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Lecture 21

Lecture 21. Winding Down on the Room-Head stuff. Last Time. Room Acoustics. ?. dB. How the Brain Reacts to certain sounds. Signal Source Issues Room Acoustics. Topics. DONE. Person Instruments (strings and pipes) Space

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Lecture 21

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  1. Lecture 21 Winding Down on the Room-Head stuff

  2. Last Time Room Acoustics ? dB How the Brain Reacts to certain sounds Signal Source Issues Room Acoustics

  3. Topics DONE • Person • Instruments (strings and pipes) • Space • Reflection (and properties of walls), Diffraction or Scattering, Interference, Reverberation • Loudness, Hearing, and the Ear • decibels, the parts of the ear, the cochlea • To the Brain • Hair cells to neurons • Processing • Strange things in the mind • To Music • Dum De Dum Dum! (Beethoven!)

  4. A Basic Musical Question WHAT MAKES TWO OR MORE TONES SOUND WELL TOGETHER?

  5. One Observation • Two close frequencies sounding together produce beats. • Beat frequency is the difference between the two frequencies • fbeat=|f1-f2| • We don’t seem to “like” beats. • Beats exist in the sound itself, it is NOT an ear phenomenon.

  6. Two Tones f2=f1 (In Phase)

  7. Two Tones f2=f1 (Out of Phase)

  8. f1 and f2 close together

  9. Consonance – PURE TONES Octave

  10. Think about the Cochlea • Different frequencies “excite” vibrations at different resonance points along the basilar membrane.

  11. The Frequency Detail

  12. Remember Resonance??

  13. Cochlear Response

  14. Close Frequency Effect one tone sensation

  15. What about a COMPLEX sound?

  16. Single “tone” from a Guitar(or any stringed instrument) Doubling LOG (Frequency) OCTAVE

  17. Two – REAL tones an octave apart Octave They Mesh Nicely !

  18. Two “unrelated” tones Messy

  19. The Fifth and its Harmonics Not AS Messy

  20. Remember the Consonance Experiment with two “single” tones?

  21. Consonance Experiment for two complex tones (overtones) Just What the Greeks Said!

  22. The Strange World of Psychophysics

  23. Strange things can happen in the EAR and in the BRAIN! What about the unexpected???

  24. Salvatore Dali’s Brain

  25. Munch, Edvard TheScream

  26. Strange Stuff • Play 2 tones (f1 and f2) at equal volumes. • Start the two at the same frequency and gradually sweep the f2 frequency up. • A tone LOWER than f1 will be heard my most people! • This is a “difference tone” = |f2-f1| • As f2 approaches 2f1, a rough tone and then something beat-like is heard. • Beats of a “mistuned consonance”.

  27. The “signal” BEATS MISTUNEDCONSONANCE

  28. Two Tones, a Fifth apart f0 = 1/t0=(1/2)f1 f0=(3/2)f1 Fundamental Tracking Subjective Pitch

  29. A Quick Trip(no detail)From the EARto theBrain

  30. The Ear

  31. The Cochlea

  32. Roll It Out

  33. Cochlear Response

  34. The Cochlear Model

  35. Reality • The thickness of the membrane is also a function of position. • My previous model leaves this out. • This actually reverses things a bit. • Do not worry about this mere fact. • Important point is that the cochlea has a resonant frequency that is a function of position along it.

  36. Neuron Connection

  37. Beethoven And that's where music comes from!

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