Natural Sound

To understand the characteristics of digital sound, first make a short introduction to the characteristics of sound and its most basic concepts.

The sound is vibration of air particles that propagate through the air, thanks to the particles of air moving, the vibrations reach our ears. The hearing in humans, occurs whenever vibrations have a frequency between about 15 and 20,000 hertz, and its intensity is enough to reach the inner ear. When the vibrations move these margins are speaking of ultrasound and are invisible to humans.

The sound characteristics can be measured and it is used for units of hertz (Hz) measuring the frequency of a sound or vibration is many times a second, and the decibel (dB) that measures the intensity (amplitude) of a wave.

Sample of four sounds with different frequencies

Shows the same sound at three different intensities

Computer and Sounds

The digital word indicates the presence of numerical processes to realize a fact (image, sound, etc.) Digital audio systems have circuitry to keep track of music, in a nutshell what these circuits is to record a long string of numbers (scanning or sampling) with a device called an analog digital converter (ADC), which is responsible for monitoring the evolution of the wave and assign each time a numeric value, then this numerical value is decoded by a converter called digital -analog (DAC).

 

Digital Sound Quality

Sound quality depends on the sampling frequency and resolution.

Frequency of sampling or sampling, refers to the number of measurements that are made per second. The greater the number of samples the better the sound quality, for example if the sampling rate is one per second the sound variations that occur in the interim will not be registered. According to studies, the sampling frequency should be twice the highest sound can be heard, as the human ear can hear up to about 20,000 Hertz, the optimal sampling frequency is 44.1 kHz. (44,100 hertz), the frequency used in music CDs. As the instruments or human voices fail the frequency of 10 kHz., With a sampling frequency of 32 kHz. is more than sufficient, lowering the sampling frequency much the sound becomes dull or sharp as some frequencies are lost.

The resolution, the term refers to the accuracy of the measured frequency. It is measured in bits, if the resolution is 8 bits have 256 possible levels (2 ^ 8 = 256). Extending a 16 bit range extends to 65,535 (2 ^ 16 = 65536). As a reference we can say that a CD is recorded at 44.1 Khz. and a resolution of 16 bits.

If you want to scan 3 minutes of music at a sampling rate of 44.1 Khz. and storing each sample by two bytes (16 bits) yields the following:

3 min x 60 sec / min

x 44,100 samples / sec

x 2 bytes / sample

---------------------------

15,876,000 bytes

The above calculation shows that to store a three-minute song with professional quality needs approximately 16 MB. This is where the problem arises because, although the hard drives or other storage media has grown much, having several songs would occupy much of the disk of the computer, To solve this problem have been developed file formats that allow for sound recordings very good quality using a compression method, the problem is that sound can be edited to be modified.

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