Sound quality

Information Processing > Sound quality

Sound Quality is the quality of the Audio. The Bandwidth of the Sound (in Hertz) that the Electronic Device Sampling the Sound Signals affects Sound Quality. Humans can hear vibrations ranging from about 20 Hz to approximately 20 kHz. Table 1 shows the various Sampling Rates and their Applications.

Sampling Rates Applications
8,000 Hz Telephone Quality
11,025 Hz Low-end Radio Quality (good for voice)
22,050 Hz Radio Quality (good for music and voice)
44,100 Hz CD Quality (high quality)

Table 1: The various Sampling Rates and their applications

What is Attenuation?

Attenuation means loss in power of a signal, and is sometimes called "loss". Attenuation always happens when signals travel over long distances. Attenuation is measure in decibels (dB).

Attenuation in conventional fiber optic cables is specified as the number of decibels lost per foot, or per 1,000 feet, or per kilometer, or per mile. The more efficient cables have less attenuation.

To transmit signals over long distances, repeaters (amplifiers) can be used along the length of a cable. The repeaters boost the signal strength to overcome attenuation.

What are Decibels?

The decibel (dB) is a logarithmic unit used to describe a ratio. It is used in a wide variety of measurements in Acoustics, Physics and Electronics.

In Acoustics, Sound is usually measured with Microphones and they respond (approximately) proportionally to the Sound Pressure, p. As the human ear is capable of hearing a very large range of sounds, logarithmic units are useful to deal with such a large range. Psychologists also say that our sense of hearing is roughly logarithmic.

The decibel (dB) is a logarithmic unit that often used to quantify Sound Pressure Levels (SPL) relative to some 0 dB reference. SPL can be expressed in decibels with the following formula:

PdB = 20 log10(p1 / p0)

where p0 = 2x10-5 Pa is the reference Sound Pressure, which is roughly the Threshold of Hearing.

In the following, different Sound Sources and their corresponding SPLs are presented:

0 dB Threshold of hearing
40 dB Sound level in a quiet home
60 dB Normal conversation
100 dB Heavy truck at 1 m
120 dB Rock concert, inside disco
130 dB Jet aircraft taking off at 100 m
140 dB Gunshot

SPLs above 85 dB are considered harmful, while 120 dB is unsafe and 150 dB causes physical damage to the human body.

What is Timbre?

Sound is generally characterized by pitch, loudness, and quality. Timbre, or quality, describes those sound characteristics which allows the ear to distinguish sounds with the same pitch and loudness.

Voices and musical instruments sound different because they have different timbres. Timbre depends on the waveform of the sound. Smooth waveforms give soft timbres, and sharp, pointed waveforms give harsh timbres. A classical guitar has a soft timbre and a cymbal has a harsh timbre.

Information Processing > Sound quality