Why is it that when I play a major chord on my guitar, the tuner shows the correct chord, even if the root isn't in the bass ?

  • 1
    How many different voicing have you tried? Tuners aren't meant to handle more than one note at a time so it's most likely a coincidence for whatever shape you are using as a result of it. I'd be really impressed with a tuner that can always identify a root note as even cutting edge DSP can't grantee finding the root note based on the resulting signal alone yet.
    – Dom
    Commented Dec 15, 2015 at 21:09
  • 2
    Not exactly Dom, my PolyTune can tune all the strings at once.
    – mike628
    Commented Dec 15, 2015 at 21:12
  • After looking at the specs, you are right that it can tune all the strings at once, but it doesn't display a chord only 1 note which can look like a chord symbol if it is a major chord because a major chord's symbol is typically just the root note, but isn't the same thing. And still ditto my last sentence from a previous comment.
    – Dom
    Commented Dec 15, 2015 at 21:18
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    Thanks Dom, I didn't think it was showing the chord, but why does it "Seem" to know the root. Can this have anything to do with harmonics ?
    – mike628
    Commented Dec 15, 2015 at 21:25
  • Theoretically yes, but it's not that simple of a task as while you could see what the strongest frequencies are in the signal, correlate them to notes and weight them, and then based on the set of notes and their rankings determine what triad best correlates to the notes while still dealing with noise. It's a lot for a little tuner to do and I guarantee it's not perfect. What is most likely happening is the way the method the tuner uses to display the giving note goes to the root coincidentally for the voicing you are using.
    – Dom
    Commented Dec 15, 2015 at 21:59

1 Answer 1


Depending on how your tuner detects frequency, it's possible that this is because of the resultant tone phenomenon.

If we play two sinewaves, one at 100 Hz (about G2), and another a musical fifth above at 150Hz, and then add the waveforms together, the summed result is a waveform whose actual frequency is the difference between those frequencies - ie. 50 Hz (about G1).

If we play a note at 100 Hz and another note 25Hz above, which is a Major third above, the resultant tone is at 25Hz - around G0.

This will even work with some inversions. If we play 150Hz and a G an octave higher - a (slightly flat) G3 at 200 Hz, the resultant tone is still 50Hz and still a G.

I don't think this would explain it if your tuner can ALWAYS pick out the right chord - especially as real notes aren't sinewaves, so it won't work as simply as I outlined - but it may explain why some voicings 'work'.

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