A simple explanation would be something like this in D major.
The 1/16th note run is just my interpretation. It could also be in G major, but D major feels like a simpler answer.
Here's what it could sound like
Chords in that Vocaroo clip that has the lick twice in a row
| Em7 A7 | C#7#9 F#7 Bm Am | G Em7 | A7 Eb9 D |
... what happened, the chords automagically turned into guitar chord diagrams?
I'll make it a picture instead
Here's how it could sound in G. At first I thought this was too far-fetched, but after listening to it a few times it starts to sound OK.
| C Bm7 | Am7 D7 G | Am7 D7 | Am D7 G |
If you just spreat the phrases differently, the line can be anything. Here's a pop song chorus in B minor.
A similar chord progression is used in any number of existing songs.
| Em A | D G | Em6/C# F#7 | Am6/F# B7 |
The way I make chord progressions for "audio melodies" that aren't written down as music notation goes something like this:
- First I try to imagine a beat and meter on top of the notes, because where "one" is and where the pulse is, decides which notes feel stronger harmony-wise. (it's important that you have only a single-note melody without chords, so if there are chords, re-do the melody without them)
- Then I get an idea of what keys it could possibly be in, based on what notes are emphasized and what sounds like a strong note, what the scale feels like. Here the obvious choices are D major / B minor or G major / E minor.
- I listen to and play the melody on top of my beat, and it usually speaks for itself, outlining some chords. For example the notes B - G played on the strong beat are a very strong indication that the most natural choice for chord is G major or E minor, and any other choice is more "creative", (since we decided that the key feels like D major or G major). For example an A9 or G/A would be a nice chord choice. Cmaj7 would work if the key is G major, but if the key is D major then Cmaj7 is a "creative" choice. G7/F might be interesting, but it's more on the creative side as well, with the outside-scale F note, needing a bit of modulation trickery.
- I decide on some starting and ending chords, and then fill the space in between them with something.
- The "something" is done with swings and turnarounds of the harmony, often using voice leading to give inspiration. Basically, everything is just I, IV or V of some key, either on the major side (D, G, A) or minor side (Bm, Em, F#m or F#). Voice leading could be like, take a bass note or some other note and start moving it step-by-step. Either (1) steps along the scale, (2) steps along the circle of fourths/fifths, or (3) steps along the chord tones. And then use a chord that fits that new stepped voice.
- Then re-do the whole thing a few times over. Try to think of alternative ways. If possible, change the start and end points and the middle points, make the turns go the other way: IV, V, I or IV, I, V or whatever. If a voice stepped downwards, step it upwards. As long as it feels appropriate and/or interesting. If it's too boring and obvious, try adding some non-obvious things like modulations, "chromatic mediants" (a new word I learned from the interwebz), secondary dominants, tritone substitutions, pedal tones.
- (Actually, usually I cut corners and do the whole thing on the fly, trying to accompany the melody right away as it's playing, but I guess that wouldn't serve as a sensible process description)
Very often, you can fit an existing known chord progression on the melody. If you play a lot of songs by ear, at some point chord choices start to offer themselves pretty much automatically.