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Computer Sound Synthesis 2

Computer Sound Synthesis 2. MUS_TECH 335 Selected Topics. Filter: a frequency-dependant attenuator It enhances some frequencies and diminishes others. Amplitude Response. a. no filtering. f. low. high. a. filtering. f. low. high. Basic Types of Amplitude Response. f. f. low-pass.

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Computer Sound Synthesis 2

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  1. Computer Sound Synthesis 2 MUS_TECH 335 Selected Topics

  2. Filter: a frequency-dependant attenuator It enhances some frequencies and diminishes others.

  3. Amplitude Response a no filtering f low high a filtering f low high

  4. Basic Types of Amplitude Response f f low-pass high-pass f f band-pass band-reject

  5. a 1.0 3 dB .7071 stop-band pass-band f fc cutoff frequency (half power point or -3 dB point) a 1.0 .7071 bandwidth f fc center frequency

  6. Source/Filter Interaction Source f transfer function Filter f Result f

  7. How are they perceived? resonance anti-resonance Induced pitch

  8. Special Signals time frequency sine t f dc t f Nyquist t f 1/2 SR impulse t f

  9. Impulse Response output input filter 1., 0., 0., 0., .1, .6, .7, .4, -.3, -.1, time t t frequency f f

  10. z-1 z-m Graphic Symbols signal flow multiply a add + unit delay input x(nT) y(nT) output delay of m samples

  11. Digital Filters Two Types non-recursive feed forward “notches” FIR in k a out z-1 out recursive feed back “peaks” IIR in k z-1 a first-order filters

  12. spectral features recursive (poles) non-recursive (zeros) filter type acoustic analog stored energy resonance cancelled energy anti-resonance

  13. non-recursive x(nT) k a y(nT) z-1 a = 1 a = -1 x(nT) 1 1 1 1 1 y(nT) 1 2 2 2 2 x(nT) 1 -1 1 -1 1 y(nT) 1 0 0 0 0 x(nT) 1 1 1 1 1 y(nT) 1 0 0 0 0 x(nT) 1 -1 1 -1 1 y(nT) 1 -2 2 -2 2 n 0 1 2 3 4 n 0 1 2 3 4

  14. recursive y(nT) x(nT) k z-1 b b = .9 x(nT) 1 1 1 1 1 1 y(nT) 1.0 1.9 2.7 3.4 4.1 4.7 x(nT) 1 -1 1 -1 1 -1 y(nT) 1.0 -.10 .91 -.18 .84 -.25 n 0 1 2 3 4 5

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