Driving here from another thread, some mention was made to the figure of Luigi Russolo, so here are some anchors for listening.
The “Intonarumori” created by Russolo is sort of a primordial analog synth, and the instruments leading the staves of his score “Il risveglio di una città” (1913) can be in effect regarded as just oscillators ante-litteram.
On the UbuWeb site:
one can listen to performances with Intonarumori sound generator replicas, played by a modern Intonarumori Orchestra from Japan.There you can also listen to the original works “Corale” and “Serenata”, remastered by the only 75rpm recording left of his performances.
I like to compare the work quoted above, “Il risveglio di una città”, with a 40 years - and two world wars’ - later work, “Ritratto di città” (1954) by Luciano Berio and Bruno Maderna, a radiophonic poem (here’s a reference link: https://youtu.be/CGCtmv_E5zE) where both electronic sounds, and concrete music techniques, were mixed and exploited in a mature way to build up a concep-art composition.