How to jam alongside existing music and you're not playing the guitar
It's long been my goal to play with music—to riff on it, expand or embellish or change or add stuff to songs I like. There's like 1.518e7 youtube videos about jamming with a guitar, and basically nothing with flutes, so I'm having to figure out stuff by myself. I'm not skilled at any of this so take it with grains of salt, but:
There's a saying, “the wrong note on rhythm is jazz; the right note with the wrong rhythm is noise”. Rhythm makes the difference between boring arpeggio exercises clashing with the music, and music; much more than any complex harmonic theories. Pay attention to the drums and percussion. Tune in with the rhythm with your whole body and keep that in your bones, that will put you in sync with the music.
Easy mode: Backing tracks. The type that shows the chords on screen is ideal: look up the notes on each chord, and a pentatonic or other improvisation-friendly scale to play on that key. (For the miyakobushi scale, “Phrygian” backing tracks work well.) First play only the root note of each chord; then try arpeggios or a few free notes of each chord as they come, in rhythm. Don't get overwhelmed trying to hit all of them, one or two notes are fine – instead, focus on staying musical from the get-go. Then experiment with the rest of the scale. Don't be afraid to break the rules and play passing notes fully outside what you're supposed to play, oftentimes they sound sick.
The purpose of all the harmony rules and stuff is to describe which notes sound good together. More important than that is to develop your sense of what notes sound good together. If you think they sounded good, then they did, you're making music that you like. I find the theory useful because if I just play random notes with no restrictions whatsoever it doesn't sound like “music” and I don't like it, and the theory gives me a starting pack of things that are easy to make work. But don't let the theory and the rules distract you from the need to exercise your own musical sensibility, to pay attention and tune your ear.
When you find a thing that worked, milk it. Repeat that little successful riff a few times.
Sometimes your intuition will want your fingers to do something with lightning-fast speed, and you have no idea why. It comes from some instinctive, sub-rational place. That place is the fountain of music; give your fingers to it.
When playing with finished music, the bass is your cheatcode. In the large majority of cases the bass of each measure is informing you of the root note of the chord, right at the first note. The rest of the bass riff gives you a little bag of notes that are guaranteed to work on that passage. It's much easier to pinpoint the bass notes than trying to reverse-engineer chords from harmonies. A bass tab gives you a map of stuff you can use to jam safely, and from there you can experiment. Moreover, the bass is lowkey percussion; paying attention to bass will automatically put you in the rhythmic vibe of that song.
Do like the bass and become percussion. E.g. pick a single note and go like “tuh-tuh-tuh” or dunno “tuuh, tuh-tuh / tuuh, tuh-tuh”, or whatever fits that song. Instead of trying to add melodies, add to the rhythm of the music.
On a similar note: drones. Instead of adding melodies, become atmosphere. My wind instruments like the flute, the xūn and the melodica work great for this. Swell in and out of long notes on the back, like a backing vocal going “aaahhh…”, and find out how that harmonises with the passage, or doesn't. Often a single note will be common to many chords and therefore work for very large passages (someone pointed me that almost all chords of “Hey Jude” have a C note, and the ones that don't have a D note, so you can “aaaahhh...” through the entire song by singing a C and changing to D when you feel like it doesn't fits; it works and it's very fun).
A good example of this is Otonoha's shinobue adaptation of Cosmo Canyon – not the more obvious main flute melody, but notice the “backing flute” layers playing long notes in the background.Call-response. Instead of trying to play alongside a singer or lead guitar, let them draw a melody, then try to repeat it on the flute an octave higher, or repeat it but change it a bit. Listen to jazz jamming to get a sense for how they do it.
Counterpoint! I mean I can't do counterpoint on the fly with my flute lol but at a super simple level: when the singer is going up, try playing along but going down instead. See what happens.
I have to take my own advice on this: just do the thing from the get-go. Since I want to play with existing songs, to embellish or change or add to them, try it. Yeah it doesn't sound very good but doing it regularly starts sinking in some skills. Just be sure to stay deliberate—pay attention to what worked and what didn't; experiment and keep what works.