What Are "Upper Harmonics" or "Harmonic Partials"?

[sulu]

I was reading a review of a bass and they mentioned too many "upper harmonic partials" or "high harmonics." What exactly are they?

When I play my bass, some notes around the twelfth fret or so give off this odd twittering behind the note itself. Am I experincing these harmonic partials? I am using flatwounds on one bass (Hofner Icon) and roundwounds on a Fender Jazz and they both produce these odd sounds behind the note on certain notes (the Icon produces louder ones). How to rid myself of these? Is it just a part of playing bass and I shouldn't even take note of it?

Thanks.

[onlyclave]

Harmonic partials a just a part of any vibrating material and you shouldn't worry about it. They are what give a bass its tone, what make a flute sound like a flute and what make different pianos sound the way they do.

When you play an open string you'll hear the fundamental tone (the lowest possible pitch) and then all of its partials. If you touch the string right over the 12th fret and play that note again you will hear the first partial (natural harmonic). If you touch the string right over the 7th fret and play it you'll hear the 2nd partial. The partials are all ratios of the fundamental.

Every single one of those natural harmonics are contained within the sound of that open string, but some are louder than others and some are so quiet the are masked by louder ones. That is what gives different basses their tone and even what makes different notes sound different on the same bass.

What you read in that review was a complaint that the strings had too much high frequency harmonic information in them and so the bass sounded "bright" or "brittle" because those pitches were overbalancing the fundamental. That could be changed by using different strings, adding mass to the neck or somehow changing the modulus of elasticity of the neck to emphasize different partials.

Most likely what you are hearing when you play above the 12th fret is the sound of your fingered note clashing against a sympathetic vibration from a different string. It sounds warbly because the strings when played that high on the neck are inherently out of tune. You could try a new set of strings or adjusting the intonation so that the strings will be in tune with each other and in tune with themselves. Also muting the other strings will help.

Don't worry about it. You can't get away from them.

[DocBop]

Hard to say what a "twittering" is could be worn frets, a bass in need of a setup, even a technique issue in some cases. I'd say take it to a repairman who can listen to you play and spot where the twittering is coming from.

[sulu]

Thanks for the replies. onlyclave, very, very informative post. Thanks. Intonation problems may be the case...I hope.

It is not an effect due to my playing technique. At times I am not even playing. I am just sounding one note to try and isolate where this twittering is coming from -- it is always from some of the high notes around the tenth through fourteenth fret. I am hating it. The notes are not clean like elsewhere on the neck. I am thinking of buying an EQ stomp box to really shape the sound to get rid of this twittering.

[mikezimmerman]

Sulu,

Try muting the strings behind where you have them fretted, towards the nut. As onlyclave mentioned, when you're fretting up high on the neck, the string can vibrate on both sides of the place you've fretted--from the nut to the 11th fret as well as from the 12th fret to the bridge when you're fretting on the 12th fret, for instance--and that "backside" portion of the string will generally be out of tune with the other half. There can also be sympathetic vibrations from other strings, which can be out of tune as well.

Another possibility is that the pickups are high enough to interfere with the string's vibration when you're fretting up high, and that can sometimes make the tone sound "wobbly".

Finally, you may just have a high fret up high on the neck that's buzzing a little bit. Hard to be sure exactly what you're hearing when you say "twittery".

Mike