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I started learning piano not so long ago and there is something that's confusing me a lot: when I play some notes at the same time (chords or two notes) sometimes I hear a second higher vibrating sound besides the notes I play. It depends on which notes, for example I can hear it very clearly when I play G#3 and C4 in my digital piano. I've been researching and I suppose this might come from the overtones or maybe from the acoustic beats that they might produce.

I'm pretty sure this is not a problem with my keyboard since I hear this everywhere I play these two notes.

I uploaded a recording of these two notes being played together in some random website where I can clearly hear what I'm saying: https://on.soundcloud.com/rvJT6

So my question is: Is this normal? Does everyone hear this? I get very distracted by this while playing, could it be that they bother me more than to other people? When I play the Fm chord for example I hear this very loud

EDIT: I was just playing around with audacity and the same audio file that I shared and I found out that if I equalize it muting the 1000 Hz frequency I stop hearing the sound I mention, just and only that frequency (I suppose it's a range). If I make it louder I hear the thing louder of course and if I only play that frequency alone, then I still hear it.

So what I'm thinking is that this is a beat caused by the 4th harmonic of C4 (1046.502 Hz) and the 5th harmonic of G#3 (1038.262 Hz)

screenshot: https://imgur.com/MEsmVMA

2 Answers 2

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I don't know what you hear, but I can suggest some ideas.

Equal temperament is kind of out of tune, especially the thirds. The bottom note you're playing, G#3, which I would prefer to call Ab3, has a frequency of f_Ab3 = 207.65 Hz. Its fifth harmonic is a note a two octaves and a major third higher, that is C6, and its frequency is 5·f_Ab3 = 1038.25 Hz. Frequency of the note C4 is f_C4 = 261.63 Hz, and its fourth harmonic, also C6, has a frequency of 4·f_C4 = 1046.52 Hz. Difference between these two C6 is 8.27 Hz, which results in beating between these two harmonics, with a frequency of 8.27 Hz. This could be perceived as quick fluttering of the sound. This is the reason some people dislike equal temperament.

Edit: I just see your edited version of the post and it seems that the above guess is correct. Still, below I provide some other possible effects producing additional tones.

You may also hear a combination tone between the two notes, the most prominent one has the frequency equal to the difference between the two notes. In your case that would be f_C4 – f_Ab3 = 261.63 Hz – 207.65 Hz = 53.98 Hz. This is a note between Ab1 and A1, that is low pitch, and out of tune. But in order to hear it, you either need some kind of distortion (e.g. due to poor quality small speakers), or play it very loud (apparently ears can distort sound a bit too). But if played with moderate volume, on decent speakers, it shouldn't be the case. On the other hand, in an extreme scenario when large distortion is added e.g. with an electric guitar pedal effect, you would hear more harmonics and more combination/intermodulation toned between them.

There is some little hiss in the recording. I'm not sure if that's relevant for the question?

I recall with some older pianos you could hear quantization noise, in particular with very quiet notes, or at the end of the tails of decaying notes. This could be heard as a high frequency buzzing accompanying the note. I would hope recently made that instruments use enough bit depth for this not to happen.

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  • Thank you so much! I was amazed to see that what you mentioned first was what actually happend and I can fully understand it now. I'm still a little bit confused on why I get bothered by this but I suppose we don't all hear the same way. It also called my attention that you mentioned a hissing sound in the recording. Of course it was recorded with very low quality but I wonder if the hissing sound you mention is the actual sound I'm talking about which at least for me is very noticable mainly in the middle of the sound Jul 31, 2023 at 3:11
  • @user93987 There is some little hiss or noise in between the notes. Jul 31, 2023 at 3:14
  • The question mentions a digital piano. The synth could be emulating the tendency of a real piano to have 'stretched' harmonics due to the physical properties of the strings, which would impact on the frequency of the beating. Although I don't know what to make of "higher vibrating sound". Jul 31, 2023 at 10:41
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Overtones and Harmonics

Overtones are higher-sounding-tones (notes) that are produced when you play a tone (base frequency) on an acoustic or electric instrument. As you might already know, harmonics (or harmonic overtones) are a specific category of overtones, whose frequency is an integral multiple of the base frequency.

Harmonic vs non-harmonic sounds

A sound which predominantly features harmonic overtones is usually perceived as harmonic, which means that we can accurately gauge its pitch.

A sound that heavily features non-harmonic overtones is usually perceived as the opposite; you'll have some difficulty discerning the pitch.

When I first learned of this in an acoustics course, I was immediately reminded of the church bells in my hometown. I was always having trouble figuring out their melodies.

Consonance and Dissonance

Now as to how these relate to your question. Base frequency and overtones both have everything to do with consonance and dissonance. The more two sounds' overtones overlap, the more consonant we perceive them to be. That's why the octave is the most consonant interval: the notes share all of their overtones.

Hearing overtones is completely normal

While not everyone finds it easy to spot overtones, under certain conditions they can be quite audible. I was tuning a spinet in my school, and playing the octave interval of E - e produced a very audible overtone of a B, which (expressed as a simple interval) is a fifth.

Are you hearing overtones or beats?

I am not very acoustics-savvy, but my understanding is that the beats you are hearing are the result of some of the overtones of your interval (I'd call it Ab - C, a Major third) are not matching up exactly. In a way, if you're hearing beats, you're hearing overtones too. Whether you can discern both of the overtones, which probably are only a few cents apart, is another matter entirely.

tl;dr Hearing overtones is normal, although sometimes a bit challenging. Overtones are easier to discern when they are harmonic, especially when boosted by a resonant harmonic sound (e.g. an octave below).


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