Sound information on the computer
Sound is a continuous signal, a sound wave with variable amplitude and frequency.
The greater the amplitude of the signal, the stronger it will be for a person.
The higher the frequency of the signal, the higher the pitch.
The frequency of a sound wave is expressed as a number of vibrations per second and is measured in Hertz (Hz, Hz).
The human ear can perceive sounds in the range of Hz to 20 kHz, which is called sound .2020
The number of bits per audio signal is called the audio coding depth.
Modern sound cards provide 16-, 32-, or 64-bit audio encoding depth. 163264
When encoding audio information, a continuous signal is replaced by a discrete one, that is, it is converted into a sequence of electrical impulses (binary zeros and ones).
The process of converting audio signals from a continuous representation form to a discrete digital form is called digitization.
An important characteristic when encoding audio is the sample rate, the number of signal level measurements in second: 1
– (one) measurement per second corresponds to a frequency of Hz; 11
– measurements per second correspond to a frequency of kHz. 10001
Audio sample rate is the number of audio volume measurements in one second.
The number of measurements can be in the range of kHz to kHz (from the radio transmission frequency to the frequency corresponding to the sound quality of musical media) .848
The higher the sampling frequency and depth of the sound, the better the sound of the digitized sound. The lowest quality of digitized sound, corresponding to the quality of telephone communication, is obtained at a sampling rate of times per second, a sampling rate of bits, and by recording an audio track (“mono” mode). The highest quality digitized audio, corresponding to the quality of an audio CD, is achieved with a sampling rate of times per second, a sampling rate of bits, and the recording of two audio tracks (stereo mode) .8000 848 000 16
It should be remembered that the higher the quality of the digital sound, the greater the volume of information in the audio file.
The volume of information in a mono audio file () can be estimated as follows: VV = N⋅ f⋅ k, where is the total duration of the sound (seconds), is the sampling frequency (Hz), is the encoding depth (bit) .norteFk
For example, with a sound duration of one minute and a medium sound quality (bits, kHz): 11624
V = 60 ⋅ 24000 ⋅ 16 bits = 23040000 bits = 2,880,000 bytes = 2812.5 kB = 2.75 MB.
When encoding stereo sound, the sampling process is performed separately and independently for the left and right channels, consequently doubling the size of the audio file compared to mono sound.
For example, let’s estimate the information volume of a digital stereo sound file with a duration of one second with an average sound quality (bits, measurements per second). For this encoding, the depth must be multiplied by the number of measurements per second and multiplied by (stereo): 11624 00012
V = 16 bits ⋅ 24000⋅2 = 768000 bits = 96000 bytes = 93.75 KB.
There are several methods for encoding audio information with binary code, among which two main areas can be distinguished: the FM method and the Wave-Table method.
The FM (Frequency Modulation) method is based on the fact that, theoretically, any complex sound can be decomposed into a sequence of the simplest harmonic signals of different frequencies, each of which is a regular sinusoid and therefore It can be described by a code. The decomposition of audio signals into harmonic series and representation in the form of discrete digital signals is done by special devices – analog-to-digital converters (ADC).
Conversion of an audio signal into a discrete signal: to – audio signal at the ADC input; b – discrete signal at the ADC output.
Digital-to-analog converters (DACs) perform reverse conversion to reproduce sound encoded with a numeric code. The sound conversion process is shown in Fig. Below. This encoding method does not provide good sound quality, but it does provide compact code.
Conversion of a discrete signal into an audio signal: to – discrete signal at the DAC input; b – audio signal at the DAC output.
The table wave method (the Wave, the Table) is based on the fact that the previously prepared tables store sound samples from the world, musical instruments, etc.
