An analog synth is an instrument where the circuits generate and process sound along a continuous signal path. In a basic case, an oscillator produces a simple waveform which is sent through a filter before the sound is amplified and sent out through the speakers.
“I love the idea of messing with frequencies that are already alive. It's an amazing concept.”
Emily Kokal of Warpaint likes to build sounds that don’t poke out as hyper-electronic, and finds analog synthesizers are great for that.
An analog oscillator typically produces a periodic signal, a simple, regular waveform. If a sine wave is all you send to an amp, you’ve got a tone generator. Great, if you’re doing a hearing test. For music, perhaps not. Other simple waveforms, like saw, square and triangle, give you a few more options.
Oscillators used in analog synthesizers do not produce geometrically perfect waveforms like the ones seen in the illustration: in fact the source of the distinctive, unique sound of a synthesizer is defined by how its oscillators render the simple waveforms. Try clicking on a waveform below to hear it.
Filter and Overtones
As you can hear, even with a few basic shapes to choose from, sending any of them straight to the amp does subtle musical difference. This is where the filter comes into play. If we send a pure sine wave through, nothing happens to its timbre. Timbre is the characteristic spectrum of overtones (harmonics) of a sound.
If we send a non-sine waveform through the filter, its overtones are reduced or emphasized at the cut-off frequency, changing the timbre of the sound. With a resonant filter you can really add life and excitement to the sound. Now, we can make music, right?
“There’s life in the analog. There are all the little imperfections, all the non-linear stuff that happens to us every day in life.”
Rik Simpson, Coldplay producer, uses any great musical tool; old or new, digital or analog. He muses on what makes each of the technologies special in its own way.
Not so fast. We’ve made the signal cool, rich and timbral, but we want to decide how it’s played back through the internal amp, too. Do we want it to blast forth at its maximum level when we hit a note, and vanish instantly as soon as it is released? Perhaps not. Modulating the amp with an ADSR envelope, we can alter the phasing in of the signal when we hit the note (Attack), the phasing out (Decay) toward the amplitude level while keeping the note on (Sustain), and the final phasing out of the signal when we (Release) the note.
Want a quick stab sound or a slowly rising and falling one? A stab top and a slow tail, or the other way around? Just rock the ADSR envelope.
All Together Now
Forget all the above. We’ve seen the building blocks, but looking at them one by one misses the whole point of the truly wonderful: tweaking all of it. If we add another oscillator, we can really stir things up. In the simplest case, if both have the same frequency and phase (crests and troughs line up perfectly), we get a resultant that is identical but with greater amplitude, a stronger signal. If the two are identical but of opposite phase (crest over trough, trough over crest), we get an almost silent resultant signal.
Mixing two different waveforms produces a complex signal, with a potentially musical timbre. Letting an LFO (Low Frequency Oscillator) set to a frequency below the audio range modulate the amplitude of the signal results in a wobble. Modulating the pulse width adds another type of movement to the sound.
There are so many combinations to explore! The beauty of an analog signal path is how well it connects to the physical world, the world of the senses. We can touch it, feel it and twist it until we hit the spot.