You’ve seen the filter settings on your synth, maybe you’ve tried changing the settings and can hear the difference, but what is going on? What is a filter anyway? Well, the filter on a synthesizer is just like any other kind of filter. An air filter in your car, a water-purifying filter, a spam filter, they all do one thing: remove stuff. So what stuff does a synthesizer’s filter remove? Frequencies.
In a previous episode of the podcast we looked at the oscillators that produce frequency-rich tones. But what happens when you have too many frequencies present in your sound? Well, that’s just noise. In fact, that’s the definition of white noise: all frequencies present at equal volumes. Our filter lets us remove frequencies until what’s left is something you can use in your music.
The most common filter on synthesizers is the Low Pass Filter or LPF. Listen to the episode to hear how the LPF shapes your sound. (spoiler alert: it removes high frequency content and leaves you with low frequencies.)
Here’s another one of those acronyms you’ve seen on your synth. An LFO is a Low Frequency Oscillator. Since the last episode covered oscillators, you already know that an oscillator generates sounds. Well, the LFO is different in that its frequency is generally so low that you can’t hear it. Instead the waveform is applied to modify something else in your sound.
Common LFO modulation approaches include changing the frequency cutoff, the pitch of the tone, volume, etc. Most synths offer a wide range of things you can modulate with your LFO. And, many offer several LFOs that operate independently of each other. Listen to the episode to hear what LFO modulation sounds like in action.
To learn more about filters and LFOs, check out this book at Amazon.com: The Synthesizer: A Comprehensive Guide to Understanding, Programming, Playing, and Recording the Ultimate Electronic Music Instrument.