The alto flute is one of my favorite flutes. It definitely beats piccolo. It has a very mellow sound, sometimes almost woody, other times very ethereal. It’s especially fun to improvise on because all the percussive sounds are much louder than on my C flute. It turns out that Theobald Boehm (any flute player should recognize that name as the man who designed the modern flute) agrees with me. A lot of composers also thought fondly of it, or at least featured it in their music. The most obvious examples are in Ravel’s Daphnis and Chloe and Stravinksy’s Rite of Spring.
Rite of Spring: https://www.youtube.com/watch?v=VIjlXYQzO7w about a minute in is where the alto flute starts.
The alto flute is lower than the “standard” C flute by a fourth. It’s pitched in G, and its lowest note is G3, (the G below middle C). It does some things very well, such as expanding the dynamic range of the low end of the flute, but it has some limitations, such as the high register being a little weak and frequently thin or shrill. I like to think of it like the viola, the lower, mellower sibling of the violin/flute, with slightly different quirks.
Many flute players have a love/hate relationship with the alto flute (and bass flute and piccolo), mostly because we only practice them when we have a part that calls for it. This is similar to why new music with extended techniques is hard (see Multiphonics for that airing of grievances). I gotta say, there’s not anything quite like having a solo on an instrument you can’t quite play. I got called out by an orchestra conductor for not projecting on alto flute, (to my credit, it was mostly that I was playing a bad instrument) and subsequently spent several hours learning how to play it properly. So for everyone with access to an alto, play it! It’s fun, it’ll make your lungs and hands stronger, you’ll learn new things, be exposed to new music, and then when you get the question in orchestra, “who’s played alto flute before?” you will get that awesome solo ;)
Composers should also get to know the alto flute better. It can do almost everything that a C flute can do, and though it might sound different, (think about the differences between violin and viola), the percussive sounds, (key clicks, tongue stops, etc) are generally much louder and clearer.
For some inspiration check out these videos: