If they survive at all, recordings of a lot of older music (pre-50s or -60s) don't sound great because they were taken from old records that aren't in the best shape. This 1929 recording of Louis Armstrong & His Orchestra playing Ain't Misbehavin' was taken from what's called a "mother record", a metal disc that's produced from the master disc. As you can hear, recording directly from a mother gives you an incredibly crisp and clear result:
Wow. It sounds so much better than the same song recorded in a more conventional way:
We're so conditioned to hearing 90-year-old music with that muddy record hiss that the mother recording is a revelation, like seeing early color photography and film.