drums

[almann1979]

okay - hope this isnt to irrelevant but...
a drum makes sound because it vibrates, it therefore has a frequency/pitch and so we must be able to allocate a note to each drum when it has been hit (all be it the note would be in a very low octave)??
now if i play the wrong notes over a backing track using my guitar i can hear that they are out of tune - so why do drums not suffer from this?? why does the sound of a drum never sound wierd even when a band play many songs in many different keys??

[Laz]

I don't know the complete answer, but I know that the drums in a kit can be out of tune with themselves/each other. Also, I did know one drummer who tuned his floor tom to resonate with a bass drone for one song, then tuned the rest of his kit to work well with that.

[jwmartin]

I don't fully understand it either, but there are a lot of overtones that happen in addition to the fundamental note of the drum, so that may cause it to "fit" better. Some drums do get tuned to a specific note, such as a timpani. My son plays them quite often in his school concert band and he usually tunes them before each song.

[Wes Inman]

Yeah, it seems wierd, but everything that makes noise is at some frequency. I have heard you can tune your guitar using the dial tone on your telephone, just sounds like a hummy buzz to me.

[pastor_bob]

There are many things that help to create the sound that you hear from a drum, and the fundamental note of the drum shell is only one. Although drums can be tuned to the fundamental note, it is not common to do so. When tuning a drum, the choice of drum heads will effect the general sound of the drum (clear heads vs. coated heads, single ply heads vs. double ply heads, or even heads that dampen the sound of the overtones). The ultimate sound of a drum will involve an interplay between the top (batter) head that is struck, and the bottom (resonant) head which will also resonate and add to the overall tone. In addition, during the tuning of a drum there are usually 2 -3 "sweet spots" of tone to choose from. What sounds best is up to the drummer to decide, based on what sounds good to their own ear, and what sounds right for the musical style being played. The most important sound to the overall sound of the band is the sound of the attack on each drum. The sound of the rhythm is more important than the exact tone of each drum.

[NoteBoat]

You can sort percussion instruments into two broad groups - "pitched" percussion and "unpitched" percussion. Pitched percussion can be out of tune just like a guitar... but pitched percussion doesn't include drums - it's the stuff like marimbas and xylophones.

The unpitched stuff, like drum sets, castanets, cymbals, etc. aren't pitched because of the way they work. And that exposes the flaw in the very beginning of your thought process:

a drum makes sound because it vibrates, it therefore has a frequency/pitch

All sound comes from vibration - a guitar string, the lips of a trumpet player, the column of air inside a flute, the movement of a sax reed, and so on. But only regular vibration has a frequency. Irregular vibration doesn't, and it's called "noise". (And I'm not kidding - that's the technical term in acoustics.)

There are a lot of reasons drums produce noise rather than pitches, but they'll basically boil down to signal reinforcement. This is what causes something in the room to vibrate when you play a certain note (it might even be the drums that start vibrating!). When that happens, you've found a resonant frequency. Non-resonant frequencies don't last - they're dampened by the object itself.

Hit a guitar string, and it rings. The frequency is resonant for the instrument. Hit a drum head and it doesn't. You get your initial boom or bang, and that's it.

The few drums that are considered pitched percussion - tympani were mentioned earlier - can be pitched by design. You'll notice several differences between a tympano and a drum from a drum set:

1. The tuners on a drum set connect the rim to the shell, or to the rim on the opposite side. When these are tightened, it affects the tension on only a part of the drum head - you have to do each one individually, and you can't really get them even. The tuners on a tympano are connected to a mechanism that is smaller in diameter - when you press down on a foot pedal, the tuners all pull down and in at the same time, allowing a fairly precise pitch adjustment. Modern tympani have the mechanism as part of the frame; older ones hid the mechanism within the bowl.

2. There's the bowl itself. Parallel heads, like those on drum sets, create a resonant chamber... the air bounces back and forth inside it, reinforcing some frequencies and dampening others. Without getting too technical about it, the more different lengths you have in a chamber, the more frequencies might be resonant. Think about how many different lengths you have in an acoustic guitar: the body depth, the upper bout, the lower bout, the length of the body, and all the angles you can get with straight lines inside that space. Compare that range to what you get with a drum, which has diameter and depth. A tympano's bowl is there to maximize the range of the straight lines you can get in the chamber.

Anyway, for those and other reasons, drums don't behave like pitched instruments. While they can sound "bad", they won't sound "off by a quarter tone".

[almann1979]

wow, i had forgotten i posted this thread, but what a good answer noteboat.

As a science teacher I remember this problem really bothering me, but that is one heck of an explanation!

thanks again Noteboat.

[Diceman]

All sounds have a pitch , even drums , but because the the sound of the drum attack is so short it is hard for the human ear to discern its fundamental pitch and therefore it doesn't sound out of tune with actual musical note producing instruments . The difference between noise and a definite pitch is time . The spoken word has pitch but does not become singing until you lengthen the time it takes to say the words . Just say " I " and then say " IIIIIIII ... " Or any other vowel .

[NoteBoat]

Diceman, you're sort of right. Sounds have four qualities: pitch, amplitude, duration, and timbre. Timbre is actually created by the interaction of pitches - a guitar sounds the way it does because the string produces more than one pitch at the same time (the fundamental and its overtones), and they waves produced by each of these pitches interact with each other. The resulting complex wave is like a signature - it's what allows us to tell a violin from a kazoo, or a guitar from bagpipes, even though they may be playing the same pitch.

What you're referring to is the 'envelope' of the sound. That's not a quality of the sound wave, but of the behavior of the wave over time. Sound envelopes are typically analyzed as periods of 'attack' (increasing volume), 'sustain' (relatively steady volume) and 'decay' (diminishing volume). Percussion instruments tend to have short attack and decay periods, with virtually no sustain.

But I would tend to disagree that a drum has a 'fundamental' tone. I'm not an expert in acoustics, so maybe there's some engineer or physicist who can give a definitive answer (which I'd certainly be interested in reading!)... but here's my reasoning:

1. Vibrating strings have a clear fundamental, because the vibration can travel in only one direction. When a drum head is struck, the point of impact will create waves radiating out that will strike the rim at different times, causing different interference as the waves are reflected.

2. A drum head is essentially a fixed plate, just like an acoustic guitar top. Ersnt Chladni's experiments with fixed plate vibration shows that a fixed plate behaves in different ways when excited by different frequencies. I see no reason to assume that a drum head won't do the same thing. In fact, just messing around with congas tells me that you can get more than one 'pitch' from the same drum head, and it'll be determined at least in part by where you strike it.

3. Because the fixed plate can be excited at different points, and a drummer - even a world class one - isn't likely to have the same point of attack on each stroke, the interaction of the reflected vibrations will vary significantly. Since the same drum sound roughly the same each time its struck, I'm thinking the result is technically noise (in an acoustic sense), and our ears aren't able to discern a fundamental because it doesn't really exist - a SINGLE drum attack might be parsed out into a 'fundamental' of x hertz, but the next attack might be x +/- 3 Hz, and the one after that could vary by six or so. If a pitch can't be reproduced, it's not the instrument's pitch.

4. If it is just noise, then why do drums sound different from each other? I'm guessing that the limiting factor is diameter: with any given starting vibration, longer distances to the rim will favor longer waves; the longer the wave, the greater the time between peaks. As a result, bigger drums will sound 'lower', because the range of noise produced falls in that part of the sonic spectrum.

In thinking this over, my gut feel is that free plates (like cymbals) behave differently. They may well have a fundamental.

Any physicists around to weigh in?

3.

[Laz]

Check this: <url>http://www.youtube.com/watch?v=v4ELxKKT5Rw </url> - arrgh, the linker isn't working for me.

This shows that the drum head has several modes that are resonant, just like a string or a reed. However, they are not pure harmonics of the fundamental, and thus probably can't exist at the same time. As Noteboat mentions, hitting the drum in a different place give a different sound. However, it's not "noise" which I consider random. The tones available during the decay period are fixed and specific. And they change with tuning (and diameter and depth of the shell).

[NoteBoat]

On wikipedia there's [url=http://en.wikipedia.org/wiki/Unpitched_percussion_instrument]this{/u], which in part discusses the "pitch" of unpitched percussion instruments.

Doing a little further reading, my gut feel seems to be right. A vibrating string produces harmonic overtones - 'harmonic' means they are multiples of the fundamental. This produces a complex wave with regular peaks and valleys that we experience as pitch.

But vibrating membranes, like drum heads, typically produce overtones that are not multiples of the fundamental. This creates a complex wave without the regular peaks and valleys - i.e., noise from an acoustic standpoint. Instrument construction CAN make a membrane vibrate harmonically, as in tympani or tablas, but most drums aren't built that way.

[Diceman]

I would like to try an experiment , one that I can describe but would be difficult for me to produce with my limited recording resources . If someone were to record the hit of a drum and take just the first snippet of sound during its attack and then combine it back to back many times on a digital recording you should be able to prove or disprove the drum/pitch argument . Does that seem a fair test ? Any takers ?

[NoteBoat]

I don't think that will prove much. The snippet during the attack would have to be very short... and the human ear can perceive pitches as low as 15-20Hz. Percussion instruments have an attack phase of about 20 milliseconds. Looping a sample that short will artificially produce the effect of a 50Hz wave - that's in the range of the bottom octave of a piano.

[imalone]

I would like to try an experiment , one that I can describe but would be difficult for me to produce with my limited recording resources . If someone were to record the hit of a drum and take just the first snippet of sound during its attack and then combine it back to back many times on a digital recording you should be able to prove or disprove the drum/pitch argument . Does that seem a fair test ? Any takers ?

Really, it's not going to be the same sound. A drum head vibrates, yes, and the different modes have a defined frequency. And yes, the different ones can all sound at the same time, but also you don't get clean harmonics in a circular membrane, unlike a guitar string where you get harmonic overtones, the different modes on a circle form different families. What really does it for defined pitch though is the decay time. It's not simply that your ears don't hear a pitch because it doesn't last long enough, it's that because the pitch doesn't exist once the sound gets short enough: the decay envelope itself smears out the frequencies. The shorter the envelope the broader the frequency spectrum is going to get, you only have a precise frequency if a pure sine wave lasts forever, in practice a few tens of oscillations is going to provide a pretty sharp peak in the spectrum, so a plucked guitar string will have a noticeable pitch. A drum, with a much shorter decay time, doesn't just have a much broader spectrum (so while there'll be a peak it's harder to discern) but also has frequency content that comes directly from the decay envelope.