History of digital audio
By its nature, sound is an oscillatory movement of particles in an elastic medium that propagates in the form of waves. After it became clear that sound represents such vibrations, the idea came up of recording them by repeating the shape on solid material.
So, in 1877, Thomas Edison created a phonograph, a device for the mechanical recording and reproduction of sound. And in 1888, the German E. Berliner invented the gramophone – the era of gramophone records began, which became the first massive carriers of audio information.
Thomas Edison and his phonograph
FIG. Inventor Thomas Edison and His Record Making: The Phonograph
Having studied the laws of electromagnetism, man made successful experiments to convert sound waves into electromagnetic waves and preserve them. This is how magnetic tape appeared, which became widespread in the middle of the 20th century.
For digital technology to store, process, and reproduce sound, it is converted to digital format by an analog-to-digital converter (ADC), which converts an analog signal into a sequence of numbers. This is called Pulse Code Modulation (PCM).
It happens like this: the ADC measures the amplitude of an analog signal many times per second and outputs the results in the form of numbers. However, the measurement result does not exactly match a continuous electrical signal: it depends on the number of measurements and their precision.
The frequency at which the measurements are taken is called the sample rate, and the precision of the amplitude measurements indicates the number of bits used to indicate the result of the measurement. This parameter is called the bit depth. For example, if the sampling frequency is 44.1 kHz, this means that the signal is measured 44 100 times in one second.
For the analog signal to be accurately reconstructed from its samples, the sample rate must be twice the maximum audio frequency. That is, if the analog signal contains frequency components from 0 Hz to 20 Hz, then the frequency of its sampling must be at least 40 kHz.
Digital audio formats
Of course, for digitized sound to be stored, transmitted, and converted, there must be certain digital sound standards – audio formats. Today, there are many such formats, each of which uses its own sound processing algorithm. They also differ in the information carriers.
The most popular and widespread in the field of home use today are ordinary music CDs – CDs. There are also relatively new recording formats, Super Audio Compact Disk (SACD) and DVD-Audio (or simply DVD-A). In addition, formats that use digital data compression have become widespread.
The most popular among them is MPEG-1/2 / 2.5 Layer 3 (MP3). Microsoft also did not stay away from the sound industry, as it developed its own compression algorithm, WMA, which is also actively promoted in the market.
New audio file formats appear every year, but no player on the market supports the playback of all formats.
In fact, the term MP3 player is only correct for players that support the MP3 format. Let’s see what’s what in audio formats.
Before looking at the various audio file formats (codecs), let’s take a look at a few terms.
Bitrate
Bit rate is the space required for 1 second of music. With a bit rate of 128 kbps (kilobits per second) = 16 kbps (kilobytes per second), approximately 5 megabytes are needed for 5 minutes of music.
The higher the bit rate, the higher the quality of the music. But this as long as the bit rate of the original format is higher than the bit rate of the encoded format. By compressing a CD to MP3 at 320 kbps, you get better sound quality than 128 kbps, but converting from 128 kbps to 320 kbps will not improve the quality and may even degrade it.
Often times a 128kbps bit rate masquerades as CD quality, but this is not actually the case. If you have enough high-quality equipment, you will hear it immediately. Manufacturers like to give an estimate of the number of songs that go into a player at a very low bit rate, and many consumers are unaware that audio files vary in size. Therefore, you should not rely on the numbers in the advertisements, in fact, much less the songs in your collection can fit in the player.
Compression
Uncompressed audio takes up a lot of space. To reduce the size of audio files in formats such as MP3, programs cut off the part of the frequency range that the human ear cannot hear.
