By Trent Rentsch
Last month we began a journey into the world of creating sounds by looking at how Mother Nature does it, how changes in air pressure cause vibrations, big and small, faster and slower, which our ears perceive as sound. There are a couple more points about sound in the real world we need to cover this month before we look at how to synthesize our own audio world.
We ended last month talking about sine waves, which are the building blocks that make each sound unique. The easiest way to describe how they work is a “visual” example. Imagine someone strumming a guitar. The vibration of each string causes a different group of sine waves… that is obvious. Less obvious are the vibrations of every other piece of the guitar, however extreme or subtle. Some of them start sooner, some later, some are at different frequencies, some louder, some softer. Then there are the other sine waves that appear as other materials in the area are affected by the guitar’s vibrations and start some of their own. This is why the same guitar played by the same person will have a different sound depending on the room it is played in.
All of the sine waves that make up that strum (or any other musical sound, for that matter) are called “partials.” The lowest partial is considered the “fundamental,” and the frequencies of the rest of the sine waves are whole number multiples of each other, called “harmonics.” Don’t worry, there won’t be a quiz on this… this month, anyway. It will come into play as we begin building sounds, if you’re designing a musical sound. If you’re only interested in making noise, the frequencies are more or less random, and are not so surprisingly called… “noise.” Again, we’ll talk more about this when we actually begin building our own sounds. Just remember that the timbre or tone “color” of each sound depends on what partials are there and how loud they are.
One more component of sine waves we need to touch on is “phase.” I mentioned that sine waves move up and down, and one complete motion from zero, up, down and back to zero again is called a “cycle.” Cycles are measured in degrees, 360 degrees is one full cycle. If you have two sine waves of the same frequency and amplitude playing together and they’re moving up and down at the same time, you basically end up with a sound that’s twice as loud. However, if the two are moving up and down opposite of each other, you get phase cancellation… or, no sound. We’ve all heard stereo tracks that are “out of phase,” so you know how it “sounds hollow,” and some audio disappears all together.
As we’ve seen, most sounds are made up of a lot more than 2 sine waves, however, and it’s not uncommon in a sound for different sine waves to be in and out of phase, but because they are at different frequencies, the phase cancellation more or less becomes part of the timbre of the sound… in fact, it is another useful tool in synthesis that we’ll be looking at more later. This type of phase cancellation is called “beating,” and it actually adds (to our ears, at any rate) new components to the sound that are called “difference tones.”
When you consider that each sound is built of many sine waves, all bouncing up and down and around one another, sometimes building more components to the sound — all of which vibrate our ear drums, which stimulates the nerves that run the information up the flag pole to our brain where it’s understood as sound — it is mind boggling that anyone could conceive of a machine that could duplicate a sound… or create a brand new one. Still, we humans are mighty crafty, and the people who brought us fire, the wheel and sliced bread have managed to design some pretty amazing ways to duplicate the process.
So where did it all begin? I’d like to think that, like fire, the wheel and sliced bread, early man created synthesis to fulfill a need. It could have been an audio aid in story-telling, the early “synth axe” being their mouth as they mimicked the snarl of the saber tooth, the whistle of a bird, or the moan of a dying mammoth. It also could’ve been a defensive or offensive tool — trying to reproduce the sounds a large predator makes could scare away a smaller one, or drive prey in the direction of a trap. Whatever the reason, man eventually found that he could make sounds with tools other than his own mouth — beating logs, strumming saber cat gut, blowing into antelope horns.
Civilization moved on. Hunters and Gatherers evolved into Farmers, and while the 8 hour work day and 5 day work week were still some ways off, there was more of what resembled free time to develop those early sound design tools into the precursors of modern instruments.
Fast forward a bit to the 3rd century B.C. It was a Thursday. A Greek engineer named Ktesibios decides to become the world’s first one-man band (history doesn’t record it, but rumor has it he’d been replaced by the girlfriend of the lead lyre plucker in his old band). He designed what amounted to a hand-cranked air pump, using water in a container to regulate the air pressure. Levers routed the pressurized air to different pipes, which tooted different notes. His “Hydraulos” not only made him the equivalent of an ancient Greek rock star, but also laid the ground work for modern pipe organs in the coming century — which were basically the first additive synthesizers, but I’m getting ahead of the story.
Next month, we’ll roll the Wayback Machine ahead to the 1400’s and the story of the Hurdy Gurdy Man, then travel forward in the journey to today’s sound-creating marvels. “When are we going to learn how to synthesize our own world of creative sounds” You ask? We’re getting there. Patience… after all, the world wasn’t created in one column.