Course:Phys341 2020/Voice harmonization

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What makes certain voices sound good together? What does it mean to harmonise notes and voices? With these questions in mind, I intend to explore what makes voice harmonisation and the concept of consonance and dissonance.

The Human Voice

Fig. 1 An animation showing the vibration of the vocal folds

To start with, we need to consider the origin of the human voice. Where does our singing voice come from? The sound that we come to interpret as the human voice, is the result of the vibration of the vocal folds (which are otherwise referred to as vocal cords). These vocal folds are muscular tissue [1] which can be found in the larynx, in which these vocal folds vibrate as air from the lungs are forced through them, which then creates a buzzing sound.[2] This action can be seen through the figure shown on the left (Fig. 1) in which shows how the vocal folds are creating a vibration as the air is pushed through them, causing them to come close to one another then, disperse away from each other. From this diagram, it can be seen that as the vocal folds vibrate, they vibrate at acoustic frequencies, meaning that we have oscillating valve[1].

As a result, when the vocal folds are stretched slightly, the tension in the vocal folds increases, resulting in high pitched sounds; furthermore, sounds of lower pitches are produced when these folds are shorter and less tense[2].

Fig. 2 A labelled diagram of the human vocal tract

The Vocal Tract

The vocal tract primarily acts a resonator and as a filter for all parts of the sound created by the vocal folds[3]. The length and shape of the vocal tract affects timbre [4]. Think of this, the vocal folds in the larynx create a repeated pattern of pulses in which the vocal tract acts as an airspace which likes to vibrate[4]. Therefore, when the sound pulse hits the vocal tract, the air resonates at the preferred frequency of vibration; thus, the sound that emerges from the mouth has the same pitch but produces a different timbre to the sound produced by the vocal folds[4].

In Fig. 2, the part which is labelled the voice box, is also referred to as the larynx, which is where the vocal folds are located. The purple areas of the digram highlight the two primary air passages: the nasal cavity and the oral cavity. Additionally, as mentioned before the length and shape of the vocal tract can affect the timbre and a few ways in which the vocal tract can be manipulated is through the manipulation of the larynx, which is referred to the voice box in Fig 2. When one yawns, the larynx is pulled down, extended the vocal tract, which creates a lower pitch of the air, which are also referred to as lower formant frequencies[3]. Moreover, when one swallows, the larynx is pulled up, shortening the vocal tract, which creates a higher pitch of the air, which are also referred to as higher formant frequencies[3]

Vocal Harmonisation

Vocal harmonisation refers to the way in which multiple voices work together to compliment the fundamental voice, this can be further understood through the example of the orchestra, where different instruments with different range in pitches work together to compliment the main melody. In physics, it can be seen that harmonising works by playing notes that are complimentary to the main fundamental note, thus to produce consonance.

The Four Main Voices

There are four main voices that can be found in choirs or musicals: Soprano, Alto, Tenor and Bass. What makes these voices harmonise well is difference in their range and the unique set of notes each voice can reach.

The ranges shown below the two octave range in which these voices can reach, from the lowest note they could reach to the highest. Soprano and Alto are typically common among females, while Tenor and Bass are common among men, this is because as mentioned before the length of the vocal folds play a role on the pitch of one's singing voice. So typically, female vocal folds range from 12.5 millimetres (mm) to 17.5mm long, while males have longer vocal folds ranging from 17 to 25 mm.[5] Moreover, to compare the voice to other instruments such as the guitar, thicker and longer guitar strings result in slower vibration when plucked and henceforth produce a lower pitch; this is similar to the vocal folds, whereby the thicker and longer the vocal folds are, the vibration produced by the vocal folds will be lower[6]. As a result, this is why men have a deeper voice compared to women due to their thicker and longer vocal folds [6].

Soprano

Fig. 3 The vocal range for a soprano voice using piano keys to visualise the range. The green represents the range between the lowest and highest note that is sung by one who possesses a soprano voice. The yellow key on the piano represents the middle C on the piano.

Soprano voices is the highest voice out of the four, in which it is most commonly found within females. The range of soprano voice, which is visually illustrated in Fig 3., which can be seen above, begins from the middle C (C4) and reaches as high as C6.[5]

Alto

Fig. 4 The vocal range for an alto voice using piano keys to visualise the range. The green represents the range between the lowest and highest note that is sung by one who possesses an alto voice. The yellow key on the piano represents the middle C on the piano.

The alto (or contralto), which refers to the lowest vocal range found in females. The vocal range of an alto voice is F3 (which refers to the F note below the middle C (C4), which is highlighted in yellow in Fig. 4 and extends all the way till F5[5].

Tenor

Fig. 5 The vocal range for a tenor voice using piano keys to visualise the range. The green represents the range between the lowest and highest note that is sung by one who possesses a tenor voice. The yellow key on the piano represents the middle C on the piano.

The tenor voice, on the other hand, is considered the highest range of vocals a male can possess. Fig 5. illustrates the range for a tenor voice, with the lowest note being C3 extending till C5. In this manner, it is interesting to see the overlapping range of the tenor and soprano.

Bass

Fig. 6 The vocal range for a bass voice using piano keys to visualise the range. The green represents the range between the lowest and highest note that is sung by one who possesses a bass voice. The yellow key on the piano represents the middle C on the piano.

Bass is the lowest vocal range and is predominantly sung by male voices. Fig. 6 illustrates the vocal range for bass, in which the bass voice is able to hit as low as E2 and as high as E4[5].

These are the most common voices one would hear when harmonising in a choir or a musical, however what is common within harmonising is not singing the same notes but rather its the different combination of notes that will produce consonance.

Consonance and Dissonance

Fig. 7 Frequency Integer Ratios (Harmonic Ratios)

Dissonance is defined as being the combination of multiple tones of different frequencies that result in the musically displeasing sound, whilst consonance is the combination of multiple tones of different frequencies that sound musically pleasing [7]. However, how do we perceive something as being dissonant or consonant? We know that our perception of hearing is subjective[7], so how can we perceive something as being pleasant or unpleasant?

Based on Greek scholar, Pythagoras, who explored this phenomenon of consonance and dissonance. What Pythagoras found about consonance from using a monochord was that it occurred "when the lengths or the frequencies of the two string segments are in a very special/unique integer ratios," [7] this can be seen from Fig. 7, in which the combination of notes (the grey) are considered dissonant.

Essentially, "perceived consonance comes from ratios involving adjacent, lower harmonics, whereas dissonance comes from ratios involving either higher or non-adjacent harmonics." [8]

"When the human ear perceives two pure-tone (single-harmonic) musical pitches that are sounded at the same time, the eardrum vibrates simultaneously at both frequencies. The brain perceives this as a pitch that is the fundamental of the harmonic series to which both of the sound pitches belong." [8] Moreover, when the frequencies of two pitches are very close together, an unpleasant ‘beating’ sensation occurs, which is perceived dissonance.

Helmholtz tried explaining dissonance stating that "If the frequencies are even closer together, less than a ‘just noticeable difference’ the beats are ‘washed out’." [8] "Complex musicals tones, which consist of a fundamental and higher harmonics, will sound dissonant if there are beats or a ‘roughness’ between higher harmonics." [8]

In conclusion, it is said that the musical tones with fundamentals that are related by small whole number ratios will have more coinciding higher harmonics and therefore less roughness, and be more consonant.[8]

See also

Human Voice

Harmonization

References

  1. ↑ 1.0 1.1 "Voice Acoustics: an introduction". UNSW Music Acoustics.
  2. ↑ 2.0 2.1 "VOICEBOX: THE PHYSICS AND EVOLUTION OF SPEECH" (PDF). Science Enhancement Program: 8. 2010.
  3. ↑ 3.0 3.1 3.2 "The Vocal Tract". VoiceScienceWorks.org.
  4. ↑ 4.0 4.1 4.2 "VOICEBOX: THE PHYSICS AND EVOLUTION OF SPEECH" (PDF). Science Enhancement Program: 9.
  5. ↑ 5.0 5.1 5.2 5.3 Science Buddies (December 4, 2014). "Singing Science: How High and Low Can You Go?". Scientific American.
  6. ↑ 6.0 6.1 HOW IT WORKS TEAM (December 5, 2018). "Singing science: Why do some people have better voices than others?". HOW IT WORKS.
  7. ↑ 7.0 7.1 7.2 Errede, Steven (2002). "Consonance & Dissonance" (PDF).
  8. ↑ 8.0 8.1 8.2 8.3 8.4 Lopresto, Michael (2009). "Experimenting with consonance and dissonance. Physics Education". Physics Education. 44: 145–150.
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