Sound file resolution. Audio encoding and processing
Basic concepts
The sampling frequency (f) determines the number of samples stored in 1 second;
1 Hz (one hertz) is one count per second,
and 8 kHz is 8000 samples per second
The encoding depth (b) is the number of bits required to encode the level of
Memory capacity for data storage 1 channel (mono)
(to store information about a sound with a duration of t seconds, encoded with a sampling rate of f Hz and a encoding depth of b bits, 1 bit of memory is required)
For 2-channel (stereo) recording, the amount of memory required to store data for one channel is multiplied by 2
I = f b t 2
Units of measurement I – bits, b – bits, f – Hertz, t – seconds Sampling frequency 44.1 kHz, 22.05 kHz, 11.025 kHz
Audio encoding
Basic theoretical provisions
Sound time sampling. In order for a computer to process sound, a continuous audio signal must be converted to a discrete digital form using time sampling. A continuous sound wave is divided into separate small time sections, for each section a certain value of sound intensity is set.
Therefore, the continuous dependence of the loudness of the sound at time A (t) is replaced by a discrete sequence of loudness levels. On the graph, this appears to replace a smooth curve with a sequence of “steps.”
Sampling frequency. A microphone connected to the sound card is used to record analog audio and convert it to digital format. The quality of the digital sound obtained depends on the number of measurements of the sound volume level per unit time, that is, sampling rate. The more measurements are made in 1 second (the higher the sampling frequency), the more accurately the “ladder” of the digital audio signal repeats the curve of the analog signal.
Audio sample rate is the number of measurements of the volume of a sound per second, measured in Hertz (Hz). Let us denote the sampling frequency with the letter f.
The audio sample rate can vary between 8000 and 48000 sound volume measurements per second. One of three frequencies is selected for encoding: 44.1 KHz, 22.05 KHz, 11.025 KHz.
Audio encoding depth. Each “step” is assigned a specific value for the sound volume level. Loudness levels can be seen as a set of possible states N, for which encoding a certain amount of information b is required, which is called the audio encoding depth.
Audio encoding depth is the amount of information required to encode the discrete volume levels of digital audio.
If the encoding depth is known, then the number of digital audio loudness levels can be calculated using the formula N = 2b. Let the audio encoding depth be 16 bit, then the number of sound volume levels is:
N = 2 b = 2 16 = 65 536.
During the encoding process, each sound volume level is assigned its own 16-bit binary code, the lowest sound level will correspond to the code 0000000000000000 and the highest – 1111111111111111.
The quality of digitized sound. 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 8000 times per second, a sampling rate of 8 bits, and by recording an audio track (“mono” mode). The highest quality of digitized sound, corresponding to the quality of an audio CD, is achieved with a sampling rate of 48,000 times per second, a sampling rate of 16 bits and the recording of two audio tracks (stereo mode) .
