Transcript ppt file
Localization There are several clues you could use: 1. arrival time 2. phase lag (waves are out of sync) 3. sound shadow (intensity difference)- sound is louder at ear closer to sound source What are some limitations if these are the only cues? Localization • These cues only provide azimuth (left/right) angle, not altitude (up/down) and not distance 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 Localization • What would be the “worst case” scenario for localizing a sound? Pitch and Music Pitch • Pitch is the subjective perception of frequency Period - amount of time for one cycle Frequency - number of cycles per second (1/Period) Air Pressure time -> 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 500 Hz 400 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 Pure Tones are Very Rare in Nature! • What are real sounds composed of? Pure Tones are Very Rare in Nature! • What are real sounds composed of? • Virtually all sounds are composed of several (or many) frequencies all going at once Pure Tones are Very Rare in Nature! • What are real sounds composed of? • Virtually all sounds are composed of several (or many) frequencies all going at once • “Extra” frequencies are called harmonics What are harmonics? imagine a guitar string: up position down What are harmonics? imagine a guitar string: up position down What are harmonics? But more than one frequency can “fit” between the end points up position time -> down What are harmonics? In fact many frequencies can be superposed. up f0 f2 position time -> down f1