Why do “in tune” bass lines sometimes seem sharp to me?

Question

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.

Answer 1

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

Answer 2

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.)

Answer 3

[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?

Answer 4

For what it's worth, the headphones or speakers you're using can change a lot of these characteristics.

I remember when the foam padding on my headphones wore off and I replaced them with padding made by a third-party manufacturer which was too thick. Low frequencies leak out a lot due to the distance between the speaker and ear, amounting to an inherent treble-boost which I usually fix with a treble reducer equalizer setting.

My experience so far (somewhat subjective) is that treble and midrange hold better over a long range, while low frequencies (with sufficient amplitude) are better at going through walls (you can confirm this by standing outside an overly noisy club with speakers belting out boosted EDM basslines).