Loudness, Pitch and Quality of Sound for JEE

We all probably know what sound is; it could be the sound of the fan, the sound of horns, or anything in general that we can hear. In Physics, sound is defined as a vibration that travels through a transmission medium, such as a gas, liquid, or solid, as an acoustic wave. We’ll learn more about the frequency of sound waves in this article but for now, we will state that only acoustic waves with frequencies between roughly 20 Hz and 20 kHz, or the audio frequency range, can cause a human to have an auditory sensation. These are sound waves with wavelengths ranging from 17 metres to 1.7 millimetres in the air at atmospheric pressure. 

The sounds above 20KHz and below 20Hz are not audible to humans. The sound waves above 20KHz are known as ultrasound and the sound waves below 20 Hz are known as infrasound waves. The range of sound waves that an animal can perceive varies from animal to animal. The range that we have stated above is only for humans.

Characteristics of Sound

The sound that we hear is the result of sound waves. Our brain then perceives these waves and that’s how we listen to anything. There are some characteristics of sound waves that make sounds from different sources differ from one another. 

Five main characteristics of sound waves can be listed. They are:

1. Wavelength

The wavelength of sound waves may be its most significant feature. When a sound wave travels through a certain medium, it undergoes compressions and rarefactions. The wavelength is the distance a wave travels before repeating itself. It is the distance between the centres of two subsequent rarefactions or compressions, or it is the sum of the lengths of the neighbouring compression and rarefaction. Sound waves are also known as compression waves. 

2. Amplitude

The magnitude of a particular wave is its amplitude. Consider it as being more like the wave's height than its length. The maximum movement of the particles the sound wave disturbs as it travels through a medium is a better way to quantify amplitude in the case of sound waves because they are longitudinal waves. 

High amplitude sound waves have more energy. The amount of compression and expansion a sound wave experiences as it travels through a medium is referred to as the amplitude of the sound. Our ears interpret this amplitude as loudness. Loud sounds are equivalent to high amplitude.

3. Frequency

The frequency is the number of sound waves produced by a sound per second. A high-frequency sound has more waves than a low-frequency sound, which has the opposite. Sound frequency is expressed in hertz (HZ) and is independent of the medium through which the sound is travelling. Pitch is another name for frequency in sound.

4. Time Period

The time period is just the reciprocal of the frequency of a sound wave. It is defined as the time taken for the sound wave to complete one vibration in the density of the medium through which it is travelling. The SI unit of the time period is seconds.

5. Speed 

A basic characteristic of the material is the speed of sound, which is dependent on the medium through which the waves travel.

Pitch of a Sound 

As we have already mentioned before, the pitch of a sound wave is basically just the frequency of that particular sound wave. We all must be familiar with the terms high pitch and low pitch. We can distinguish notes using the concept of pitch. Likewise, we can identify the female and male voices just by listening to them due to the knowledge of pitch. Female voices have a high pitch and male voices have a comparatively low pitch. A high pitch refers to a sound wave that has a high frequency. Similarly, a low-pitched voice has a low frequency. Shrill is a term used to describe a high-frequency sound.

For instance, a small infant's voice has a greater frequency when speaking. So, when a baby speaks, the pitch is higher than that of a man. A small infant’s voice is an example of high-pitched sound. 

Loudness of a Sound 

The sense of loudness is related to the strength of the localised sound wave. We have already mentioned before that the amplitude is related to the loudness of a sound wave. A loud sound has a high amplitude. Amplitude is also related to the energy of the sound wave and this means that a loud wave has high energy. You must’ve heard your parents say that a loud sound can damage your ears, and the reason is that loud sounds have high energy which is not good for our ears. 

Let's imagine that when we pluck a sitar string, it initially vibrates with a low amplitude. If we exert more force by plucking harder, the string will vibrate with higher amplitude and make a louder sound. Sound intensity grows along with vibration amplitude.

Since we mentioned that a loud sound has high energy, this means that there should be some relation between the loudness and intensity of the sound wave. The loudness is measured in decibels (dB) and it is a dimensionless quantity. The relation between the intensity of the sound wave and the loudness is given as

L=log(I)

Here, L is the loudness and I is the intensity of the sound wave. 

Intensity is also related to the amplitude of the sound wave which should be obvious now. The intensity and amplitude relation is that the intensity is proportional to the square of the amplitude. 

Very often than not, pitch and loudness are used synonymously, but they are different concepts. The difference between loudness and pitch is that pitch is our ears' response to a sound's frequency, while loudness is influenced by wave energy and amplitude. Generally speaking, the pitch is what gives each person's voice its unique sound.

Difference Between Pitch and Loudness

Quality of a Sound

The quality of a sound is also known as the timbre of the sound. Timbre refers to the quality of many sounds, such as the thud of falling rock, the buzz of a drill, the tone of an instrument, or the timbre of a voice, and it denotes the pre-conscious assignment of a sonic identity to a sound. 

The timbre aids us in differentiating various sources because they all make different sounds. It is enjoyable to listen to high-quality sound. The varying sizes, shapes, and loudness harmonics of the instruments allow for easy differentiation of their sounds.

Conclusion

Like electricity, heat, or light, the sound is a kind of energy. Wavelength, amplitude, frequency, time period, and velocity are the five main characteristics of sound waves. Pitch refers to the apparent "lowness" or "peak" of a sound and symbolises the cyclical, repeated nature of the sound-generating vibrations. The pitch of a sound wave is related to the frequency of the sound wave. The loudness is related to the amplitude of a sound wave. High amplitude sound waves are loud and have high energy. The quality of a sound is also known as the Timbre of the sound.