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I've noticed that certain bass and baritone register sounds often seem sharp to me, even when they are ostensibly in tune- the notes are checked with a tuner or generated by a digital synth that won't go out of tune. I've also noticed that some sounds seem to go even sharper at high volumes. What is causing this discrepancy between perceived pitch and the "actual" pitch of the instrument?

I've read unsourced claims that at high volumes, high frequencies sound sharper and low frequencies sound flatter. I haven't found good reputable or detailed sources for this.

I was reminded of this phenomenon by this question.

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  • Is it more noticable with some instruments than others? Say a bass guitar frequently sounds sharp, a piano less so, vocals very rarely? I think the answer is 'inharmonicity', but it affects different instruments differently. – j-g-faustus Mar 17 at 17:28
  • I totally expect inharmonicity is one reason why an instrument may sound sharp. You could expand that into an answer. I don't think it's the only factor though. I noticed the "high volume => seems sharp" effect the most with a certain saw-like synth from the garageband app, which is probably not inharmonic. I may be able to find/provide a sample, but I don't have an iPad anymore. I've also noticed perception errors with sine basses when I first got bassy headphones years ago, but I think I'm just used to them now and no longer hear them as being out. – Edward Mar 17 at 18:26
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You are right about loud bass notes sounding different to what they are. Whenever I tuned the bottom E by ear prior to a gig (off the 3 treble strings ADG) I would check it by tuner with disappointment that 'my ear was deficient'. What the tuner says is correct pitch (41.2 Hz) always sounded sharp to me, and what my ear said was in tune the technology says is flat. I think it has something to do with sound pressure and the effect on the human ear drum - and partials creating inharmonicity. On a piano the bass notes are tuned flatter and the treble notes sharper - stretching the octaves aka the Railsback Curve

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It may be that your perception is "correcting" the equal temperament physical pitch to something that makes more sense to your brain, e.g. just intonation where the ratios between the pitches are more in line with the actual overtones present.

("more in line" because of inharmonicity.)

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[This would probably better fit as a comment as I do not have any references to support it, like you I am looking forward for other answers…]

All these bass sounds are not pure sine tones thus, they will generate harmonics according to the harmonic series: the first one will at the octave, the second one at the octave plus a fifth plus roughly 2 cents compared to 12TET. Usually the volumes of these harmonics will be lower than the fundamental tone.

That said, the human ear is more sensible to mid range sound than to bass sounds. That means that the perception of the harmonics will be boosted compared to the fundamental tone as these harmonics are at higher frequencies. The second harmonic, which is a bit sharper than the fifth obtained from equal temperament will thus be boosted compared to the fundamental for bass sounds. Maybe that is what is driving this perception phenomenon?

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  • I'm quite confident that the second harmonic, at only 2 cents sharp, is not contributing much to this perception error of much more than 2 cents. If you look at the first, say, 20 harmonics, then you might have something, but the first 20 harmonics seem overall to be flat compared to 12-TET more than they are sharp. – Edward Mar 17 at 12:48
  • @Edward Honestly, I was never very good in tuning so I trust you on that. As said that read more am hypothesis than a real answer! – Tom Mar 17 at 13:09

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