Synthesizer music

No musical instrument, other than a synth set up appropriately, generates a pure 1khz sine wave. They all have a natural harmonic series (of, usually, even harmonics!) and the composition of that harmonic series determines the nature of the tone (the timbre) of the instrument. Synths, including virtually all forms of the organ, deliberately bring the manipulation of the composition of that harmonic series within the control of the performer, and so allow them to synthesize different sounds. It's fully intended, so not distortion :-)

If, OTOH, the amp does this all by itself in response to a 1khz sine wave, then that definitely is distortion. And this is why some groups of listeners like certain types of amplifier, because the "right" kind of distortion adds harmonic interest to the sound. It's the "right" kind of distortion because it follows the natural harmonic series that we're all familiar with just from hearing natural sounds.

My father had lots of synth music including JMJ, Tangerine Dream, and Rick Wakeman. In the new wave era I enjoyed the early Human League albums, Ultravox, Gary Numan, and John Foxx among others. The Peter Gabriel albums have a lot of syntheised and sampled sounds. Fortunately I still have all the LP's from these artists and things like Vangelis too. I'd also add Who's Next as a good example. My sense then and now is that a lot of hard work went into creating those sounds with relatively simple analogue equipment. Whilst loving that cutting edge I'd agree with RichW abou the sophistication of modern synth music.

Not a synth but the enrichment of amplifier distortion made me think of Jon Lord's Hammond through a Marshall amp, yielding 'the beast' you'll hear on classic Deep Purple albums.