What is Quality of Sound?

A sound or a sound wave is defined as the energy produced due to the vibrations of particles in a medium. When any medium produces a disturbance or vibrations, it causes a movement in the air particles which produces sound waves. Molecules in the air vibrate about a certain average position and create compressions and rarefactions. This is called pitch which is defined as the frequency of sound. The frequency is defined as the number of oscillations in pressure per second.

The particles vibrating in longitudinal waves propagate along the direction of the wave since they rely on the pressure forces.  The term elasticity is the ability of a solid-state matter to return to its original; shape due to external forces. The speed of sound depends on the elasticity of the medium, where it is directly proportional. For a sound to be loud it must have high amplitude. This amplitude increases with the energy of the sound. The intensity of the sound is directly proportional to the square of the amplitude of the sound wave and its SI unit is in decibels (dB). Sound travels at 340 m/s. The sound quality is good when the sounds reach our ears with the same intensity, pitch, quality, and loudness. A good sound system should produce good sound quality by adjusting these factors.

Reverberation is a term defined as when the sound waves get interrupted by an obstacle, so when this sound reaches our ear, it will sound different from the original audio. Example: Echo.

Explanation

When a sound is produced, it proposes in air and reaches our eardrum, this wave vibrates and sends a signal to our brain. Every human's hearing frequency range is between 20 Hz to 20kHz. Above 20kHz is ultrasonic sound and below 20kHz is infrasonic sound.

The audio quality or sound quality depends on Intensity, duration of time, timbre, and frequency. The duration of the sound depends on the persistence of the sound waves., the higher the persistence, the longer we hear the sound. The timbre is the combination of qualities that differentiates from other sounds of the same pitch and volume. It depends on the fundamental sound and the harmonic content of the other sound. The harmonic contents are the number and relative intensity of the harmonics present in the sound. Most of the sounds have harmonic frequencies and the rest are pure forms of sounds. These harmonics consist of fundamental frequencies and a series of overtone frequencies.

There are three contributors to time: 

1. Attack and Decay
2. Harmonic content
3. The Vibrato

1. Attack and Decay: It tells the ability of the amplitude of the sound to reach its maximum at the fastest rate and after it reaches the maximum point, the ability of the amplitude to become zero at the faster rate.

2. Harmonic content: The most important component of timbre for sustained tones. When they are super positioned, they create a new waveform. It switches from time plot to frequency plot making it more event. The amplitudes of the individual harmonics can be determined by calculation of Fourier analysis and showcased as a frequency function.

3. The vibrato or tremolo is a periodic change in the pitch of the tone and tremolo indicated the periodic change in the amplitude and loudness of the tone. Hence the vibrato is the Frequency modulator and tremolo is the Amplitude moderator. 

Noise is a peculiar form of sound where it is unpleasant and disturbing for the human ears. It may be caused due to the imbalance of intensity, pitch, and timbre where it enters our hearing system and these fluctuated signals reach our brain making us feel uncomfortable. It carries a negative connotation. 

Noise reduction is a method to eliminate noise with the help of destructive interference. 

An earphone or headphone is an output electronic device that allows us to listen to audio without spreading the sound from a confined range. There are several types of earphones like wired and wireless, built in-ear and on the head types. The wireless earphones or earbuds use Bluetooth connectivity as their input signal to produce audio. Certain headphones are also made of noise-canceling features. Noise cancellation means the headphone reduces unwanted ambient sounds using active noise control. It controls the loudness of the sound and makes it fully impactful for our listening. 

The frequency response is the capacity and measure of the range of frequencies and tones a device can produce. It decides the sound quality and the audibility. The ideal frequency of the component must be equal to the audio input. This term is called the flat frequency response where a standard sine wave has the same amplitude throughout all the frequency even at the output so the sound level would be even.

Other Important Terminologies

Sound pressure: It is the average variation in the atmospheric pressure caused by the sound. Its reference level is about 2×10^-5 N/m²

Sound power:  It is defined as the rate at which the sound energy is emitted, transmitted, and received per unit time. Sound power is often referred to as acoustic power level. The sound power level is determined by the source producing a sound pressure level at a certain distance. The acoustic power level is about 10^-12 Watts.

Doppler effect

It is the change in frequency when there is a relative motion between the source of the waves and the observer of waves. The Doppler shift is known as the change in frequency of sound due to the relative motion of either the source or the receiver.

Audiophile: A person who reproduces high-fidelity sound and is responsible of finding or recording high quality sounds.

Supersonic and Subsonic

Subsonic is a term used when the sound waves are slower than the actual speed of sound 340 m/s. Supersonic is a term used when the sound waves travel faster than the speed of sound 340 m/s. The shock waves are supersonic sounds.

Dynamic range

It is defined as the sound waves with high intensity per the sound waves to a low intensity that can be transmitted or reproduced by a sound system. 

Speech intelligibility: It is a term to describe how clear and refined a person's speech is comprehensible to the listener. For this, the person has to produce a good quality of sound.

Conclusion

Therefore, for a good quality of sound is when there is low distortion, uninhibited dynamic range and appropriate frequency.  A good sound quality is beneficial for a good listener. 

Context and Applications   

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for 

• Bachelors in Science Physics 
• Masters in Science Physics