Building Sounds From Scratch: How Synthesizers Create Music

In 1964, engineer Robert Moog built one of the first practical synthesizers out of circuit boards, patch cables, and knobs. With the right settings, that same box could growl like a bass, whistle like a flute, or buzz like an alarm. No microphone, no recording of a real instrument — every sound was built from raw electricity. That is still how synthesizers work today, just with software instead of cables.

- How oscillators generate the raw waveform a synthesizer starts with - How filters remove frequencies to change the tone of a sound - How an ADSR envelope shapes volume over time - How engineers combine these three tools to design a specific sound

Every synthesized sound starts with an oscillator, a circuit or piece of code that produces a repeating waveform. The four basic waveforms are the sine wave (a smooth, pure tone with no extra harmonics), the sawtooth wave (bright and buzzy, common in synth basses), the square wave (hollow and reedy, used for classic video game sounds), and the triangle wave (soft, similar to a sine wave but slightly brighter). Each shape contains a different mix of harmonics, which is why a sawtooth wave sounds harsh while a sine wave sounds smooth even at the exact same pitch.

A raw oscillator wave is usually too harsh to use by itself, so it passes through a filter. A low-pass filter lets frequencies below a chosen cutoff point pass through and reduces everything above it, making a sound darker and smoother. A high-pass filter does the opposite, cutting the low frequencies and leaving a thinner, brighter sound. Engineers set the cutoff frequency, often somewhere between 200 Hz and 5,000 Hz, and adjust resonance to boost the frequencies right at that cutoff point for an extra sharp, whistling edge.

A single held note is not the same volume the whole time it plays — a piano key struck hard starts loud and fades, while a violin note can start soft and swell. Synthesizers recreate this with an ADSR envelope: Attack (how fast the sound reaches full volume, maybe 5 milliseconds for a sharp pluck or 2 full seconds for a slow swell), Decay (how fast it drops to a middle level), Sustain (the steady volume held while a key stays down), and Release (how long the sound takes to fade out after the key is lifted). Changing these four numbers is often the single biggest reason two synth patches sound completely different.