increases in dB mean large increases in sound energy
Detection and Loudness
• Sound level is measured in decibels (dB) - a measure of the amplitude of air pressure fluctuations
• dB is a log scale - small increases in dB mean large increases in sound energy
• We have a dynamic range that is a factor of 7.5 million!
Detection and Loudness
• minimum sound level necessary to be heard is the detection threshold
Detection and Loudness
• detection threshold depends on frequency of sound:
• very high and very low frequencies must have more energy (higher dB) to be heard
• greatest sensitivity (lowest detection threshold) is between 1000 hz to 5000hz
Detection and Loudness
• Detection can be compromised by a masking sound
• even masking sounds that are not simultaneous with the target can cause masking (forward and backward masking)
Detection and Loudness
• Loudness is the subjective impression of sound level (and not identical to it!)
Detection and Loudness
• For example, tones of different frequencies that are judged to be equally loud have different SPLs (dB)
Detection and Loudness
• Hearing loss due to exposure to high-intensity sounds (greater than 100 dB) is frequency-specific and can last many hours
Detection and Loudness
• Incidence of noise-related hearing loss is increasing dramatically• iPods and other “earbud” music players are thought to be partly
responsible• How loud is an iPod?
– maximum volume is approximate but is somewhere between 100 dB (hearing damage in about 2 hours) to 115 dB (hearing damage in about 15 minutes)
• Consequences: difficulty understanding speech, tinnitus, deafness • Your perception of loudness adapts so it’s hard to tell how loud your
iPod is - LOCK THE VOLUME ON YOUR iPOD!