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What is bitrate?


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What is bitrate?

Bitrate

Bitrate

Bitrate

Bit rate: the number of bits of information used to store or transfer one second of data transmission: video and / or audio recordings, including compressed ones.

Bit rate is expressed in bits per second (bit / s, bps), as well as derived values: kilo (kbps, kbps), mega (Mbps, Mbps), etc.

For streaming video and audio formats (such as MPEG and MP3) that use lossy compression]], the bit rate expresses the degree of compression of the stream. Most of the time, the video and audio bit rate is measured in megabits per second.

Increasing the bitrate provides a significant increase in video recording quality, which is especially noticeable when shooting dynamic scenes and small details.

Encoding modes
There are three compression modes for data transmission:

CBR (constant bit rate): with constant bit rate;
VBR (variable bit rate): with variable bit rate;
ABR (Average Bit Rate): with an average bit rate.

Constant bit rate
Constant Bit Rate, CBR – A variant of streaming data encoding, in which the required bit rate is initially set, which does not change throughout the file.

Its main advantage is the ability to predict the size of the final file fairly accurately.

However, the constant bitrate option is not very suitable for video or audio content, the dynamics of which change over time, as it does not provide an optimal size / quality ratio.

Variable bit rate
With a variable bit rate, the VBR codec selects the value of the bit rate based on the parameters (the level of the desired quality), and during the encoded segment, the bit rate may change.

This method provides the best quality / size ratio for the output file, but its exact size turns out to be very unpredictable. Depending on the nature of the sound (or image, in the case of video encoding), the size of the resulting file may differ several times.

Average bit rate
Average bit rate, ABR is a hybrid of constant and variable bit rates: the value in Mbps is set by the user and the program varies it within certain limits. However, unlike VBR, the codec is careful to use the maximum and minimum possible values, without risking going beyond the average specified by the user. This method allows the most flexible setting of the processing speed and with much higher precision (compared to VBR) in predicting the output file size.


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What is digital audio?

What is digital audio?

Digital Audio

Digital sound is nothing more than a combination of numbers.

DIGITAL AUDIO

With a certain algorithm, sound, such as air pressure, is converted into data streams and encoded for further processing and playback. Depending on the algorithm used, the music file has one format or another, one or another extension.

Remember that along with digital sound, there is analog sound, which is represented by a continuous electrical signal that reflects the change in the sound wave. The analog to digital sound conversion is a setting of the numerical value of the amplitude at a given time with a given density of values. Consequently, the more values ​​that are recorded, the more reliable and accurate the image of the digitized sound fragment is recreated. With such digitization, very voluminous data matrices emerge that, depending on the format used, differ in the sound quality / volume ratio of the final file.

Perhaps the main advantage of digital audio over analog is the ability to store and copy data indefinitely without losing the original quality (whereas when copying from one analog medium to another, a decrease in recording quality is quite noticeable).

The most widespread and popular digital audio format today is MP3 (MPEG Layer 3). It was developed, after a series of intermediate formats and investigations, started in 1987, by the Fraunhofer Institute in Germany.

The developers of the format were faced with the task of simplifying and reducing the cost of shipping long musical fragments. As you know, one minute of a stereo signal from a CD (16 bit, 44.1 kHz sample rate) takes up about ten megabytes of memory. At the same time, unlike text or graphic files, the audio signal cannot be compressed without loss of quality. Thus, modem transmission of an uncompressed composition from an audio CD lasting 3 minutes at a data transfer rate of, say, 24 kbps will take several hours. Scientists at the Fraunhofer Institute managed to achieve multiple file size compression: on average, one minute of a compressed audio signal in MP3 format takes about 1 megabyte. The principle of compression is based on the removal of “unnecessary” sounds from the music file, to which the human ear is immune, or which duplicate each other.

The main factor that determines the relationship between file size and sound quality within a given format is the bit rate. Bit rate is an indicator of how much information a second of sound encodes. The higher it is, the less distortion and the closer the encoded composition is to the original. The most common on the Internet are compositions with 128 and 192 Kbps bitrates. The maximum bitrate supported by programs and devices that work with MP3 is 320 Kbps. In practice, only an expert or a professional who works with sound can notice the differences between an MP3 file with a 320 bit rate.

To optimize the size of MP3 music files while maintaining decent quality, a variable bit rate (abbreviation VBR – variable bit rate) is used. In this case, the encoding program divides the file into fragments of different spectral saturation and encodes them with a suitable bit rate. Most modern MP3 players support variable bit rate playback. A significant advantage of MP3 files is that they can contain the name of the artist, the name of the track and the album, the year of its release, etc. The set of this data is called ID3 tags. Most modern gamers can read and display them on the screen.

In 2001, Swedish Coding Technologies and Thomson Multimedia developed the MP3 Pro codec. It is MP3-based and as a result is fully MP3 backward compatible and only partially forward compatible. It uses SBR (Spectral Band Replication) technology, so the codec provides good quality at low bit rates. However, the encoding quality at medium to high bit rates is inferior to that of most other codecs. For this reason, this format is mainly used for broadcasts on the Internet and demonstrations of fragments of new musical compositions.

Another type of MP3 was the development of MP3 Surround, recently introduced by the creators of MP3: the Fraunhofer Institute. This format repeats all the characteristics of multi-channel sound, while still being compatible with standard stereo MP3: information describing the spatial characteristics of the sound is recorded on an additional track. By playing files of this format on special equipment capable of reading this track, you can obtain surround sound that conforms to the Surround 5.1 standard.

Audio. Digital and analog audio

Audio. Digital and analog audio

Digital Audio

Despite the fact that most of the external information we acquire with the help of sight, sound images are no less important to us and often even more. Try watching a movie with the sound turned off; in 2-3 minutes you will lose the thread of the plot and interest in what is happening, no matter how large the screen and the high quality image. Thus, a pianist played off-screen in silent movies. If you remove the picture and leave the sound, the movie can be “heard” like a fascinating radio show.

DIGITAL AUDIO

Hearing gives us information about what we do not see, since the visual perception sector is limited and the ear captures sounds from all directions, complementing visual images.

Hearing gives us information about what we do not see, since the sector of visual perception is limited and the ear captures the sounds that come from everywhere, complementing the visual images. At the same time, our hearing with great precision can locate an invisible sound source in direction, distance, speed of movement.

They learned to convert sound into electrical vibrations long before images. This was preceded by a mechanical recording of sound vibrations, whose history dates back to the 19th century.

Accelerated progress, including the ability to transmit sound at a distance, was made possible by electricity, with the advent of amplifying, acoustic, and electro-acoustic equipment and transducers – microphones, pickups, dynamic heads, and other emitters. Today, audio signals are transmitted not only over cables and over the air, but also over fiber optic communication lines, primarily in digital form.

The acoustic vibrations are converted into an electrical signal, usually by microphones. Any microphone contains a moving element, the vibrations of which generate a current or voltage in a certain way. The most common type of microphone is the dynamic, which is a reverse speaker. The vibrations of the air set in motion a membrane that is rigidly connected to a moving coil in a magnetic field. A condenser microphone, in fact, is a condenser, one of whose plates vibrates at the same time as the sound, and with it the capacitance between the plates changes. Ribbon microphones use the same principle, only one of the plates is freely suspended. Similar to a condenser electret microphone, whose plates, in the process of oscillation, generate by themselves an electric charge proportional to the amplitude of the oscillations. Many models of microphones have a built-in amplifier (the signal level directly from the acoustic-electric transducer is very low). Unlike a microphone, the pickup of an electric musical instrument registers vibrations not from the air, but from a solid body: a string or the soundboard of an instrument. The cartridge reads the record slot using a needle mechanically connected to moving coils in a magnetic field, or magnets if the coils are stationary. Or the vibrations of the needle are transmitted to the piezoelectric element which, under mechanical stress, generates an electrical charge. In magnetic recording, an audio signal is recorded on a magnetic tape and then read with a special head. Finally, optical recording was traditionally adopted in cinematography: an opaque soundtrack was applied from the edge of the film,

In synthesizers, sound is born directly in the form of electrical vibrations, there is no primary transformation of acoustic waves into an electrical signal.

Modern autumn sound sources are diverse and digital media are becoming more and more common: CDs, DVDs, although vinyl records are also preserved. We continue to listen to radio, both terrestrial and via cable (radio hotspots). Sound accompanies television shows and movies, not to mention a phenomenon as familiar as telephony. A computer receives an increasing share in the world of audio, allowing it to conveniently archive, combine and process sound programs in the form of files. In the digital age, digitized speech and music are transmitted through digital channels, including the Internet, without serious losses in transportation. This is provided by digital encoding and the loss is due solely to compression, which is used most often. However, in digital media, either it does not exist at all (CD, SACD), or lossless audio compression algorithms are used (DVD Audio, DVD Video). In other cases, the degree of compression is determined by the required level of soundtrack quality (MP3 files, digital telephony, digital television, some types of media).