Elektron Interview with John Chowning, the Father of FM Synthesis & How to Explain FM to a Child

Elektron recently announced the Digitone Digital FM Synthesizer. They've posted an interview with the creator of FM synthesis, John Chowning, on Elektronauts here. The following is the beginning excerpt including how John would explain FM synthesis to a child, meaning anyone new to FM synthesis.  :)  Note when he mentions vibrato depth increasing he is referring to one operator or oscillator modulating another.  In FM synthesis you have different mappings of operators modulation each other.  Be sure to see the full interview for more, including other topics.

"We had a good, solid talk with John Chowning, inventor of FM synthesis. Since its first musical use, FM has greatly expanded the musical possibilities of digital instruments. Its impact on every imaginable genre cannot be overstated, from contemporary classical music to dubstep. It was the synth sound of the 1980s, immortalized through the Yamaha DX7. John, however, does not refer to it as an invention. According to him, FM is a gift of nature that was just waiting to be discovered.

Now, understanding FM may seem daunting at first, as it incorporates some fundamental properties of math, music and acoustics. The beauty of John’s discovery is that (once properly used in a synthesizer) you don’t need to fully understand it. Just use your hands and ears to intuitively produce musical results that are pleasing, surprising, harmonic or inharmonic to your heart’s desire.

How would you explain FM synthesis to a child?

I would show the child how he or she might begin clapping two hands together, faster and faster and faster, them jump to the computer and show that we can make the claps even faster than the child is able to clap, and have the child listen to what happens. How the rate of claps changes from once per second, gradually through 8 times per second, to 16 times per second, all continuously increasing the rate until the child begins to hear a pitch.

At some point, I would say: 'why don’t you hum the pitch that you hear?' Now, I would do the same thing in reverse, you hear the pitch which the child has hummed, maybe something like 400 Hertz, which would be pretty close to G above middle C. Then I would reverse it, and as it slows, ask them to jump at in the moment they think they can clap that fast, and then slow down the computer-produced clap. We’ve established the fact, that when things happen at a certain rate, about 20-30 times per second, you no longer hear things as individual claps. You begin to hear things as tone quality (timbre) and then pitch.

Then I would do the same thing using the computer, with a sinusoid changing pitch — a vibrato. With a violin at hand, I would show what vibrato is — at the same pitch that the child hummed — and let my finger go up and down the fingerboard at an increasing rate. Again, jump to the computer with a sine wave at the hum pitch of 400Hz, with a vibrato depth increasing to ±40Hz at a rate of 1Hz. Then gradually increase the vibrato rate from 1Hz to 400Hz. As a last step I would gradually increase the vibrato depth to ±400Hz and we have caused the quality of the tone at 400Hz to change. All of a sudden we hear frequency modulation synthesis as a model of the original violin. That’s one way of explaining it!

It’s a phenomenon that has to do with the auditory system, and I think it’s partially understood why it happens. It can be intuitively understood when we connect it to a real-life case, like vibrato in a musical instrument, which is a special case of frequency modulation. Once we’ve got the sinusoid modulating the carrier from 1 -400 Hertz, then we can change the distance up and down the keyboard, and show how the quality of the tone changes with deviation. That’s basically how I would explain the properties of modulation rate and modulation depth to a child.

(I would also change the order in the demonstration, which is equally, if not more interesting — that is, first increasing the deviation of the 400 Hz sinusoid from ±0Hz to ±400Hz at a rate of 1Hz and then gradually increasing the rate from 1Hz to 400Hz.)"