a Lowpass Filter is usually used to remove the higher, brighter tones from a sound, leaving it sounding darker, or 'warmer'. at it's simplest, it works something like this:
[audio in] =>=+===========>===============>==================+=>= [audio out]
| |
^ v
| |
+=<=[volume reduction]=<=[slight time delay]=<=+
it takes the sound, delays it slightly (i'm talking less than a thousandth of a second), turns the volume down, brings it back and adds it to itself. this makes the signal of the sound at any given millisecond a little more similar to it's position the millisecond before. looking at a waveform of a lowpassed sound and comparing it to the original, the lowpassed singnal looks like it's having trouble moving as quickly; it's abrupt corners are rounded, lethargic.
so rather than using the filter to change the tone of sound, i thought i'd see if you could use it to make a change in position of something visual seem heavier, like it was having trouble tracking those tight corners like the waveform. i used PureData's filters and openGL graphics to make this:
at first it was just the sphere, 3 noise generators (one for it's x, y, and z position), and 3 lowpass filters (all set to something like .05hz). i think it looks like it has momentum. :)
then it turned into screwing around; i took the sphere's position, branched it to (i think) 60 different grouped xyz sets, lowpassed it again (lower frequencies for the bigger particles), made an 'orbit' rotation, and then screwed around with colored lights, added mouse tracking, and a few other bells + whistles.
