Harmonic Series and Spectrograms By Jordan Kearns (W&L ‘14) & Jon Erickson (still here )
220 Hz (A3) Why do they sound different? Instrument 1 Instrument 2 Sine Wave Why do they sound different?
Waveform Piano Guitar Sine Wave
Overtones and Music Perception Overtones occur at integer multiples of the fundamental frequency when an object vibrates. The addition of these tones at regular intervals is musical to the human ear. Example: Fundamental (1st Harmonic): 220Hz 1st Overtone (2nd Harmonic): 440Hz 2nd Overtone (3rd Harmonic): 660Hz Video produced by Brandon Pletsch Univ. of Georgia Medical School URL: https://www.youtube.com/watch?v=PeTriGTENoc
Frequency Spectrum Piano Guitar
Modes of Vibration: Standing Waves
Harmonic Motion in Guitar
Frequency Decomposition: Pure Sine Wave T = 2ms f = 1/T f = 500Hz
Frequency Decomposition: Pure Sine Wave T = 1ms f = 1/T f = 1000Hz
Composite Wave I
Composite Wave II
Waveform Piano Guitar Sine Wave
Spectrogram: Piano
Piano: Component Sine Waves Microphone Signal Amplitude Time
Piano: Component Sine Waves Composite Wave (From Previous Slide) Original Piano Wave Look how close with only three sine waves!!!
Fourier Series and Superposition Any wave (sound) can be mathematically represented as some combination of sine waves. Wave= SineWave1 + SineWave2 + SineWave3+… 𝑓 𝑡 = 𝑎 1 sin 2𝜋∗𝑓∗𝑡 + 𝑎 2 sin 2𝜋∗2𝑓∗𝑡 + 𝑎 3 sin 2𝜋∗3𝑓∗𝑡 +… Fourier Series = Frequency Spectrum lets us see the component frequencies that make up the unique sound!
Why you should change strings A quick experiment with a spectrogram Old New
Piano C chord (2nd inversion) C major chord G4 (388) E5 (657) C5 1171 G5 (775) 1314 1564
Frequency Spectra for Different Instruments Same pitch played, but TIMBRE is entirely unique