2. How Can You Localize Sound? Ponder this: –Imagine digging two trenches in the sand beside a lake so that water can flow into them. Now imagine hanging a piece of cloth in the water in each trench. Your job is to determine the number and location and type of every fish, duck, person, boat, etc. simply by examining the motion of the cloth. That’s what your auditory system does! - Al Bregman

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

4. There are several clues you could use: Localization

5. Left Ear Right Ear Compression Waves

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

7. Left Ear Right Ear Compression Waves

8. 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

9. Left Ear Right Ear Compression Waves

10. 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 3.Head shadow Localization

11. Arrival Time Phase Lag Head Shadow Interaural Timing Differences (ITD) Interaural Intensity Difference (IID)

12. What are some problems or limitations? Localization

13. Low frequency sounds aren’t attenuated by head shadow because sound bends around the head with little loss of amplitude Localization Left Ear Right Ear Compression Waves Sound is the same SPL at both ears

14. Low frequency sounds aren’t attenuated by head shadow Your brain preferentially uses ITD cues for low-frequency sounds Localization

15. High frequency sounds have ambiguous phase lag because more than one wavelength “fits” between the ears Localization Left Ear Right Ear Left Ear Right Ear Two locations, same phase information!

16. High frequency sounds have ambiguous phase lag Your brain preferentially uses IID cues for high-frequency sounds Localization

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

18. Localization Additional cues:

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

20. 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

21. Localization What would be the “worst case” scenario for localizing a sound?

22. Pitch and Music

23. 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)

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

25. 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…

26. 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

27. Chroma Tones that have the same Chroma are octaves apart

28. 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

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

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

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

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