All you have is a pair of instruments (basilar membranes) that measure air pressure fluctuations over time Localization

There are several clues you could use: Localization

Left Ear Right Ear Compression Waves

There are several clues you could use: 1 arrival time - sound arrives first at ear closest to source Localization

Left Ear Right Ear Compression Waves

There are several clues you could use: 1.arrival time 2.phase lag (waves are out of sync) - wave at ear farthest from sound source lags wave at ear nearest to source Localization

Left Ear Right Ear Compression Waves

What are some problems or limitations? Localization

Low frequency sounds aren’t attenuated by head shadow Localization Left Ear Right Ear Compression Waves Sound is the same SPL at both ears

High frequency sounds have ambiguous phase lag Localization Left Ear Right Ear Left Ear Right Ear Two locations, same phase information!

These cues only provide azimuth (left/right) angle, not altitude (up/down) and not distance Localization Left Ear Right Ear Azimuth

Localization Additional cues:

Localization Additional cues: Head Related Transfer Function: Pinnae modify the frequency components differently depending on sound location

Localization Additional cues: Room Echoes: For each sound, there are 6 “copies” (in a simple rectanguluar room!). Different arrival times of these copies provide cues to location of sound relative to the acoustic space

Auditory Scene Analysis Sounds don’t happen in isolation, they happen in streams of changing frequencies How does the system group related auditory events into streams and keep different streams separate?

Auditory Scene Analysis Solving this problem is called Auditory Scene Analysis One important principle is proximity –in pitch, time, or spatial location

Auditory Scene Analysis Effect of timing proximity: SlowFast

Auditory Scene Analysis Effect of timing proximity: Pitch Do you hear this? Pitch Or this? SlowFast

Auditory Scene Analysis Effect of pitch proximity: closefar

Auditory Scene Analysis Effect of pitch proximity: Pitch Do you hear this? Pitch Or this? closefar

Auditory Scene Analysis Effect of proximity: –auditory system groups together events that happen close together in time and frequency

Pitch and Music

Pitch Pitch is the subjective perception of frequency time -> Air Pressure Period - amount of time for one cycle Frequency - number of cycles per second (1/Period)

Pitch Pure Tones - are sounds with only one frequency f = 400 hz f = 800 hz

Tone Height Tone Height is our impression of how high or low a sound is but there’s something more to our impression of how something sounds than just its tone height…

Chroma Tone Chroma is the subjective impression of what a tone sounds like Notes that have the same Chroma sound similar 400 hz 500 Hz 800 Hz

Chroma Tones that have the same Chroma are octaves apart

Chroma chroma is best represented as a helix chroma repeats every octave tones with the same chroma are above or below each other on a helix

Chroma Tones that are octaves apart have the same chroma one octave is a doubling in frequency

Chroma frequency is determined (in part) by location of stimulation on the basilar membrane

Chroma frequency is determined (in part) by location of stimulation on the basilar membrane but that relationship is not linear (it’s logarithmic)

Chroma doublings of frequency map to equal spacing on the basilar membrane