Every form of saturation is a shape — a curve that maps input to output. Feed a clean sine wave through that curve, and the shape of the curve determines which harmonics appear, how the waveform deforms, and whether the result sounds warm, gritty, buzzy, or broken. The entire character of a distortion comes down to one question: what does the curve look like at the edges?
Dashed line = output equals input.
Colored curve = what the circuit does.
Key insight: Even-order harmonics are musically consonant — the 2nd harmonic is an octave above, the 4th is two octaves. This is why tube saturation sounds 'warm' rather than 'harsh.'
Generated by asymmetric clipping — when the positive and negative halves of the waveform are treated differently. Musical intervals: octaves, major thirds. Sounds warm, full, “musical.” Sources: tubes, tape (slightly).
Generated by symmetric clipping — when both halves of the waveform are treated identically. Musical intervals: fifths, minor sevenths, ninths. Sounds edgier, grittier, more aggressive. Sources: transformers, transistors, digital.
Every piece of audio equipment saturates. Tubes, tape, transformers, transistors, digital converters — they all have a ceiling, and they all do something different when the signal hits it. For most of recording history, this wasn’t a feature. It was a limitation engineers fought against, carefully managing levels to stay in the linear range where the signal passed through unaltered.
But the clean signal was never quite as interesting as the pushed one. Guitarists discovered this first — that an overdriven amp had a voice that a clean one didn’t. Then producers discovered it on their consoles and tape machines. Then mixers started deliberately printing drums and vocals hot to tape, chasing that compression and warmth.
What they were all discovering, in different ways, is that saturation adds information. A clean signal is just itself. A saturated signal contains new frequencies that weren’t in the original — harmonics generated by the nonlinearity. The circuit is composing, adding notes the player never played. The transfer curve is the score.