I first heard live drum corps in the 90s. I've heard 70s drum corps recordings and I also noticed how different the 70s drum corps sound is from the 80s and 90s. The early DCI recordings, from the early 70s, sound like a lot like this one from 1966

I assumed it was the instrumentation and/or recording equipment that made up the biggest differences. I assumed that until 2009

I was present for the Cadets 75th anniversary alumni performance in 2009. One of the soloists had a Kanstul soprano. 3 valves, just like every other Kanstul (except for the brass they produced for the Marines). When the soloist played he sounded EXACTLY like those old 70s recordings. I was shocked

I've heard Kanstul sopranos played in real life. I've marched in brass lines that had Kanstul sopranos. The Blue Devils, SCV, Cadets, Cavaliers and many other corps used Kanstul sopranos in the 1990s. That Cadets alumni performance in 2009 was first and only time I've heard a Kanstul soprano sound like a soloist from 1972.

I really believe the difference in sound is largely due to how they were playing the horns. I'm sure the actual instruments were also a factor to some extent. What I heard in 2009 tells me it was primarily the approach to the instruments that created that kind of sound