The names of these classes of instruments suggest that the material from which they are made is significant but this is not so. Flutes are frequently made of metal and saxophones always are yet they are classified as woodwind.

(Note that I play the clarinet and saxophone but no brass instrument so my knowledge of those will be weaker.)

So, what is the defining characteristic?

  1. The form of the mouthpiece. As far as I know, all brass instruments have similar mouthpieces. Woodwind instruments have at least three distinct forms: flute / piccolo, single reed (e.g. clarinet and saxophone), double reed (e.g. oboe and bassoon).

  2. How notes between harmonics are obtained. Brass instruments adjust the length of the tube with valves or slides. Woodwind instruments open or close holes in the tube with fingers or keys.

  3. Whether the fundamental note is used: rarely on brass instruments but routinely with woodwind.

As far as I know, these properties go together. For example, I don't know of any commonly used instrument with a brass style mouthpiece but woodwind style holes in the tube for pitch control. It has been tried long ago but it was not successful: Keyed trumpet (Wikipedia).

The use of the fundamental could be significant. If it is not used then the valves just to fill in a gap of a fifth between the second and third harmonic. If the fundamental were used then an octave or more (clarinet) would be required and this might be hard to achieve with valves.

It might be hard to add valves to a wooden instruments though, of course, not all woodwind instruments are made of wood.

It has always been a puzzle to me that the holes in the tube technique produces a poor effect with brass instruments but satisfactory with woodwind instruments.

Edit: I forgot the recorder in point 1.

  • 2
    "It has been tried long ago but it was not successful" I was tried long before that, and was very successful - the cornett was considered the instrument that came closest to imitating the human voice. youtube.com/watch?v=zvu1N0k7AT8 Cornetts were commonly used in church music to take the upper parts of an ensemble of trombones.
    – user19146
    Commented Jun 25, 2018 at 12:15
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    The French Horn is an honorary Woodwind when a Woodwind Quintet is assembled. Commented Jun 25, 2018 at 13:20
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    @badjohn Don't confuse a cornett with a cornet: en.wikipedia.org/wiki/Cornett vs. en.wikipedia.org/wiki/Cornet
    – piet.t
    Commented Jun 25, 2018 at 14:06
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    @piet.t (At the English Language): Oh, now you're just being deliberately malicious.
    – Brondahl
    Commented Jun 25, 2018 at 14:18
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    @dotancohen Isn't a metal xylophone a glockenspiel? A quick Google search gets some hits but they all appear to be kids' toys. One hit was to the Wikipedia entry for glockenspiel.
    – badjohn
    Commented Jun 25, 2018 at 16:16

3 Answers 3


You might be interested to read up on the Hornbostel-Sachs classification system for musical instruments. Specifically, under this system, wind instruments are categorized as follows:

  • Edge-blown aerophones or flutes (421)

    The player makes a ribbon-shaped flow of air with his/her lips (421.1), or his/her breath is directed through a duct against an edge (421.2).

  • Reed aerophones (422)

    The player's breath is directed against a lamella or pair of lamellae which periodically interrupt the airflow and cause the air to be set in motion.

  • Trumpets (423)

    The player's vibrating lips set the air in motion.

Flutes are in category 421; "woodwinds" other than flutes are in category 422. All "brass" instruments are in category 423.

Within each of these subcategories, there are many, many, many sub-subcategories. Within category 422, there are subcategories for double reeds (422.1) and single reeds (422.2). This system therefore categorizes bassoons and clarinets as more closely related to each other than to flutes.

Concerning the use of keys on brass instruments: category 423.2 is "chromatic trumpets", for which the pitch of the instrument can be altered mechanically (as opposed to natural trumpets.) Within this category, we have

  • 423.21 Keyed trumpets – Ophicleide.
  • 423.22 Slide trumpets – Trombone.
  • 423.23 Valved trumpets – French horn, euphonium, baritone horn, trumpet, and tuba.
    • 423.231 Conical bore
    • 423.232 Semi-conical bore
    • 423.233 Cylindrical bore

"Keyed trumpets" do exist, and this attribute is (in this system) secondary to the more fundamental attribute of how the sound is produced. In addition to the "keyed trumpet" mentioned in the OP, the ophiclede, cornett, serpent, and Vladimir horn are all keyed trumpets under this system. In some sense, all of these could be considered "brass instruments" even though the last three are typically made mostly of wood.

  • Thanks. As I just said to Piet in a comment above: I just suspected and then quickly confirmed that cornet and cornett were not the same instrument.
    – badjohn
    Commented Jun 25, 2018 at 14:48
  • "Brass instruments made of wood" is no stranger than the well known "woodwind instruments made of brass".
    – badjohn
    Commented Jun 25, 2018 at 14:49
  • The alphorn is another sort of brass instrument made of wood.
    – Rosie F
    Commented Jun 25, 2018 at 18:08
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    @RosieF: As is the didjeridu. Neither one is keyed, though, so they're not quite in the same category as the ones I mentioned. Commented Jun 25, 2018 at 18:38
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    So the cornett is a keyless keyed and brassless brass instrument? Lol. Just shows to go that the nomenclature is a bit screwed. I would chuck the "standard" terminology and say that the cornett, for instance, is a buzz-lipped wooden fingerhole instrument. Commented Jun 26, 2018 at 12:45

Musical instruments are classified by the way the sound is produced. The material is immaterial and brass and woodwind instruments can both be made from metal, plastic or wood.

Woodwind instruments are those where you blow across an opening (flute), or use a single reed (sax, clarinet), or double reed (oboe, bassoon). I think pipe organs are in this class too.

Brass instruments are those where you use your lips to create the vibration, like blowing a raspberry.

Plucked string instruments are another class: guitar, harpsichord.

Percussion is where you make the sound by hitting something with something else: snare drum, piano (striking strings with hammers).

I play saxophone (a woodwind instrument made from brass) and didgeridoo (a brass instrument made from wood). I've offered the didge to some brass ensembles but this never seems to get taken up for some reason.

  • So, my option 1. As another sax player, I am quite aware that it is not the material and I have had to say many times that the sax is not a brass instrument and has more in common with the clarinet than the trumpet. Thanks for mentioning the didgeridoo, I know little about them.
    – badjohn
    Commented Jun 25, 2018 at 12:17
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    I'd give +2 for the complaint about a brass didge :-) Commented Jun 25, 2018 at 13:20
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    Pipe organs work like recorders and I'm not sure what group pipe organs are in (probably woodwinds or their own category) but recorders are definitely woodwinds, along with many other instruments that use a fipple instead of lips (flute) to create an air reed. Also: "The material is immaterial" - LOL! Commented Jun 25, 2018 at 14:43
  • @ToddWilcox I wasn't in doubt about whether the recorder was woodwind, just whether it belonged with the flute. Of course, we could consider a new class: plasticwind. The organ is interesting and so is the celesta: operated by a keyboard but very different from a piano.
    – badjohn
    Commented Jun 25, 2018 at 20:19
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    P.D.Q. Bach's tromboon, which uses a bassoon reed and bocal in place of the standard mouthpiece, should of course be considered a woodwind instrument. Commented Jun 25, 2018 at 20:46

To answer part of your question, concerning why keyed brass instruments don't work out:

The "puckered lips" which produce the note in a brass instrument create a sound pressure wave which is very nearly a square wave. By comparison, a flute produces close to a sine wave, and clarinet/sax a sort of triangle wave. Now, what the keys/holes in a woodwind do is mess up the impedance at their location along the bore, basically disallowing a peak in the standing wave pattern. Unfortunately, when this is done to a standing square-wave, (following Fourier decomposition analysis) the waveform gets badly distorted because some of the sine frequencies which make up the square wave are completely destroyed but others aren't.

In comparison, changing the length of the bore (without any holes/keys) simply changes the fundamental standing wave frequency. Any type of source waveform is "happy" to operate in this situation - consider a slide whistle, for example.

  • Thanks. That's interesting and I'll look into it. I am quite happy with Fourier Analysis, I started life as a mathematician. Indeed, it is easy to see that tube length changing will work with any type of waveform. I guess that it is not popular with woodwind due to a combination that good quality wooden valves and slides are probably harder to make and it isn't necessary as the hole technique works.
    – badjohn
    Commented Jun 25, 2018 at 14:36
  • The slide whistle may be (as far as I know anyway) the only woodwind with an adjustable length tube. Any others?
    – user33337
    Commented Jun 25, 2018 at 14:47
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    @mickeyf: Hornbostel-Sachs does have an entry for "421.121.312: Stopped side-blown flutes with adjustable stopped lower end – piston flutes." (Slide whistles are "duct flutes" under this system.) This suggests that someone might have made a "slide concert flute" that Hornbostel or Sachs was aware of. However, it's quite hard to find any information on the "piston flute" on Google, because Walter Piston had to go and write a flute concerto. Also, wikipedia seems to think that "piston flute" is just another name for the slide whistle. Commented Jun 25, 2018 at 14:59
  • Keyed brass instruments have been superseded by valve instruments, but did certainly exist, so I don't agree that keyed brass instruments don't work out. Haydn and Hummel for example wrote famous concertos for the keyed trumpet that was popular around the beginning of the 19th century, when sufficiently reliable valves could not yet be manufactured. Commented Jun 26, 2018 at 13:42
  • @mickeyf Shuttle drone bagpipes have tunable drones using slides("shuttles") to vary the length of the drones. en.wikipedia.org/wiki/Shuttle_pipes Commented Jun 26, 2018 at 14:03

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