Alto Trombone

For a while now, I have been outplaying my starter trombone. My teacher tells me that I need to get an upgrade, so I've been looking for a good model. I currently have a tenor trombone, and thought about getting one with a different voice range. A bass trombone seems like a good consideration, but I really love the sound of the alto trombone. It reminds me of a French horn, but it really doesn't sound too much like one. There's really not another instrument I can compare it to. The alto trombone isn't that popular nowadays, but it was a well-known instrument back in the 1600s and 1700s. Unfortunately, this instrument seems like it would take a good while for me to adjust to. I can play a lot of notes in its range, but I would probably have to re-learn the note positions, and have to learn all of my music in the tenor clef instead of the bass clef. Plus, I don't know if there's a lot of concert/marching music I could play with it in band. So, for now, I may just stick to a tenor or bass trombone, and wait to learn to play the alto trombone, even though it is such a beautiful-sounding instrument.