and strings. This is 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 bowing styles.
All of the examples in this section show oscillograms and sound files. The oscillogram 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. The violinist 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 axis magnified. 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.
Collé is somewhat similar to saltando, except that the latter is performed with the upper part of the bow.
Spiccato is somewhat similar to sautillé.
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 the spectra 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 spectra that playing sul tasto produces a sound that is relatively weak in high harmonics.
Vibrato and the sound of the violinVibrato is an important part of the playing style and sound of the violin and related instruments, 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 the frequency 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.
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 (red spectrum). (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 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 and especially the amplitude 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 and in 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 sound coming 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. The frequencies 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 to the sound files linked above.
So, the complicated frequency response of the violin, when combined with vibrato, results in a sound is more complicated and 'alive' than a note without vibrato, and this sound is further complicated when reverberation is present, because this adds strong variation in amplitude due to the interference effects.