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Bitrate - what is it? The best bitrates

Music and movies like to listen and watch everything. What unites audio and video files? Their formats are different, the purpose is also different. But there is one concept that is common in these two cases. This parameter is called bit rate. What it is?

Basic Information

To understand the essence of this concept, it is necessary to recall the main ways of encoding and compressing sound. In Carlsbad, German scientists first proposed an effective algorithm for sound compression, which gave the output files of quite acceptable quality. The essence of the method they proposed was that the source file was cut into fragments of 50 milliseconds, all of these fragments being further analyzed separately.

For this, the sound is decomposed into Fourier harmonics. Guided by the results of the research of physicians and biologists, out of a number all frequencies are ejected, which the ear of the average person does not hear. For example, they often take away some quiet sounds against the background of a loud orchestra. In addition, to save space, unnecessarily long pauses between playback are cut out.

As the initial "raw material" the standard format of digital sound WAV is used. It stores complete information about the original sound, being its digital impression. Digitization in this format occurs at a frequency of 44 kHz. It is WAV that uses archaic audio CDs. Accordingly, during playback, the reverse transformation of recorded information is simply done, resulting in music.

Recording of auxiliary information

The information about the "cut off" harmonics is recorded in the created file, the size of which is much smaller than the original one. Of course, its sound also has far from complete coincidence with the source material. But if the encoding was done carefully, the human ear will not be able to sense the difference. Here we come back to the concept of bitrate. What is it?

Definition

This is the transmitted amount of data, the transmission being related to a particular time interval. Thus, this concept directly reflects the amount of data that was "thrown out" from the source file. The smaller the bitrate, the smaller the size of the resulting file, since almost all the "extra" harmonics were removed from it.

They are measured in kilobits per second (Kbps), and for the encoding of sound in films, megabits per second (Mbps) are more often used. If we talk about the classic MP3, then the most popular is 128 kbps bitrate. What does it mean?

The fact is that this sampling frequency is the limit after which the sound begins to deteriorate noticeably. Of course, it's not worth to encode the performances of opera singers with it, but the songs of pop dives encode this bitrate, not particularly worsening the sound quality.

This difference is especially noticeable when listening to online radio on the Internet. Stations that use a bitrate of 48kbps and a resource of 128 kbps sound quite differently.

What are they like?

There are two types: constants (CBR) and variables (VBR). This is especially important when encoding video: if a constant bitrate was used, then the second of the movie will be compressed using a constant amount of data. Of course, there is no difference between dynamic and static data in this case. If the value is variable, then low dynamic scenes will be encoded using the minimum amount of resources.

A similar algorithm is used in standard compressed video formats . So, regular mpeg gives a significant gain in the size of the output file for the simple reason that each frame is analyzed and cropped.

This principle is based on the fact that with a slow change of scenes the difference between frames is small, and therefore most of them can be seriously simplified, greatly reducing the size of the output file. With sharp changes in the frame, this will not work, so you will have to use a higher bitrate. If you encode a movie or music using variable values, you can not predict the size of the output file: the computer can only give a very rough estimate.

The best values

You probably could ask yourself what value will be most optimal. Let's try to answer this question.

We have already said that the lower limit is a mark of 128 kbps, but compressing files to this size is still undesirable, since it loses most of the useful information. Most music lovers believe that the optimal bitrate is 192 kbps. Of course, in most cases it's considered to be optimal value of 320 kbps, but it does not give any significant difference.

It all depends on the equipment!

Of course, we will not talk about "warm tube sound", but on good acoustics you will quickly distinguish by ear files compressed with different quality. If the speakers can reproduce the full range of high and low frequencies, then a large number of artifacts appear, which indicate a set of cut out harmonics.

Of course, on the dynamics of the cell phone of the first issues, there was no difference between 64 and 128 kbps, but modern mobile technology is made from much better components.

Correctly choose the values!

In general, you can perfectly compress the file if you imagine what for and how you will apply it. For example, if you want to compress a video game to make a Portable version of it from a flash drive, then for most of the game sounds, the maximum bitrate will be 92 kbps. For voice prompts and exclamations of more and not necessary. On the contrary, when compressing classical music, you should not save money, because otherwise you will lose the very essence of the composition, since most of the subtlest nuances will simply be cut out.

However, in many cases it is possible to assume with confidence that the best bitrate is 256 kbps. The vast majority of listeners will not perceive by ear any improvement in its further increase.

How do I change the value?

It is not so rare that you may need to change the bitrate. Just note that increasing the file size in 64 kbps, translating it into the audio CD format, is silly and pointless, since the cut off harmonics are not taken anywhere. But a few compress the file with a large "weight", slightly reducing its characteristics, it is completely permissible.

What is the best bitrate program for home use? Many users are surely familiar with the powerful multimedia package Nero, which also includes utilities for full work with sound.

They have a familiar and fairly simple interface, are intuitive, they encode music very qualitatively. However, buying a whole package (more than 40 euros) for the sake of a couple of small applications is not too justified. Where is more convenient Easy CD-DA Extractor. The program is paid, but there is a completely legal free version of it, which differs only in certain restrictions.

To change the bitrate with it, you need to open the main application window by double-clicking on its icon with the left mouse button, insert it into the audio CD drive, wait until the list of files on the disk appears in the dialog box. After that, you can press the RipCD button and tell the program the path to save the output files. All subsequent work will continue in a fully automatic mode, no user interaction is required.

That's what bitrate is for. What it is, you already know. If you choose its value consciously, it is quite realistic to get a compressed sound, the quality of which is not significantly affected.

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