Guitar Sound – Overtones, Balance, Presence & Sustain

Majority of the texts on music available on the internet, describe the sound of the instruments through words like volume, sound tones, timbre, attack, decay, overtones, balance, presence, dynamic range, sustain, projection, wraparound, etc.

 While the true meaning of these will be absolutely clear to you only by playing the instruments and looking for them. This article aims to explain the associated concepts so that you can learn to hear and look for these qualities in different guitars and have the vocabulary to describe your experience.  

Sound Characteristics.

Sound produced by any musical instrument is characterized by pitch, loudness and quality. Pitch is related to frequency of the sound and loudness to the amplitude. Sound quality, also referred as timbre, relates to the distinguishable characteristics of the tone.

Timbre and Harmonic Content

Timbre depends on harmonic content and dynamic characteristics of the sound. Harmonic content means the number and relative intensity of higher harmonics in the sound. It is the single most factor to determine, how sustained the tone is.

Dynamic characteristics are defined by attack, decay, vibrato and tremolo. We shall discuss dynamic characteristics later in the article.

Simple fundamental frequency sound is very simple and boring, unless spiced up with harmonic content .

So, let us now look in detail, at harmonic content of the sound produced by the guitar string. This is essential to understand the effect of location of pickups on the tones produced by them.

Frequencies Of Sound Produced By Guitar Strings

When a guitar string is plucked, various vibration frequencies are produced, which travel through the string together. These frequencies are dependent on mass, tension and length of the strings.

Length of string for any guitar is the distance between bridge and the nut. These points, where strings are fixed and do not have any vertical movement are called as nodes. In contrast, points of maximum vertical movements are called as antinodes.

The lowest of the frequency at which the string vibrates is called as its fundamental frequency. It is produced when you pluck an open string. The fundamental frequency is the perceived pitch

Other frequencies produced are multiples of this fundamental frequency and are called as harmonics or overtones. They give fundamental pitch different tonal qualities.

Overtone Series 1

Commonly, the fundamental frequencies for six guitar strings from thickest to thinnest ones, with standard tuning, are given in table below

String

Fundamental Frequency

E2

82.4 Hz

A2

110 Hz

D3

146.8 Hz

G3

196 Hz

B3

246.9 Hz

E4

329.5 Hz

If you halve the length of the string, you double the frequency. So, if you lightly press the E4 string at 12th fret, the pitch produced is of second harmonic. We can get third harmonic by fretting at the 7th fret. We are creating nodes at these frets by pressing string there.

Overtone Series And Timbre Of Sound

The sound produced has many frequencies. As, all these frequencies are harmonics of fundamental frequency, the overall pattern repeats itself regularly. If fundamental frequency is 330 Hz, pattern will repeat 330 times every second.

In the time, the fundamental frequency completes one full cycle

  • Second harmonic (First Overtone) completes two cycles
  • Third harmonic (Second Overtone) completes three cycles
  • So on …

Overtones are just changing the shape of the sound wave. Hence, we can conclude that

  • Pitch is determined by the fundamental frequency.
  • Overtones changes the waveform making sound more complex and richer.
  • Overtones are not separate notes but determine the timbre of an instrument.

This  is the essential reason, due of which different instruments sound differently, even if playing the same note. The difference is in the overtones produced by them and hence, their timbre.

Even, the place of plucking the guitar strings makes a big difference.

Volume

Volume tells us how loud or quiet your guitar is. It is also called as magnitude or amplitude or intensity of sound.

The loudness of any sound is perceived by its Sound Pressure Level (SPL). Louder sounds carry more energy and corresponds to higher sound pressure.  

Sound pressure is the deviation in air pressure from its normal atmospheric value as a result of a sound wave. SPL is measured on a logarithmic scale as a ratio of actual sound pressure to a reference sound pressure (RSP) in decibels (dB). The reference corresponds to hearing threshold of a healthy and young ear.

We can use Decibel Meter to find out the loudness of any guitar. However, other qualities of sound, such as presence and balance (which we will discuss later in the article) play a major role in perception of loudness of any guitar.

For an acoustic guitar, volume depends on the freedom of guitar top to vibrate on being driven by the guitar strings.  Other factors which influence volume are

  • The quality, thickness, bracing and finish of the top wood determine the volume potential of any guitar. Rigidity of back and sides has big influence on the air chamber resonance.
  • As a general rule, heavier strings, produce louder sound. However, we may observe a case of diminishing returns, if we provide heavier strings on light and delicate guitars.
  • In large acoustic guitars, heavy vibrating top and large sound chamber capable of reinforcing vibrations, both work together to produce a very loud sound.
  • Mass of neck and headstock also impacts the instruments capacity to absorb power from strings.

Volume can be different between high and low strings. But an instrument, which is genuinely loud will be loud across the entire range, not just for some notes.

Presence

Presence is the quality of guitar which makes it sound full and louder than what the readings on the Decibel Meter suggests. Measurable volume is indicative of the capability of an instrument to outshine others. It also tells the distance from the instrument, till which the sound will be heard clearly.

Presence is more psychological. It makes you feel surrounded by sound in a closed setting. We can say that a guitar has good presence if even soft sounds are equally satisfying and tone quality does not go down with volume.

Presence gives you sensation of fullness and implies good tone quality. It has a close relation with balance and sustain, which we will study in later sections.

Efficiency of the guitar top contributes a lot towards perception of presence. In fact, guitar that depends more on its top to produce volume in comparison to resonance of its air chamber, has more presence.

Dynamic Range

Dynamic range can be defined as the difference in SPL between the softest and the loudest sounds.

If you want to make you guitar sound louder, you can pluck it harder. But this will work only up to a certain point. Beyond this, plucking harder will not result in any further increase in volume. Similarly, if you play soft beyond a point, the sound may become inaudible or loose clarity.

A great guitar will produce different and great sounds when you play it very softly, softly, medium and hard. On an instrument with good Dynamic Range, you can clearly bring out the meaning of the song, through soft and loud sections. Playing quietly requires great touch and control.

Dynamic Range is linked with volume and fullness and like these properties depends on the top of guitar.

Separation

If you play many notes simultaneously on you guitar, are you able to hear each note clearly or distinctly? If yes, your instrument has the ability of separation. If the resulting sound lacks focus, or is cloudy and fuzzy, your guitar lacks separation.

If you play a chord, are individual strings audible or sound from all the strings blend together? Ability to hear and perceive separation comes with experience.

Building guitars with good separation is difficult and may be found in very good and expensive guitars.

Balance

It is also known as the Timbral Balance. It tells you if the guitar, in terms of volume and fullness, is bass heavy, treble heavy or balanced between the two. 

In other words, in a balanced instrument, both high and low notes play loud and full. The instrument is not biased towards any particular frequency.

Bass Heavy Guitars

Guitars which are bass heavy, meaning that the balance is tilted towards the bass (lower) frequencies are also called “boomy”. These instruments give full sound in bass-note / strum style as the only accompaniment to the singer or in bluegrass band.

Treble Heavy Guitars 

Playing in quiet surroundings and styles with melodic fingerpicking require guitars with balance tilted towards higher frequencies.

Balanced Guitars And Factors Affecting The Balance

In today’s time, slightly bass heavy guitars are preferred. To beginners also they sound better than the treble heavy ones.

Perfectly balanced guitars are harder to make and play. In these guitars, you need to control the relative volume of low and high strings through touch only. The main factors effecting the balance are

  • Size: Balance in reality more a function of size of the guitar. Large sized guitars are mostly bass heavy, while smaller ones have dominant highs. E.g. Dreadnoughts are very boomy.
  • Wood: Rosewood is more boomy than Mahogany
  • Size of Sound hole:  In Large Sound hole instruments, the balance is tilted towards high frequencies.

Sustain 

Sustain is the property of any instrument which gives us an idea of the duration, any note will continue to sound after being played. Sound usually has two components attack and decay as defined below.

Attack

Plucking of a guitar string, results in a rapid increase in the peak amplitude of the vibrating guitar string. This phenomenon is known as attack.

Decay

Once the guitar string is plucked and left, the amplitude of vibration gradually decreases over time till it stops vibrating. This phenomenon is named as the decay of vibrations. Both attack and decay are demonstrated in the attached image.

The attack-decay envelope gives you a clear idea about the speed with which the sound reaches its peak value, decays and stops eventually. It takes several milliseconds to reach the peak volume. The duration of the envelope and its shape has a big impact on the timbre of the instrument.

Instruments that produce sound with very fast decay are said to have poor sustain. These instruments do not have the ability to hold long notes and chords. In very simple terms, you can think sustain to be the ability of strings to sustain vibrations. If string can continue to vibrate for longer duration, the instrument is said to have more sustain.    

Sustain is result of a system comprising of strings, bridge configuration, nut, woods, action (height of the strings), vibrato, string gauge etc. There is a divided opinion about the role of wood’s mass and its contribution to sustain.

As per first group, lighter guitars with thinner woods are good for sustain. Old SG’s with thin mahogany body is often cited as an example in favor of their view.

They feel that energy of string vibration causes the lighter tops to resonate. Resonating top transfer back the energy to the string as a feedback loop, causing them to vibrate longer. Argument against this logic is that guitar made of soft basswood or Alder do not have much sustain.

Air chamber also produces an echo-like sustain which is a less clean sound.

Second opinion is based on 1970s Les Paul guitars with thick Maple tops and heavy Mahogany bodies. Their opinion is, dense and rigid material does not absorb much of the string energy, allowing it to vibrate for longer duration.

Based on this concept, Volume and Sustain are qualities that are opposite in nature. Volume depends on the flexibility of the guitar top, whereas sustain requires more rigidity.

In line with this concept, Taylor guitars, introduced V-Class bracing in 2018 to resolve this compromise. They have provided a support along the direction of strings to make the center of guitar more rigid. This allows strings to retain their energy.

V-class bracing allows the sides of the top of the guitar to be more flexible and generate louder volume.

Guitars with thicker strings will have more sustain as these strings have more mass, energy and inertia. In wound strings, Flatwound strings have more sustain because fundamental frequencies in these have more energy.

Projection And Wraparound.

Projection provides us a measure of how well a guitar forwards its sound to audience or microphone. Guitar with good projection sounds full to the audience, in addition to letting your fellow players know what you are playing.

Wraparound, on the other hand, is the ability of the guitar to wrap its sound around you. It allows you to hear yourself while playing in a group and be satisfied with your efforts.

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