Sound, Tone Quality and a Little Bit of Physics

Sound might be the most immediate and definable attribute of any great musician. A plethora of terms are often used to describe it: warm, dark, ringing, brilliant, piercing, mellow, bellowing, bright, focused, rich, shimmering, spread, velvety, floating, etc. Human ears and central nervous systems probably developed the ability to distinguish sound quality so parents and children could immediately recognize each other’s voices. We can instantly identify someone by the sound of their voice, even if we haven’t heard from them for years. Likewise, a performer’s sound is their musical fingerprint. The attuned listener can immediately name Jascha Heifetz, Harry James, Luciano Pavarotti, Arthur Pryor, Frank Sinatra, John Coltrane, or Michael Jackson in just one or maybe two notes.

Lots of elements contribute to form someone’s overall sound: attack, decay, sustain, release, tone quality and vibrato. Many musicians mistake tone quality and sound to be equivalent, but the other elements can matter just as much or even more. When someone such as a conductor tells us that our sound is too bright, what exactly do they mean? Is the decay too fast? Is the articulation too harsh? Do they want us to add a little vibrato? Do they want us to use less or no vibrato? Is the sustain too loud? Or is the tone itself too strident? These are very important questions because they greatly affect what we might try to do to darken our sound.

Attack refers to the very beginning of a note. How loud is it compared to the sustain of the note? The sustain is what happens throughout the majority of the middle of a note. A crescendo or diminuendo typically refer to the sustain of the note. The decay is how quickly the note evolves from the attack to the sustain. A forte-piano attack typically involves a rapid decay, whereas a tenuto attack typically involves a much slower and more subtle decay. The release of course refers to how quickly the sustain trails off to zero at the end of a note. Collectively these might be called the “profile” of a note. Physicists call it the note’s “envelope.”

No matter what name one might give it, these parameters collectively make up a central part of what we think of as someone’s sound. However, the remaining two elements, tone quality and vibrato, tend to be more controversial for some reason. According to physicists, timbre and vibrato are essentially two aspects of the same thing: the acoustic spectrum. A simple mathematical operation known as a Fourier Transform converts sound waves from a function a time to a function of frequency. When Fourier analysis first began being applied to acoustics we learned that complex timbres were actually made up of many different frequencies, usually frequencies which were all multiples of the same fundamental pitch. Many of us refer to this spectrum of pitches as “overtones.”

However, vibrato actually does complex things to the spectrum. Most of us conceptualize vibrato as a pitch fluctuation of a single pitch. Fourier analysis shows how that is equivalent to adding more pitches above the fundamental to the acoustic spectrum. In other words, vibrato itself affects the timbre of a sound. It can add warmth, brilliance, etc. If the vibrato is fast, thin and subtle enough, it will only be perceived as a change in tone quality. This gives us yet another tool toward the goal of modifying our sound. A subtle amount of vibrato can help our sound project through a texture when necessary. It might explain why soloists use vibrato to the extent that they do and ensemble players tend to avoid using it to facilitate a section blend.

Without vibrato, the timbre of our sound is subject to the resonant spectrum of our instruments. This does not imply that all players will sound identical on the same instrument, but rather that a given instrument is only capable of producing at most its entire resonant spectrum. An instrument without higher resonant frequencies will provide great difficulty facilitating the upper register. At the same time, an instrument with lots of higher resonant frequencies will create difficulty producing warmth and width to the sound in the middle and lower registers.

In general, it is a good idea to find an instrument that has sufficient “highs” in the sound. It’s always possible to make an excessively bright sound more dark. However, it’s impossible to create higher resonant frequencies if they don’t exist. Luckily, a good way to test whether an instrument is well balanced in this way is to have other players play on it. Since an instrument’s natural resonance does not depend at all on a player, if anyone can create the kind of sound out of your instrument that you wish you could get it means that the sound is in there waiting for you to find it. On the other hand, if players you respect even have difficulty playing in the upper register or getting warmth of tone from your instrument, it means that you are probably playing on an instrument which will not afford you the opportunity to create the kind of sound you might want to have.

Sound quality is certainly a complex subject, but its comprehension is definitely a worthwhile pursuit. The ability to manipulate our sound in various ways is an invaluable part of of the job description for any performing musician.

1 Comment

  1. FiveHundo500 on January 26, 2013 at 4:29 pm

    Interesting, I never thought of applying Fourier analysis to acoustics.

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