Notes

Synthesis

  • Make a sound: contrast with analysis, effects

  • Many popular approaches

    • Wavetables

    • Additive / Subtractive

    • Frequency Modulation

    • Some really fancy stuff

Notes

  • A "note" is a sound with a fixed frequency

  • Briefly: Western music uses a "12-tone scale"

    • Remember that the ear hears frequency on log / exp scale

    • An "octave" is a frequency that is twice some other frequency

    • We divide an octave into 12 parts: with a base frequency f, we have

      $$ \textrm{note}_i(f) = f \cdot 2^{i/12} $$

  • For example:

    \begin{eqnarray*} \textrm{note}_{0}(f) &=& f \\ \textrm{note}_{12}(f) &=& 2f \\ \textrm{note}_{-24}(f) &=& \frac{f}{4} \end{eqnarray*}

  • There is a bunch of music theory here for future

Key Numbers, Note Names

  • For Western scales, the base frequency is 440Hz, because reasons

  • We can use a numbering based on piano keys as a standard: MIDI "key number"

  • In MIDI 440Hz A is key 69; we call this the A in "octave 4" or A4

  • We give the notes letter names with a possible "sharp" or "flat" modifier

      Key   Freq    Name    Octave
      69    440     A       4
      70    466.16  B♭/A♯
      71    493.88  B
      72    523.25  C
      73    554.37  D♭/C♯
      74    587.33  D
      75    622.25  E♭/D♯
      76    659.26  E
      77    698.46  F
      78    739.99  F♯/G♭
      79    783.99  G
      80    830.61  A♭/G♯
      81    880     A       5
    
  • The "why" of all this is a future lecture

Note Timing

  • Notes start at a particular time, have a particular duration (how long they continue to play)

  • For now, will think of this as an "on time" and "off time" for the note

  • There's a whole complicated theory here, but we don't need it yet

  • Typically start times are 4 to 30ms apart or thereabouts, durations are 4ms and up

  • Notes may overlap: "polyphony". Some instruments (including some synths) are monophonic: one note at a time, so start of next note is end of current

Last modified: Thursday, 30 April 2020, 6:34 PM