Articulation and Vibrato on the Violin

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Articulation and vibrato

on the violin

Overview.

Different bowing gestures orarticulations give

the violin a range of different sounds. The

differences are chiefly in the transient sounds at

the beginning and end of the notes, and in the

envelope: the way the sound varies over time.

These are illustrated with sound files and

oscillograms.

Vibrato - a small cyclic movement of one of the left

fingers on the string - changes the pitch of the note

played. It also changes the timbre. This timbre

vibrato is very important to the characteristic sound of

the violin. This page explains why, using sound filesand graphical representations of the sound and its

spectrum.

Contents

Articulation and the sound of theviolin. A look at several different bowinggestures.

o Col legno

o Coll

o Pizzicato

o Spiccatoo Sul ponticello

o Sul tasto

o Tremolo

Vibrato and the sound of the violin. Ananalysis of pitch and timbre vibrato and their

importance to violin sound.

More detail and other links

A violin made by

John

McLennan

Articulation and the sound of the violin

In the middle of a long, sustained note, each vibration of the violin string and eachcycle of the sound it produces is nearly identical to the one that preceded it. The string

undergoes Helmholtz motion, which is shown in animation in Bows and strings. Thisis what physicists would call steady state. However, much of the interest in violin

sounds comes from the transients: the short lived effects at the beginning and end of

each note. To the violinist, these are achieved by different articulations or bowingstyles.

All of the examples in this section show oscillograms and sound files. The oscillogram
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plots the voltage from the microphone (in linear but arbitrary units) as a function of

time (measured in seconds). The voltage is proportional to the sound pressure, which

was measured one metre from the violin in a room with very low reverberation. Theviolinist is student Tricia Ho, who worked in the Music Acoustics lab in 2005.

In each case, the first oscillogram is that of the sound file. A section of it is highlighted.

The highlighted section is then shownin the next oscillogram, with the time axismagnified. Here we are not concerned with the details of the waveform, but rather with

its envelope, ie the way the magnitude of the wave changes over time.

You may wish to revise Bows and strings, Strings and harmonics orAn introductionto violin acoustics before proceeding.

Col legno

Col legno is an unusual articulation. The Italian col legno means 'with the wood'

and that is just what the violinist does: s/he plays the string with the wood of the

back of the bow, making a rattling sound on the string. In the oscillograms below,

notice the loud initial transient as the wood strikes the bow percussively. Themagnitude of the sound then decreases rapidly, because the wood does not input

energy effectively as it is dragged over the strings (unlike the Helmholtz motion

produced by the bow in its normal use).

Sound files of col legno.
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Coll

The French coll means 'glued'. The lower part of the bow (which can exert more

force) strikes the string rapidly. The sound builds up rapidly at the start of each

note, and then slows smoothly (perhaps like two surfaces with fresh glue?) beforelifting off.

Sound files of coll.

Coll is somewhat similar to saltando, except that the latter is performed with

the upper part of the bow.

Pizzicato

Pizzicato means plucked with the finger. The fleshy ball of the finger is used,

rather than the nail. Once the string is released from the finger, there is no effectivemechanism for putting more energy into the string (although violinists may try to

prolong the sound by adding vibrato with the left hand). Consequently, the sound

has a moderately large magnitude initially, but decays rapidly away.


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Sound files ofpizzicato.

Spiccato

The Italian spiccato means 'enunciated'. The bow lands percussively on the stringand remains in contact while it is drawn across a little. The attack (the initial

transient) is not so rapid as in col legno, because the bow hair is softer than the

wood. Further, there is time for the bow to provide some continuous input ofenergy before it 'bounces' off the string.

Sound files of spiccato.

Spiccato is somewhat similar to sautill.

Sul ponticello


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The Italian sul ponticello means 'on the bridge'. Bowing the string over the bridge,

it is virtually impossible to set up stable, regular Helmholtz motion, and rather easy

to excite, at least briefly, some harmonic Helmholtz motion (both are described inBows and strings). This gives a peculiar and irregular sound, with lots of high

harmonics.

Sound files of sul ponticello.

Sul ponticello contrasts with sul tasto: in the latter, the string is bowed over

the fingerboard, which is unusually far from the bridge. Sul tasto (next heading)

produces much less power in the high harmonics, which we show by comparing thespectra below. The first spectrum is for a note played sul ponticello, obtained from the

sound files shown in oscillograms above: note the weak fundamental and the strong

harmonics. The second spectrum is for the same note played sul tasto, ie with the bow

well away from the bridge. We discuss sul tasto further below, but notice in the spectrathat playing sul tasto produces a sound that is relatively weak in high harmonics.
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Sul tasto

Sul tasto means 'on the fingerboard': the string is bowed over the fingerboard, nearthe end. This position produces a sound with weaker high harmonics than normal

playing (bow between fingerboard and bridge) and much weaker than for sul

ponticello. It is rather similar to flautando, which has a sound somewhat like that

of a flute: less strong in high harmonics and with a little broad band sound as well.The spectra above contrast sul ponticello and sul tasto, so it is interesting to

compare the sound files, too.

Sound files of sul tasto.


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Tremolo

In tremolo, the bow remains in contact with the string, but the bowing direction is

changed rapidly. The rate of bowing is usually left to the performer so, in a violin

or cello section, a tremolo note will have usually have bows moving in randomphase.

Sound files of tremolo.

Vibrato and the sound of the violin

Vibrato is an important part of the playing style and sound of the violin and relatedinstruments, especially in the music of the romantic and most post-romantic periods.The regular rocking backwards and forwards of the finger on the left hand that stops

the string changes the length of the string (and also, slightly, the tension). This causes a

cyclical variation in pitch.However, as mentioned in An introduction to violin acoustics, this has the effect of

changing the timbre of the instrument as well. Briefly, the gain of the violin body is a

strong function of frequency. Consequently, even a modest proportional change in thefrequency of one of the higher harmonics of a note will change its loudness, sometimes

dramatically. So the spectral envelope of the sound varies strongly during one cycle of

vibrato. (For an excellent paper about this, see J. Meyer: "On the Tonal Effect of String

Vibrato", Acustica, 76 283-291 (1992).)Let's see how important it is. Tricia plays the note A#4 (sul A) first without and then

with vibrato.

A#4 senza vibrato. A#4 con vibrato.Here is an oscillogram of the second sound (the note con vibrato). Note the

regular changes in the envelope, which varies about six times per second - a typical rate

for vibrato and a comfortable rate to rock one's finger.
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At each of the two times indicated by the vertical dashed lines, we calculate the

spectrum of the note. These are shown below.

First, notice that the pitch is different - this is clearer for the high harmonics than for

the fundamental because, while the proportional change in frequency is the same for all

harmonics, its absolute value is greater for high frequencies.Second, notice the differences in the shape of the spectra. At the bottom of the tremolo

pitch cycle (blue spectrum),the second, third, fifth and thirteenth harmonics are at least

several decibels stronger than those of the note at the top of the tremolo pitch cycle (redspectrum). (Six decibels is twice as much power: see What is a decibel?.)

So the violin note con vibrato has varying pitch, and strongly varying spectrum. Why

does this make such a huge difference? The main reason is that human perceptions

have evolved to notice things that change in time. Further, our auditory system works
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well for human languages, which encode most of the information in the spectral

envelope. (This scientific paper has some comparisons.) So variations in the spectral

envelope are readily perceived, and they make the sound more interesting or 'alive'.

The effect of reverberation

Now all of the sounds we have heard above were recorded with a close microphone andin room with very little reverberation. This means that we hear something like the

sound that is output by the instrument. Commonly, one hears an instrument from some

distance, and in a room that provides reverberation. So one hears the direct soundcoming from the instrument added to the sound that is reflected off walls, floor and

ceiling.

In the case of a note senza vibrato, this makes relatively little difference. Thefrequencies of all the reflections are the same, so they all add up to make a relatively

simple note. In contrast, when playing con vibrato, the delayed notes may have

different frequencies, and that difference changes with time. This gives rise to complex

interference effects. In the sound files linked below, reverberation has been added tothe sound files linked above.

A#4 senza vibrato. A#4 con vibrato. (Both sounds with

reverb.)So, the complicated frequency response of the violin, when combined with vibrato,

results in a sound that is more complicated and 'alive' than a note without vibrato, and

this sound is further complicated when reverberation is present.For more information, see An introduction to violin acoustics Strings and standing waves (a simple introduction to vibrating strings). Bows and strings (a simple introduction to that interaction).

Chladni patterns (experimental results showing the vibration of the plates ofviolins). The research papers of John McLennan, PhD student in Music Acoustics atUNSW. A study oftorsional waves in the bowed string, and how they are strongly

coupled to the normal transverse waves during normal playing. How do violins change with playing and environmental changes over time?: a

report after the first three years of a long-term study. Acoustics for violin and guitar makers by Erik Jansson. And finally, yes, we felt obliged to put on ourFAQ some comments about that

hoary old question "what was the S

Speech and helium speech, with a brief introduction to the physics of the voice

This short document gives a very brief description of the source-filter model of

voiced speech used. It uses this to explain some of the most noticeable features of

helium speech, which it illustrates with sound files. If this isn't clear, see this morecomplete Introduction to voice acoustics.

The source-filter model of the vocal tract
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The vibration of the vocal folds in the larynx produces a varying air flow which may be

treated as a periodic source (A). (A periodic signal is cyclic: its motion is reproduced

after a time interval called its period. A consequence is that its spectrum is made up ofharmonics. Go to 'What is a sound spectrum?' for an introduction.) This source signal is

input to the vocal tract. The tract behaves like a variable filter (B) in that its response is

different for different frequencies. It is variable because, by changing the position of yourtongue, jaw etc you can change that frequency response.

The input signal and the vocal tract, togetherwith the radiation properties of the mouth,

face and external field, produce a sound output (C). Because the source is harmonic, wecan say that the gain of the tract (B) is sampled at multiples of the pitch frequency F0. In

the case sketched at left below, the resonances R1 and R2 can be determined

approximately from the peaks in the envelope of the sound spectrum. These peaks are

called the formants (F1 and F2). (See What is a formant?)
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Note that the detail in the spectrum is easier to see if F0 is low, e.g. for a low pitched


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man's voice (diagram at left), than it is for a child's voice - shown at right.

The lowest resonance is determined to a considerable extent by the end effect of your

mouth: if you lower your jaw, R1 rises. R2 is affected by the jaw position too, but it isprimarily affected by the position of the constriction inside your mouth. Moving your

tongue forwards and backwards changes R2 (and also R1, but to a lesser extent). Maps of

(R1,R2) for various accents of English are given onSounds of World English.Nearly all information in speech is in the range 200 Hz - 8 kHz. (The telephone carries

only 300 Hz - 4 kHz but speech is reasonably intelligible.) The pitch is determined by

the spacing of harmonics as much as or more than by the fundamental. Thus you can tellthe pitch of a man's voice on the phone even though the fundamental of that signal is not

present. Note that the size of the vocal tract (~170 mm long) gives resonances around

500 Hz and above. In fact a closed tube of this length is a functional approximation of the

tract for the vowel "er" as in "herd". For this 'neutral' vowel, the first five resonances ofthe author's vocal tract are indeed at values of about 500, 1500, 2500, 3500 and 4500 Hz.

What helium does to speech

You can investigate the model described above by changing the speed of sound. Inhaling

helium changes the frequencies of the resonances, and therefore of the formants they

produce (See What is a formant?). As you would expect from the model above, it doesnot change the pitch, which is determined by the tension, mass and geometry of vocal

folds, and some other effects. It does however change the timbre. In speech, you may

have the illusion that the pitch has changed because one doesn't think much about pitchwhen listening to speech. To make it clear, you can sing with and without a lung

containing a substantial fraction of He and listen.Warnings: He is suffocating and

conducts heat well. After one inhalation of He, breathe air normally for a few minutes. Ina gas cylinder, He is under high pressure. Do not inhale directly from a gas cylinder. Fill a

toy balloon and inhale from that.Okay, having read those warnings, you might not want to try. So I've put the recordings of

my experiment below.

The first diagram shows

a schematic picture of thespectrum (power vs

frequency) for the sound

of the voice made with aparticular configuration

of the vocal tract filled

with air. The solid line is the spectral envelope; the vertical lines are the harmonics of the

vibration of the vocal folds. The second diagram shows the effect of replacing air withhelium, but keeping the tract configuration the same (i.e. trying to pronounce the same

vowel as before, but with a throat full of helium). The speed of sound is greater, so the

resonances occur at higher frequencies, as do the formants they produce: the secondformant has now been shifted right off scale in this diagram. The flesh in your vocal folds

still vibrates at the same* frequency, however, so the harmonics occur at the same

frequencies.
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What does this sound like? Obviously the helium makes a big difference to the sound of

the voice.

Audio File File Format

Ordinary Speech

Helium Speech

Pitch in Air

Pitch in Helium

If you do the experiment with someone who has some experience with singing or music,

(and if s/he doesn't laugh too much on hearing helium voice) then the pitch will be the

same in the two cases. The pitch is determined by the frequencies of the harmonics and

these have not changed*. The speech does, however, sound 'like Donald Duck'. There is

less power at low frequencies so the sound is thin and squeaky. This alteration to thetimbre changes vowels in a spectacular way. Although we can understand whole

sentences (using contextual clues) we find that individual vowels are very difficult toidentify. (By the way, an articulate but otherwise standard duck would have a shorter

vocal tract than ours so, even while breathing air, Donald would have resonances at rather

higher frequencies than ours.)* If you keep the muscle tensions the same, that is, the frequencies will not change

much. There could be a small change because the less dense He loads the vocal folds

a bit less than the air, but this effect is slight. The effect on the resonances is large,

however. Its size depends on how pure the He in your vocal tract is.

More about voice acoustics

The very brief account above addresses only vowels. OurIntroduction to voiceacoustics is a much broader introduction. It provides both a simple overview, and a

rather more detailed account. Throughout, it suggests a range of experiments for the

reader to try none of the others involving helium.
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Articulation and Vibrato on the Violin

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