EU6D 2015-02-04 Noise and Beats

Mr. Weisenfeld talks about Noise and Beats from Hecht Chapter 11.

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EU6D 2015-02-04 Noise and Beats

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Mr. Weisenfeld talks about Noise and Beats from Hecht Chapter 11.
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  1. EU 6.D:  Interference and superposition lead to standing waves and beats.

    Slide 1 - EU 6.D: Interference and superposition lead to standing waves and beats.

    • Mr. Weisenfeld
  2. Slide 2

    • Hecht, Section 11.9, pg 395
  3. What do we mean by nonperiodic?

    Slide 3 - What do we mean by nonperiodic?

  4. Let’s compare “white noise” and “pink noise”

    Slide 4 - Let’s compare “white noise” and “pink noise”

    • On the next two slides you have 2 minute samples of
    • White noise
    • Pink noise
    • Adjust the volume how you like and then take a listen.
    • What I want you to think about is which noise seems to have a lot of low frequency content versus high frequency content.
    • Also think about which noise you feel like you could listen to for an extended period of time, many people do this for relaxation.
  5. White Noise

    Slide 5 - White Noise

    • Adjust volume as needed, I turned it down.
  6. Pink Noise (As Opposed to White Noise)

    Slide 6 - Pink Noise (As Opposed to White Noise)

    • Pink and White Noise have different frequency spectra.
    • The amount and frequency of the sounds that make up these “noises” are different.
    • Adjust volume as needed, I turned it down.
  7. A Little Survey on White and Pink Noise

    Slide 7 - A Little Survey on White and Pink Noise

  8. Visualizing White Noise

    Slide 8 - Visualizing White Noise

    • (a) is gauge pressure, since sound is a compression wave, we are plotting the pressure at a point as the wave passes by in time.
    • (b) Breaking down that signal into the frequencies it would take to produce it.
    • It is an equal mix of sounds at all audible frequencies.
  9. Pink Noise, on the other hand.

    Slide 9 - Pink Noise, on the other hand.

    • Here is how they differ in spectrum, i.e. the intensity or amount of each sound frequency.
  10. Galileo on sound

    Slide 10 - Galileo on sound

    • Hecht, Section 11.9, pg 395
  11. A Siren

    Slide 11 - A Siren

    • By “tapping on air”, i.e. interrupting a flow of air in a regular way, a siren is created.
    • I don’t think police car sirens are like this anymore, but old-fashioned air-raid sirens are exactly like this, only at a bigger scale.
    • Click to hear a smaller siren.
    • Hecht, Section 11.9, pg 396
  12. Can you hear the beats?  (Pulsations of sound?)

    Slide 13 - Can you hear the beats? (Pulsations of sound?)

    • Volume is turned low, turn up until you are comfortable.
  13. A formula to remember.

    Slide 16 - A formula to remember.

  14. Hands on with Beats.

    Slide 18 - Hands on with Beats.

    • In the next slide you get to change the frequencies of two waves.
    • A couple of things to try
    • One really big, one really small
    • Close together, but small
    • Close together, but big
    • Can you see the beats?
    • When do you not see the beats? Why?
  15. Slide 20

    • Hecht, Section 11.9, pg 397, Example 11.11
  16. Slide 21

    • Hecht, Section 11.9, pg 397, Example 11.11
  17. A final word, everything makes sound, not everything makes music.

    Slide 22 - A final word, everything makes sound, not everything makes music.

    • Hecht, Section 11.9, page 397