Tutorials and Topics - Peabody Computer Music

Tutorial 22MIDI Control:PanningTherefore, we"ll map the range of MIDI values 0 to 127 onto the range 0 to 0.25, and usethe result as an angle for looking up the cosine and sine values.Technical detail: As the sound source travels on a hypothetical arc from 0˚to 90˚ ( 1 /4 cycle around a circle with the listener at the center), the cosine ofits angle goes from 1 to 0 and the sine of its angle goes from 0 to 1. At allpoints along the way, the square of the cosine plus the square of the sineequals 1. This trigonometric identity is analogous to what we are trying toachieve—the sum of the squares of the amplitudes always equaling thesame intensity—so these values are a good way to obtain the relativeamplitudes necessary to simulate a constant distance between soundsource and listener.• Double-click on the p "constant distance xfade" object to open its Patcher window.MIDI values 0 to 127 are mapped onto 1/4 cycle of cosine and sine functionsOnce again we need to treat MIDI values greater than 64 differently from those less thanor equal to 64, in order to retain 64 as the “center” of the range. Once the MIDI value ismapped into the range 0 to 0.25, the result is used as a phase angle two cycle~ objects, onea cosine and the other (because of the additional phase offset of 0.75) a sine.• Close the subpatch window. Choose “Equal Distance Crossfade” from the umenu.Listen to the sound while panning it slowly from one channel to the other.Is the difference from the linear crossfade appreciable? Perhaps you don"t care whetherthe listener has the impression of movement in an arc when listening to the sound beingpanned. But the important point is that the equal distance method is preferable if only182