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I notice that on bass guitars or low tuned guitars, the notes played on the lowest strings very high on the fretboard sound bad. This can be heard, e.g., in this video at 1:01–1:10:

It is well known that notes higher on the fretboard, and on thicker sound more mellow as they produce less harmonics. However, on the lowest bass string I can hear something else, as if the note was out of tune with itself. I fail to find a better description for it, and I hope the audio example clarifies it.

  1. What properties of the sound make it appear this way?

  2. What is the reason, and what can be reasonably done to reduce this effect (besides avoiding that area of the fretboard), e.g., by choosing string gauge, material, scale length, etc...

After writing all this down, I realize... is the reason inharmonicity of the overtones? But if so, what is the source of it?

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    You've chosen a really poor example. Try it on a real bass. That one's as sharp as all hell that far up the neck on the bottom B. They even fade it out early so you've less time to notice. Either someone got the intonation wrong, or forgot to check the tuning… & they released it with that error. Someone wasn't paying attention.
    – Tetsujin
    Commented Nov 2, 2023 at 17:11
  • @Tetsujin I am not sure about it. I feel like the note is out of tune with its own self. If the reason is indeed inharmonicity, then it might be that the fundamental frequency (which they presumably used to adjust the intonation) is in tune, while the harmonics are off. Then, the ear may pick one or another more. Anyway, intonation is something I can adjust, but it doesn't fix the issue of the note sounding bad on its own. Commented Nov 2, 2023 at 23:44
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    Melodyne broadly agrees with my ears. This is the last 8 notes, 4 in tune, 4 out - i.sstatic.net/jaieC.jpg - the B string glisses down, but never quite gets there. The 4th note is absolutely nowhere near. The string is dull & thuddy, which is exactly what you'd expect if your were dozy enough to play right up there;) The gliss might be a side effect of that - it would certainly make me look at strategy; strings, intonation, playing style etc. My bass only has 20 frets & I don't think I've ever gone above 15 on the E. It doesn't have a lot of practical use, right up there.
    – Tetsujin
    Commented Nov 3, 2023 at 8:26
  • I agree with Tetsujin, it can also come from a poorly tuned bridge, where the instrument get more and more out of tune the higher you go on the neck. Bassists tend to be less precise about this tuning as they rarely go that high on the neck (we prefer to use a higher string when we can instead of going that far up)
    – Kaddath
    Commented Nov 3, 2023 at 10:31

4 Answers 4

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Very likely, inharmonicity is the key. Bass strings are normally thicker, in order to have more weight per length unit which makes their resonant frequency lower. But the thicker it is, compared to its length, the less it is a one dimensional object and the less it behaves like an ideal string with harmonic overtones.

Of course, the higher you go on the fretboard, the shorter it is, but the thickness remains the same. So the ratio length/thickness get lower and lower which make the inharmonicity greater and greater.

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    The problem with the OP's video isn't inharmonicity, it's that the sample is just horribly sharp. We'll never know the precise cause, but someone f… ermm… messed up badly putting the sample set together. i'd have been sacked for getting one so wrong, back in the day.
    – Tetsujin
    Commented Nov 2, 2023 at 18:28
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    @Tetsujin have to say that I didn't listen to the sample yet :P. I trust you on that! My answer was more a potential explanation for a more global phenomenon.
    – Tom
    Commented Nov 2, 2023 at 19:43
  • Thank you for the answer. So I understand, the mechanism is that when the string is (relatively) too thick w.r.t. its length, there is an additional force preventing it from bending, which makes the overtones sharper. But I feel like it's only part of the explanation, because my impression is that that the effect is more prominent with low tuning. I know there are other sources of inharmonicity, e.g. when the vibration amplitude is too large, the overtones vibrate on a string with variable tension. But that's theory. Maybe it's unrelated to the strings, and related to hearing? Commented Nov 5, 2023 at 22:18
  • @user1079505 Maybe psychoacoustics also plays a role but note that low tuning also means less tension (with the same gauge) hence usually more vibration amplitude hence more inharmonicity. The only way to be sure is too compute the spectrum and check!
    – Tom
    Commented Nov 9, 2023 at 17:44
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There is a lot of stuff going on there. As others already said the lowest string notes are quite sharp, which is not in fact unrealistic, as intonation of the frets on these thick strings can be a bit of an issue. On a well intonated bridge this is mitigated by making the string longer, essentially making the frets lower.

But there are more things going on. As you move up the neck the length of the vibrating string goes down. This means that the string has less material to move especially for high frequencies, which makes the sound more dull. Furthermore it increases the effect of bends, making the intonation less stable. Furthermore the string is dampened at the end points, and the dampening increases with shorter length, especially with high frequencies. This makes the sound even more dull and quite short sustained. These effects also increase with the string diameter, so the lowest strings show most effect.

As Tom answered another reason is inharmonicity.

What can be done to avoid this: Quite little. If you design the string to play nicer in these areas you’d need to compromise tone or playability in low positions. Longer scales may help.

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  • Quite little to avoid this, true, usually bassists that like soloing in the more treble range tend to choose special instruments for this, like 5 strings basses with a higher string added instead of a lower B, thinner strings etc. It's rare to play the higher frets on the lower strings anyway as they are usually not easily accessible on regular basses
    – Kaddath
    Commented Nov 3, 2023 at 10:21
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As stated in other answers the reason is intonicity. There are some ways to minimize its effects, none of them perfect:

Play a fretless bass
What has worked for Jaco Pastorius might work just as well for you. The bass, today a guitar, was - originally - what is today known as "double bass", the lowest member of the violin family. The reason is that a purely acoustic instrument has to have a very big resonance chamber to project low-register sounds (with a big wavelength) on a reasonable volume and bass guitars were only possible once electrically amplified instruments were technologically available, which was around 1930. So the fretless bass is a "back-to-the-roots" kind of instrument in some way.

Get an instrument with fanned frets
There are some basses (for instance the Spector NS Dimension High Performance 5 Multi-scale 5-string Bass) which have the frets not put perpendicular to the fretboard but at a certain angle. This is called "fanned frets". It makes more of the lower strings usable while reducing the usable length of the higher strings.

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Bassically, hehe, when you play bass up high you are also getting tones from the string on the other side of the fretted finger. With sensitive pickups you can, well, pick those up also. If you just tap the frets when the bass is unplugged you can hear the other side getting louder and lower as you move higher up the fretboard.

Bass sounds pretty good up high, even in this old, low quality example:

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  • I somehow don't think this is the effect I'm asking about, but indeed in some case the sound of the other part of the string can be a real issue. Commented Dec 5, 2023 at 10:03
  • not compared to the other factors mentioned like short length affecting everything. but yeah I notice this effect when i start to tap the bass and it's not plugged in, pickups do a good job of cancelling it out but i have to wonder if it's still there even though i can't really hear it when it's cranked
    – yarns
    Commented Dec 5, 2023 at 22:03

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