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

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There are several clues you could use: Localization

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Left Ear Right Ear Compression Waves

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

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Left Ear Right Ear Compression Waves

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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

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Left Ear Right Ear Compression Waves

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What are some problems or limitations? Localization

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Low frequency sounds arent attenuated by head shadow Localization Left Ear Right Ear Compression Waves Sound is the same SPL at both ears

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

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

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Localization Additional cues:

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

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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

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Auditory Scene Analysis Sounds dont 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?

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

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Auditory Scene Analysis Effect of timing proximity: SlowFast

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

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Auditory Scene Analysis Effect of pitch proximity: closefar

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

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

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Pitch and Music

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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)

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

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

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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

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Chroma Tones that have the same Chroma are octaves apart

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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

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

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

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

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