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.

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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).

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