I recently purchased a NUX NPK-10 electric piano, as a step up from a Yamaha keyboard. I love the instrument, and I'm enjoying playing it. However I have noticed a bizarre effect that I cannot explain.

When I strike g5 and d5 simultaneously and hold them, a noticeable and almost obtrusive overtone sounds, an octave up from the g, and sustains as long as I hold the two notes. The effect is also noticeable, though less pronounced, with the fourths ranging from c5/f5 to e5/a5, and absent above and below that range. I don't get this effect on other intervals in that range.

It's not a discordant tone, but it's unexpected and a little distracting, sounds almost like something in the room is resonating with the piano, or within it. At first, I suspected sympathetic resonance from one of my other instruments, or else a loose screw near the piano's speaker.

However, I find that when I strike the same notes while holding down the damper pedal, I do not get the overtone, which suggests that this is not a physical resonance issue at all, and now I suspect that this is a software issue, specifically, this is how this instrument models the sound of those notes played together, in "grand piano" mode, without the damper.

Can anyone help me understand what's going on here? For example, is this a known issue with this particular keyboard? Do other electric pianos have similar issues? Is there any way to correct this? If this is the only problem with the instrument, I can deal with it, but it would be nice to not have that bonus note :)

  • 3
    Recently purchased? Sounds like back to the seller to me.
    – Tim
    Commented Sep 22, 2022 at 15:45
  • @Tim I can understand the impulse behind your suggestion, but if I'm correct in thinking that this is a software issue with this instrument then I'd expect any replacement to have the same issue. In that case, I'd rather work around this issue as the instrument is overall the best one I've found in this price range for my purposes. Commented Sep 22, 2022 at 16:40
  • 1
    I understand the idea is that the replacement wouldn’t be a Nux. I haven’t heard anything good about the brand but this sounds really bad.
    – ojs
    Commented Sep 22, 2022 at 18:21
  • 2
    @JonKiparsky to me the description sounds more like it's a terrible waste of money at any price. At that budget I'd look for a second hand stage piano from Yamaha, Roland, Kawai or maybe Casio.
    – ojs
    Commented Sep 22, 2022 at 20:19
  • 6
    Perhaps you can distinguish between software and hardware issues by recording the audio output from it? (And if you post the results here, that could be useful extra info.)
    – gidds
    Commented Sep 23, 2022 at 0:44


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