How Tone Relates to Harmonics and Sound Waves
When we hear the guitar sound, its vibration enters our ears. So, what is sound?
A sound is a type of vibration that enters our ears, besides, the frequency of a guitar sound should lie between 20 - 20 kHz to be audible or recognizable by our ears.
In acoustics, a tone is a sound that we can recognize by the regularity or continuity of its vibration.
A tone generally refers to a single frequency. However, the sound is a mixture of several frequencies, indeed sound is a mixture of tones.
On this page, we will understand the concept of tone and sound in detail.
What is Tone?
A tone is a musical or vocal or a melodious sound with reference to its pitch, quality, and strength/intensity. Thus a sound of single frequency is called tone; however, its intensity can vary.
Different Types of Voice Tones
Two different types of voice tones are as follows:
Simple tone
Complex tone
Firstly, a simple tone as we know is a single frequency sound whose intensity varies accordingly.
Secondly, a complex tone is a mixture of several simple tones, also known as overtones. Further, the tone of the lowest frequency is the fundamental overtone.
Additionally, the frequencies of the overtones can be whole multiples, i.e., 2nd, 3rd, 4th multiple.
Therefore, we call these fundamental frequencies, second, third, and fourth harmonics of the fundamental tone, itself known as the first harmonic.
Consequently, a combination of harmonic tones is pleasant to hear, and therefore, we call it a musical tone.
A tone is a single frequency sound, so now we will proceed further with the Physics of Sound.
The Physics of Sound
Assume the simple motion of a moving string. The instrument can be a violin, a guitar string, piano, sitar, or banjo string, which excites movement by plucking, striking/bowing it.
As a matter of fact, it makes no difference because the acoustic laws are the same for all instruments, no matter the type of principle they agree upon.
While looking at the below diagram, you might wonder how does the violin string move? And why is this sound considered musical?
Well! The answer to both questions is harmonics. Harmonics are different ways of movement of vibrations, happening simultaneously.
Indeed, harmonics are different ways of movement (inside the same body), occurring at the same time (instantly combining as a mathematical sum of the parts). The string moves similarly because, inside it, different types of movement occur at the same time.
Also, we hear a musical sound because all the vibrations are occurring simultaneously and give a beautiful sensation to our ears.
Therefore, the process through which various movements are happening at the same time inside one body is that of addition. The string of the violin vibrates at many of its resonant frequencies or harmonics simultaneously. By simply adding them, the resulting shape is that of a bowed string, as shown below:
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Point To Note:
The summing of all the parts or dotted vibration implies the simple (algebraic) addition of every point along the lines.
When all shapes are above the dotted, neutral line, they add up. However, when they are on the neutral line, their value is zero. If one or all of them are under the neutral line, they get subtracted.
Harmonic Motion
Harmonic motion is the occurrence of vibrations simultaneously. The term “harmonic” refers to the fundamental frequency of a waveform. Its types are:
First harmonic motion
Second harmonic motion
Third harmonic motion
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First Harmonic Motion
The first type of movement is the simple motion or the first harmonic motion.
All the sounds around you enter your ears as beautiful holographic bubbles, as you see in the image below:
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This simple up and down like a jump rope movement over the entire length of the string is the first harmonic motion.
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Second Harmonic Motion
The second type of movement of vibration splits the string into two identical though opposite parts, each oscillates in a fashion similar to the first harmonic.
When one of the halves of oscillation is up, the other is down, and vice-versa. This is what we call the second harmonic motion.
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In the second harmonic motion, we have two parts, i.e., node and antinode. So, let’s see what these are:
Nodes
The points that appear to be still standing (or do not undergo displacement) along with the medium are Nodes.
Antinodes
Particles that undergo maximum displacement between two points are antinodes. The nodes can be both positive and negative. The below figure illustrates nodes and antinodes:
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Third Harmonic Motion
In a third harmonic, we keep the node at both ends of a string so that the resulting wave pattern comprises four nodes and 3 antinodes.
It means that in a third harmonic motion, the waveform has a full sinusoidal wave cycle and one-half cycle. The diagram is as follows:
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Another term that we use in the Tone and Sound concept is a note. So, let’s understand this term:
What is a Note?
A mixture of several frequencies produces a sound that is pleasant to hear. This pleasant sound is called the note.
Point To Note:
An octave comprises eight different notes, its frequency ranges from 256 Hz to 512 Hz. This is how an octave looks like:
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FAQs on What Is Tone in Physics?
1. What is a tone in the context of Physics?
In Physics, a tone is defined as a sound that consists of a single, constant frequency. It is considered a pure sound because its waveform is a simple sine wave. For example, the sound produced by a tuning fork when struck correctly is a very close approximation of a pure tone. Most sounds we encounter in daily life are complex combinations of multiple tones.
2. What is the main difference between a tone and a note in sound?
The primary difference lies in their composition. A tone is a sound of a single frequency. A note, particularly in music, is a more complex sound that has a recognisable pitch. A note is typically composed of a fundamental frequency (which defines its pitch) along with several other frequencies called overtones or harmonics. So, a note is a mixture of several tones, giving it a rich quality or timbre.
3. What are the key characteristics that define the quality of a sound's tone?
The quality or timbre of a sound's tone is determined by three main characteristics:
- Pitch: Determined by the fundamental frequency of the sound wave. A higher frequency results in a higher pitch.
- Loudness: Determined by the amplitude of the sound wave. A larger amplitude results in a louder sound.
- Quality (or Timbre): Determined by the waveform, which is the combination of the fundamental frequency and the presence and intensity of its harmonics or overtones. This is why a flute and a violin playing the same note sound different.
4. If a pure tone is a single frequency, why do most sounds we hear seem so complex?
Most sounds we hear are complex because the objects producing them (like a guitar string, a drum skin, or human vocal cords) vibrate in multiple ways simultaneously. They vibrate at a fundamental frequency, which we perceive as the sound's pitch, but they also vibrate at integer multiples of that frequency, known as harmonics. Our ears and brain combine these different frequencies into a single, rich sound experience, which we perceive as the object's unique timbre, rather than a simple, pure tone.
5. How do harmonics and overtones create the specific 'tone' of a musical instrument?
Harmonics and overtones are crucial in defining an instrument's unique sonic identity or timbre. While the fundamental frequency determines the musical pitch (e.g., Middle C), the number and relative loudness of the accompanying harmonics create its characteristic quality. For instance, a clarinet produces strong odd-numbered harmonics, giving it a hollow sound, whereas a violin produces a rich spectrum of both even and odd harmonics, resulting in a fuller, brighter sound. This combination is what allows us to distinguish between different instruments playing the exact same note.
6. How is the concept of 'tone' applied in fields outside of music?
The concept of tone is vital in many technical fields. Here are a few examples:
- Acoustic Engineering: Engineers analyse the tonal components of noise to design effective soundproofing. By identifying the specific frequencies of unwanted sound (e.g., the drone of an engine), they can create materials that specifically absorb or cancel out those tones.
- Speech Synthesis: Creating realistic artificial voices requires precise manipulation of fundamental tones (for pitch and intonation) and overtones (formants) to mimic human speech patterns.
- Medical Diagnostics: Techniques like ultrasound imaging rely on sending high-frequency sound waves (tones) into the body and analysing the reflected waves to create images of internal organs.
