Synth Education

The Hybrid Voice (LA Synthesis)

Real instruments have complex, noisy attacks that synth oscillators simply cannot fake. But splice 200ms of a real attack recording onto a synth sustain and your ear is completely fooled.

Sample Meets Synthesis

Roland figured this out in 1987 with the D-50. The trick is called Linear Arithmetic (LA) synthesis: use a short sample for the attack transient, then hand off to a traditional oscillator for the sustain. Your ear judges "what instrument is this?" almost entirely from the first few hundred milliseconds. Get the attack right and the sustain can be a plain sawtooth -- your brain fills in the rest.

Below you can hear the difference. In "Synth Only" mode you get a raw oscillator with a filter envelope. It sounds like a synth. Toggle to "Hybrid" and the same sustain now starts with a realistic attack sample. Suddenly it sounds convincing.

Why This Works

Psychoacoustics research shows that humans identify instruments mainly by their attack transients. A piano hammer hitting a string, breath noise as a flute note starts, the snap of a guitar pick -- these micro-events are what your brain keys on. The sustained part of the sound is harmonically simple by comparison. So a short sample of the attack, crossfaded into a synth oscillator for the sustain, is enough to fool the ear.

The crossfade point is the seam. Too early and the synth character bleeds into the attack. Too late and you are wasting sample memory on sustain that an oscillator can handle. The sweet spot depends on the instrument: piano hammers settle in about 200ms, flute breath takes 300ms, a guitar pick is done in 100ms.

What the Controls Do

A/B Toggle switches between "Synth Only" (just the oscillator with a filter envelope) and "Hybrid" mode (attack sample spliced onto the synth sustain). This is the main interaction -- hear the difference with one click.

Attack Source selects which kind of transient starts the note: a piano hammer impact, breathy flute onset, sharp guitar pick, or slow bowed string attack.

Sustain Waveform sets the oscillator type for the sustained portion of the note. Sawtooth is the most versatile, square adds hollowness, triangle is softer.

Crossfade controls where the sample ends and the synth begins, from 50ms to 500ms. The "Reveal Splice" button shows the exact splice point as a vertical line on the waveform scope.

References

• Wikipedia: Linear Arithmetic synthesis
• Roland D-50 (1987) -- the instrument that popularized LA synthesis