02_44_1
additional parameters: none


The instrument plays an endless glissando or Shepard tone, named
after its inventor R.N.Shepard. In this realization the sound
appears to descend infinitely. (Shepard 1964: pp. 2346-53; Risset
1969b: p. 88)

10 parallel units perform the same calculations, but not at the
same time! Amplitude and frequency envelopes of the parallel
building blocks differ in phase by 1/10th of a cycle.  

The frequencies follow an exponential decay, from ifq=3900 to
ifq=3900*2-10. This equals a descent over 10 octaves from the
start to the end of the 120 second note event. 

The phase difference spaces the frequency components exactly one
octave apart. Thus, an octave descent takes 120s/10 = 12 seconds
here. 

The bell-shaped function f71 controls all amplitudes with the
effect of enhancing the frequency trajectory of components in the
mid-frequency range, and attenuating low and high frequency
components. The lowest and highest frequencies are inaudible. 

Interpolating oscillators are recommended to avoid noticeable
noise or discontinuities due to round-off errors. More in general
this holds for all sounds that include frequency modulation.
(Mathews 1969: p. 134; Moore 1977: pp. 26-29, 1985: pp. 326-334)

A sinus starting at 270 degrees (+1,/2) eliminates the additional
step of abusing an audio file to generate a bell-shaped function.
(Risset 1969: #513)

(flowchart)
(.orc and .sco files)

