Is there a broader term for instruments, like the gong, whose volume briefly increases after being sounded instead of immediately decaying?

Question

For most instruments, their sound immediately begins to decay after they first sound. When you strike a piano key, for instance, the loudest sound is at the very beginning, after which the sound immediately dies out.

But some instruments, like the gong, briefly increase in volume before the sound begins to decay.

Is there a term for these types of instruments, or perhaps for this acoustic property? I'm looking to find other instruments with this characteristic, and I'm hoping a term will help me do that.

Answer 1

That's weird... apparently there's no English term for this exact phenomenon, but there is one in German: Einschwingvorgang (pronounced eyn-shving-fore-gung). Wikipedia wants to have it translated with transient, but I disagree. A literal translation would be “oscillation start process”, i.e. it describes the start of an oscillation which then just goes on, whereas a transient describes an event that's triggered at a discrete moment in time and also has only influence over a limited amount of time (like a piano note).

^{[Ok, of course the gong is in fact triggered at a discrete moment and the tone doesn't last forever... but bear with me. In case of the gong, both einschwingung and transient apply!]}

“Slow attack” is how synthesizers may simulate einschwingung, but it's not really a good approach. An ADSR attack works by having the oscillator start immediately in full swing, but only gradually turning up its signal (envelope). This does work well to simulate transients, but not einschwingvorgangs, because in these is it the oscillator itself that only develops its vibration over time.

Now, synthesizers also use the envelope technique to simulate decay, which is in physical instruments also a behaviour of the oscillator itself. Why then am I making a fuss about einschwingung being more than just attack?

Einschwingung is physically related to “decay in reverse”, indeed it is often described this way – but IMO that's a bit misleading. Decay is (or at least, can be) a purely linear effect, for example a decaying piano string is for all practical purposes linear. It is the linearity that guarantees the whole process can be simulated by a non-decaying oscillator followed by a time-dependent amplifier/filter, because for linear behaviour putting in a mixture of modes at the start is equivalent to putting in each individual mode and mixing the results^★.

But if einschwingung were linear (more precisely, LTI), the volume would either just keep on growing and growing until infinity, or reach a maximum amplitude and decaying back to zero before growing again, repeat... this is clearly not how instruments behave (though the former is a pretty good description of feedback in amplified audio).

Instead, the einschwingung in gongs and also in bowed strings and many others is a fundamentally nonlinear effect. That means, you have energy transfer from some “quiet” mode into a more audible one. On a piano/guitar string this is not possible because it's too linear – it would be the equivalent of playing a 2nd harmonic on a guitar string and it then changing into a 3rd harmonic^†. But that is essentially what happens in a gong: the beater initially just perturbs it in a very low-pitched mode that contains a lot of vibrational energy but is almost inaudible, but this energy is then transported into the much louder white-noise-ish modes.

In bowed strings, it is the bow-hair–string contact that behaves nonlinearly. Specifically, increasing the sliding force 2× does not increase the sliding speed 2×. Instead, up to a point the string sticks completely to the rosin and then it's suddenly released. At the very start, the result of this isn't really an oscillation at all but more of a random/chaotic scrape – but then resonance kicks in and creates a phase-locked loop, which is what creates the actual violin tone. But the einschwingvorgang, or the transient that results from it, isn't really a tone at all and therefore can't be convincingly simulated with ADSR envelopes. It can only be simulated with nonlinear elements – the simplest of these are ring modulators and frequency modulation. The best known synth to use this approach is the DX-7.

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^★_{One way to see that a gong is non linear is to compare striking it a couple of times gently and each time waiting for the low-pitch mode to decay again, which striking it with the same intensity in quick tremolo. If the gong were linear, then the tremolo would just sound like each of the single strike in succession, but instead it will actually change its character and develop the swoosh that you also get from a harder hit, because the small hits accumulate until enough energy is in the system so it becomes nonlinear and feeds into the high-frequency modes.}

^†_{Pianoteq actually has a feature that simulates this kind of behaviour – if you turn it on, your piano will suddenly sound like steel drums!}

Answer 2

I’m not sure if there a conventional term for it but from a waveform standpoint the term would be that it has a slow attack and low transient. Another instrument with a similar characteristic would be a cello when bowed. As opposed to instruments with a fast attack (I.e. guitar, piano, drum)

Transient sometimes referring to the initial burst of energy from equilibrium to the crest of the wave and its relative height to the surrounding waves; or as you have described :

When you strike a piano key, for instance, the loudest sound is at the very beginning, after which the sound immediately dies out.

Would be an example of a transient wave

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Consider the image showing the piano with a high transient, fast attack and rapid decay next to a steady wave created by a violin which can be considered to have a low transient and a slow attack much like a gong would produce.

Answer 3

@Timinycricket has it right: slow attack / fast attack. The terms are relative, not exact. Here is some supplementary information.

1. To describe a gong, or other instrument's sound, the closest musical term is timbre, and the acoustical term is sound envelope.

2. There are (were) at least two timbre-based taxonomies of musical instruments:

The eight-fold system of eight sounds or timbres (八音, bā yīn), from [the Yo Chi (record of ritual music and dance)], occurred gradually, and in the legendary Emperor Shun's time (3rd millennium BC) it is believed to have been presented in the following order: metal (金, jīn), stone (石, shí), silk (絲, sī), bamboo (竹, zhú), gourd (匏, páo), clay (土, tǔ), leather (革, gé), and wood (木, mù) classes, and it correlated to the eight seasons and eight winds of Chinese culture, autumn and west, autumn-winter and NW, summer and south, spring and east, winter-spring and NE, summer-autumn and SW, winter and north, and spring-summer and SE, respectively. (SOURCE: Wikipedia)

The T'boli [people] of Mindanao use three categories, grouping the strings (t'duk) with the winds (nawa) together based on a gentleness-strength dichotomy (lemnoy-megel, respectively), regarding the percussion group (tembol) as strong and the winds-strings group as gentle. The division pervades T'boli thought about cosmology, social characters of men and women, and artistic styles. (SOURCE: Wikipedia)

3. "Envelope Model of Isolated Musical Sounds", by Kristoffer Jensen, contains images of the sound envelopes of various instruments (sadly, no gong). (from Proceedings of the 2nd COST G-6 Workshop on Digital Audio Effects (DAFx99), NTNU, Trondheim, December 9-11, 1999)

4. You might enjoy this literal and metaphysical description of the gong and its sound envelope given in the article "Creating the Sound of the Gong", from Gong Yoga Newsletter (April 2019). (The article includes an illustration, but not a measured graph, of a gong's sound envelope.)

Answer 4

In synthesis, the magic letters ADSR get bandied around a lot. They represent a sound envelope, which every sound, particularly musical instruments, have. They're the basic breakdown of a sound.

Every sound will start somewhere! That's the Attack part. It may be immediate, as in a snare drum, or stridently played violin note, or slow, as in a swelled note on a violin. Sometimes it's the intrinsic instrument, sometimes the way the note is produced by the player.

The Decay comes next - how soon the sound starts to fade away, as most sounds will. Although an organ note could be said to have no Decay, but lots of sustain - until the key is let go).

The decay turns into Sustain, where some notes will last seemingly for ever, while others die quickly.

Release is the actual end of the sound, which woud make a note staccato (quick release), or legato (slow release).

The gong would probably be described as a slow attack, a very slow decay, a long sustain (unless damped) and a slow release (same again).

There are interesting graphs which compare various sounds/instruments.

Answer 5

An informal term that musicians might understand is ‘built-in crescendo’.

On an instrument with a volume level that's (mostly!) controllable throughout each note, such as a violin or voice, the musical term for this would be a crescendo through (the first part of) the note.  It's stretching the term to use it where it's built into the instrument instead of applied by the musician, but I think most musicians would find it clear.

(Synthesiser programmers would of course use the technical term ‘slow attack’, as per other answers.  But that might be less well understood by others.)

Answer 6

A note that gets louder is exhibiting a volume swell: it is swelling or "blooming".

That doesn't identify a class of instruments, but if you were writing some article on music and defined a term like "blooming instrument" for the reader, it would be easy to understand.

Answer 7

I would call this "delayed onset". I've looked and can't find the term. There's a wiki page Onset (audio). Otherwise, related I found the other day Philip Tagg:

In 2011 Tagg started working for the reform of music theory terminology ... that the denotation of non-notated musical structures, rarely covered in conventional music theory, needs urgent attention.

Answer 8

To answer the specific question in relation to the scientific literature, no, there is most likely no specific term reserved for this time delayed phenomenon.

I just now reviewed a few pioneering papers at the Journal of the Acoustical Society of America (JASA) and found mention of the time it takes for sound to mature, but without a specific term other than "a characteristic time." In one paper on the Balinese Gamelan gong, researchers focused on describing the distinct acoustic beating called ombak when struck. Ombak doesn't contain any reference to a time delay in buildup of sound, and can be explained at least in part by the self beating of closely spaced frequencies within a given region of the gong's vibration.

I'm sure there are terms among gong enthusiasts. Apart from a specific name, and for the interest of some, I will add a general physical explanation of the phenomenon, which will not contain the very complex physical details, and I think it differs from others I've read here.

The sound we hear is a direct result of the power density of air vibration that strikes our ears. Any sound source radiates sound energy that results in an integration of all the air vibration that occurs over it's entire surface. The integrand in that integral is the product of vibration amplitude and material area.

The initial strike of the gong causes a relatively small fraction of its area to vibrate at a relatively high amplitude. Because of the physics of the vibration in the gong material involving shear ant tensile stresses, the initial localized vibration slowly propagates throughout. Slow with respect to the periods of oscillation of the various frequencies excited. A complicated interaction - which becomes increasingly nonlinear with larger amplitudes - among the different regions excites various resonant frequencies of different regions, which incidentally are not harmonic multiples of frequencies within a given region or frequencies of other regions.

The regions I speak of are separated by vibrational nodes. These nodes provide somewhat of a barrier to the propagation of the vibration, but not perfectly, because they in themselves are not perfectly isolated nodes. With the gong struck at the center by a soft mallet, the vibration soon travels to the gong periphery.

As the material vibration extends, the total area that radiates sound greatly increases. The integrand in the integral mentioned above thus increases because of the increased area, and also because the vibration amplitudes are facilitated by resonance in the various vibrational regions. The net result is that much more acoustic energy is radiated.

There may also be the effect of perceived loudness because it's possible that our hearing is much more sensitive to some of the vibrational frequencies now occurring over the increased radiation area.

Energy is conserved. The total gong does not vibrate with more energy than the energy imparted with the first strike. It's only that, because of the peculiarities of the physical vibration of the gong material, the integral - which is a function of time - becomes larger, radiating more acoustic energy to our ears.

At the lowest amplitudes, the vibrations are largely linear, and nonlinearities become more pronounced and produce the most interesting sounds. In acoustic physics, a gong is classified as a thick plate. Thick plates, like bars such as cantilevers vibrate linearly at low amplitude. The fact that they do not produce harmonic overtones like a vibrating string for instance is a result of the physics. The speed of sound in the material depends on the frequency of the wave, and the complexity of all those frequencies and beats of frequencies hitting our ears may have significant modification according to our perceived loudness. In some cases, the motions can be called chaotic. There is a question of course whether large amplitude nonlinear vibration affects the time delay in volume that we are concerned with here, and that may indeed be the case.