KeyFinder App to play along

Hi there,

I found a little app for iPhone (KeyFinder - free) that scans the music being played in the room and then shows in real time which key is being played. I like to kind of “play along” the songs I’m listening to, but by the time I sort of guess the key being played, well, the song is over!
So this little app is very useful to find the key right away. I have tested it with a bunch of classical music pieces and it seems accurate (classical music records/CD’s always shows the key being played (Sonata in Gb Minor, for exemple).

Once I see which key is being played I quickly run the scale on the bass to find the 3rd and the 5th. I then “improvise” on that triad.

My question is this; I see on the app the chord progressions in the first bars and then it only shows one key. I guess that key is called the dominant? So, can I keep on doing the triads in that dominant key for the whole song, even though I can hear the different progressions?
Perhaps @JoshFossgreen can enlighten me?

Also, does anybody use that kind of app, and if so, which one?


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Hey @Miguel_F, I’ve never tried that app, I have a hard time believing it really works without using it!

I don’t 100% understand your question, but I think I understand enough to say no, you can’t necessarily use the same scale the whole time just because you know the key. It depends on the chord progression a lot.

There’s no magic shortcut to knowing which scales you can use that works for all songs, without either training your ear really well to be able to analyze the music as good or better than an app can, or having reliable sheet music to work from.


My guess is that the app (if accurate) determines the chords played first and then use that information to determine the key it is in.
So at first it shows the chord progression it scans and once it’s sure of the key it switches to the key.

I haven’t used such an app because just like Josh I would have problems trusting it and also want to train my ears anyway but maybe there is some option so it shows the chord progression instead of the key? If you say it shows the chords correctly in the first bars it should be capable of it.

@JoshFossgreen Thanks for “putting the dots on the i’s” (French expression)
It’s much clearer now! I’ll try to find the sheet music for some of those songs I really like and see what they did (Yesterday I was trying to figure out “Superstition” by Stevie Wonder (great bass line there). Thanks again for your time.


Hi @juli0r , thanks for your feedback. You are right, the app does exactly that.
I tested it with pieces of music that I knew what key they were in (classical) and it was accurate. Maybe it isn’t good for all genres, specially if there are a lot of chord progressions.
It’s just that it’s very practical and immediate, and fun to play with like trying to guess which key it is by ear (and realizing how wrong my guess was).


I think this might be the closest discussion for my ask:

How can I find the chord progression of a song? In particular: “Bend it Blues”. Is there an app that can help me with this?

Its the first song here: Funky Jazz • Saxophone & Harmonica Blues • Slow Blues • 12 Bar Blues • Smooth Jazz Blues - YouTube

That progression on the bass starting at the :20 second mark is just so good. Seems like a slow, drawn out walk-up but definitely changing chords I think? I’ve heard versions of that in a lot of blues songs I love, but I don’t have the ear to figure it out myself. To be honest if I could learn to play this bass track on this song I could die a happy man. If you don’t get a little stank face listening to this you just don’t have any blues in your soul at all!

And while I’m asking for help. Is this blues song a G major pentatonic? Minor?

It’s not a normal 12 bar blues progression I think (too much other stuff going on?) I’m having trouble finding other versions of this to play around with.

So confession: a) I was kind of zoning out on some of Josh’s music theory, so maybe I should know this but missed it and B) My B2B progression has almost stalled, but not because I haven’t made progress. Just the opposite in fact. I’m just barely competent enough to jam along with blues backing tracks on YouTube, and I enjoy that so much that when I have time to pick up the bass I end up jamming instead of taking the next lesson or module. I’m not disappointed; I just wish I had time for both!.. and if I WAS progressing maybe I’d be able to do this myself, but here I am. :man_shrugging:


Oh wow; found another thread that led me to Chordify. Bend It Blues came right up. I think I might be able to make it work from here…