by ph00tbag » 11 Dec 2014 11:30
When a linear object like a string (violin) or a column of air (trumpet) vibrates, its harmonics are all whole number ratios of the fundamental, because the geometry of a linear object constrains them to waves within two nodes that force a silently low pressure. With two dimensional objects like drum heads, or the sheets of metal that shape a bell, however, the geometry of the object gives a menagerie of nodes, which all have a variety of pressure tolerances. This means that the harmonic ratios are, well, irrational. Without proper tuning, you can get a sound that is entirely atonal (cymbal), because the chaotic nodes usually suppress the fundamental, and all that's left is the irrational harmonics, but with tuning to get rid of the nodes that suppress the fundamental, you can get a sound that is tonal, but with a vaguely untuned tonal quality (bells).
Frequency modulation introduces irrational harmonics to synth oscillators in much the same way as a two dimensional geometry, especially if your modulator frequency is set to a frequency that is not a whole number ratio of the carrier. At two modulators, you can usually get some very bell-like sounds. In a way, you can think of the modulators as the nodes on a vibrating object. If you keep them low, it's like tuning a drum; they don't drown out the fundamental, so even with the irrational harmonics they produce, it still sounds in tune. You can use a snappy envelope as well, to simulate the sound of striking the bell. Alternately, you can drive the modulators up a bunch to get really atonal, percussive sounds.
Don't bother with making them sound like actual percussion instruments, though. Unless you have a knack for the Calculus in three dimensions, then you can probably figure it out.
