I know that most pop/rock singles into the late 70's were recorded/engineered so it would sound good over AM radio, but a lot have been re-mastered later to sound good in the digital realm. But, I have yet to find a version of any of the early Chicago stuff (I'm a sucker for a horn section) like 25 or 6 to 4, or Saturday In The Park, that does not sound like it was recorded in a practice room on a cassette deck. I can't even hear the high hat on some of those. I've been looking for good versions, but the "remasters" that I found were no better than the originals. Other bands from that era, with horn sections, are nice and clean (Tower of Power, Motown, Blood Sweat and Tears, Memphis Horns, Van Morrison, etc).
Have they not been able to rescue the original tapes to remaster? It's irritating at best, and unlistenable at worst. Even the original vinyl through the best equipment I could find suffered that same issue.
In recording terms, it's like the horns oversaturated the tape, and while not really distorted, step all over just about everything else. Later Chicago songs did not suffer the same fate.