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GEN Routines: Waveshaping


  f  #  time  size  3  xval1  xval2  c0  c1  c2  .  .  .  cn   


This subroutine generates a stored function table by evaluating a polynomial in x over a fixed interval and with specified coefficients.


size – number of points in the table. Must be a power of 2 or a power-of-2 plus 1.

xval1, xval2 – left and right values of the x interval over which the polynomial is defined (xval1 < xval2). These will produce the 1st stored value and the (power-of-2 plus l)th stored value respectively in the generated function table.

c0, c1, c2, ... cn – coefficients of the nth-order polynomial

c0 + c1x + c2x2 + . . . + cnxn

Coefficients may be positive or negative real numbers; a zero denotes a missing term in the polynomial. The coefficient list begins in p7, providing a current upper limit of 144 terms.


The defined segment [fn(xval1), fn(xval2)] is evenly distributed. Thus a 512-point table over the interval [-1,1] will have its origin at location 257 (at the start of the 2nd half). Provided the extended guard point is requested, both fn(-1) and fn(1) will exist in the table.

GEN03 is useful in conjunction with table or tablei for audio waveshaping (sound modification by non-linear distortion). Coefficients to produce a particular formant from a sinusoidal lookup index of known amplitude can be determined at preprocessing time using algorithms such as Chebyshev formulae. See also GEN13.


  f 1 0 1025 3 -1 1 5 4 3 2 2 1

This calls GEN03 to fill a table with a 4th order polynomial function over the x-interval -1 to 1. The origin will be at the offset position 512. The function is post-normalized.

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GEN Routines: Waveshaping