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Signal Modifiers: Panning and Spatialization


  a1, a2, a3, a4   pan       asig, kx, ky, ifn[, imode[, ioffset]]


Distribute an audio signal amongst four channels with localization control.


ifn – function table number of a stored pattern describing the amplitude growth in a speaker channel as sound moves towards it from an adjacent speaker. Requires extended guard-point.

imode (optional) – mode of the kx, ky position values. 0 signifies raw index mode, 1 means the inputs are normalized (0 - 1). The default value is 0.

ioffset (optional) – offset indicator for kx, ky. 0 infers the origin to be at channel 3 (left rear); 1 requests an axis shift to the quadraphonic center. The default value is 0.


pan takes an input signal asig and distributes it amongst four outputs (essentially quad speakers) according to the controls kx and ky. For normalized input (mode=1) and no offset, the four output locations are in order: left-front at (0,1), right-front at (1,1), left-rear at the origin (0,0), and right-rear at (1,0). In the notation (kx, ky), the coordinates kx and ky, each ranging 0 - 1, thus control the 'rightness' and 'forwardness' of a sound location.

Movement between speakers is by amplitude variation, controlled by the stored function table ifn. As kx goes from 0 to 1, the strength of the right-hand signals will grow from the left-most table value to the right-most, while that of the left-hand signals will progress from the right-most table value to the left-most. For a simple linear pan, the table might contain the linear function 0 - 1. A more correct pan that maintains constant power would be obtained by storing the first quadrant of a sinusoid. Since pan will scale and truncate kx and ky in simple table lookup, a medium-large table (say 8193) should be used.

kx, ky values are not restricted to 0 - 1. A circular motion passing through all four speakers (inscribed) would have a diameter of root 2, and might be defined by a circle of radius R = root 1/2 with center at (.5,.5). kx, ky would then come from Rcos(angle), Rsin(angle), with an implicit origin at (.5,.5) (i.e. ioffset = 1). Unscaled raw values operate similarly. Sounds can thus be located anywhere in the polar or Cartesian plane; points lying outside the speaker square are projected correctly onto the square's perimeter as for a listener at the center.


instr     1
  k1           phasor    1/p3                     ; fraction of circle
  k2           tablei    k1, 1, 1                 ; sin of angle (sinusoid in f1)
  k3           tablei    k1, 1, 1, .25, 1         ; cos of angle (sin offset 1/4 circle)
  a1           oscili    10000,440, 1             ; audio signal..
  a1,a2,a3,a4  pan       a1, k2/2, k3/2, 2, 1, 1  ; sent in a circle (f2=1st quad sin)
               outq a1, a2, a3, a4

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Signal Modifiers: Panning and Spatialization