What Is a Mute? Changing an Instrument's Voice Rather Than Its Volume

Sound from an instrument contains a fundamental and a set of higher partials whose relative strengths produce its characteristic tone. A mute interferes with the radiating surface or the air column and does so unevenly across frequency, damping some partials more than others, which alters the balance and therefore the timbre. On a brass instrument a mute is inserted into or placed over the bell, obstructing and reshaping the air path, and different designs emphasise different regions of the spectrum, producing sounds described as nasal, buzzing, distant or metallic. On a string instrument a clip fitted to the bridge adds mass, which reduces the bridge's ability to transmit higher frequencies to the body and gives a veiled softer tone. On a piano the soft pedal shifts the action so that hammers strike fewer strings or with a different part of the felt, changing colour as much as level. In each case the volume reduction is a side effect.

Brass mutes are the most varied and jazz developed most of the vocabulary:

• •Straight mute, conical and inserted in the bell, producing a bright pinched sound and the standard orchestral option
• •Cup mute, with a cup covering the bell, giving a softer more distant tone
• •Harmon or wah-wah mute, sealing the bell entirely so all sound passes through a stem, producing the thin buzzing voice associated with Miles Davis, and manipulable by covering the stem
• •Plunger, an ordinary rubber sink plunger held over the bell and moved, which produces the speaking and crying effects of early jazz brass
• •Bucket mute, clipped over the bell and filled with absorbent material, giving a very soft muffled tone
• •Practice mutes, which are designed purely to reduce volume for rehearsal and which deliberately sacrifice tone, and which are therefore the exception to the rule

Strings use a small clip or rubber device on the bridge, notated by a direction to mute and removed by a direction to play openly, and orchestral scores use it for colour rather than for balance, since a muted string section has a distinctive hushed quality that no reduction in dynamic reproduces. Practice mutes of much heavier material exist for domestic rehearsal and change the tone drastically. Timpani and other percussion are damped with cloth or hands, which shortens the ring as much as it softens. Guitar uses palm muting, resting the picking hand on the strings near the bridge to shorten sustain and produce a percussive chunk, which is fundamental to rock and metal rhythm playing, and fretting-hand muting to silence unwanted strings. The piano has no mute in the same sense, with the soft pedal altering the mechanism and the practice rail on upright pianos interposing felt, which is closer to a true mute and sounds correspondingly poor.

Fitting a mute changes more than tone and players have to compensate. On brass instruments a mute alters the effective length and shape of the air column, which shifts pitch, generally sharp, and by an amount that varies between mutes and between registers, so a player fitting one must adjust embouchure or use an alternative fingering. Response changes too, since resistance increases and quiet playing becomes harder rather than easier, which is the opposite of the intuitive expectation and is a recurring frustration for students who assume a mute makes soft playing simpler. On strings the effect on pitch is negligible and the effect on response is real, since the added mass at the bridge changes how the instrument speaks and requires a slightly different bow contact. These are the reasons that playing well with a mute is a distinct skill rather than the same skill applied through a device.

Muting is a colour instruction rather than a dynamic one and scores treat it that way. Orchestral writing uses muted brass for distance, for menace and for a metallic edge, and muted strings for a veiled quality used constantly in film scoring for interiority and memory. Changes take time, so a composer must allow bars for a player to fit or remove a mute, and failing to do so is a recognised amateur error that a professional part-writer avoids. Jazz treats brass mutes as a core part of a player's identity, with the plunger and harmon sounds so strongly associated with particular performers that using them is a reference. Recording introduces its own considerations, since a muted instrument has a different directional pattern and requires different microphone placement. And the availability of a mute has shaped repertoire, since passages requiring a particular colour could not be written before the device existed.

A mute damps some partials more than others, which changes timbre, and the reduction in volume is a side effect rather than the purpose. Brass mutes give distinct voices, with the harmon sealing the bell so everything passes through a stem and the plunger producing speech-like effects. Scores must allow time to fit and remove them, and forgetting to is a recognisable amateur error.