I seem to recall reading about this running on minicomputers or mainframes, as described in another reply, and I also think this predated the Altair, as I first became smitten with computers around 1972.

Here's a video of a minicomputer generating AM radio music in 1971:

https://www.youtube.com/watch?v=akvSE5Z474c&lc=D5Mdy7u7Cxwsk...