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CU-Boulder PHYS 1240 - Lecture Notes

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1Phys 1240: Sound and MusicLAST: Jeff Merkel on “sound in thestudio”TODAY: Wrapping up - voices,sonograms, …NEXT: Final exam: Sat 7:30-10 PM.See web!Jeff M's office hour is Friday 6-8,Benson Earth Sciences (BESC 185)CT xsurveyWhere do you normally sit?(i.e. for most of this term)A) Front third of the roomB) Middle thirdC) Rear thirdD) BalconiesE) I move a lot!Voice:Consonants:Sudden high pressure.No definite pitch(lips)t (tongue)bpkd(palate)gVoice:Consonants:Some can be sustainedNo definite pitch (not harmonic!)(like "white noise")(lips)th(in) (tongue)vfsth(em)zsh zh(tongue -differentspot) (tongue - furtherback + teeth)2nasal(lips)n (tongue)mng (palate) Some are "mixtures"Say z and open your mouth (becomes a vowel)Close your mouth (becomes an s)vowelsPeriodic (pitch!)Spectrum is harmonicLike a "reed" instrument (vocal cords)Can sustain "ah"Can't sustain "oi" like "oil" formantsFormants:Certain ranges of frequency areenhanced (or suppressed), toform a particular vowel3consider a cylinderWhat are the "resonant frequencies"?ideal spectrum of cylinderof some given size1 kHz2 kHz 3 kHzPossible spectrum of (real) coneof some given size1 kHz2 kHz 3 kHzconsider a "cone"What are the "resonant frequencies"?4Possible spectrum of (real) coneof some given size1 kHz2 kHz 3 kHzPure 250 Hz source (with lots ofharmonics)1 kHz2 kHz 3 kHzsend that 250 Hz sound (with lotsof harmonics) through the cone:1 kHz2 kHz 3 kHz"Formant"send that 500 Hz sound (with lotsof harmonics) through the cone:1 kHz2 kHz 3 kHzSAME Formant5VoiceExploratorium "duck calls"formantsFormants:An "envelope", certain ranges offrequency are enhanced (orsuppressed).The shape of the envelopedetermines what vowel youhear!AM -Amplitude ModulationcarrierSignal (the “envelope”) FM-Frequency modulation6CT 8.3.1Under cover of night, a Girl scoutsignals her friends on a distant hillby alternately dimming andbrightening her flashlight. Thissignal is most accurately describedas..A: Frequency modulation.B: Amplitude modulation.CT 8.3.2Musicians refer to tremolo whenthe loudness fluctuates while thepitch remains unchanged. Is this anexample of…A: Frequency modulation.B: Amplitude modulation.CT 8.3.2bMusicians refer to vibr ato when thepitch is wiggled up and down as yousing. Is this an example of…A: Frequency modulation.B: Amplitude modulation.Violinists can make “excursions”of .2 semitones, 6 times/sec.0.2 semitones-> strength of the modulation6 Hz -> “signal frequency”440 Hz -> “carrier frequency” CT 8.3.3We say that "concert A" correspondsto a frequency of 440 Hz.Does that mean that a flute playingconcert A is emitting low frequencyelectromagnetic radiation which we"hear"?A: Yes, the flute sound is anelectromagnetic wave.B: No, the flute sound is not anelectromagnetic wave.7The semesterat a glance• Production• Propagation• PerceptionThe semesterat a glance• Production• Propagation• PerceptionInstrumentsHarmonicsResonanceWaves and wave propertiesInterference and superpositionSpeedEarLoudness/decibelsPitch/FrequencyCT ex-TG3Which would you pick?A) FlightB) Invisibility8Good luck on the final,And then have a great


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CU-Boulder PHYS 1240 - Lecture Notes

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