They like to listen to music and watch everything. What combines audio and video files? Their formats are different, the purpose also varies. But there is one concept that is common in these two cases. This parameter is called bitrate. What it is?
Basic information
To understand the essence of this concept, it is necessary to recall the basic methods of encoding and compressing sound. In Carlsbad, German scientists for the first time proposed an effective algorithm for compressing sound, which gave 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.
To do this, the sound is laid out on the Fourier harmonics. Guided by the results of research by physicians and biologists, all frequencies that the ear of the average person does not hear are thrown out of the series. For example, some quiet sounds are often removed against the background of a loud orchestra. In addition, unnecessarily long pauses between playbacks are cut to save space.
As a source of "raw materials" uses the standard format of digital sound WAV. It stores complete information about the original sound, being its digital cast. Digitization in this format occurs at a frequency of 44 kHz. It is WAV that uses archaic already audio CDs. Accordingly, during playback, the reverse transformation of the recorded information is simply done, as a result of which the music is obtained.
Record of auxiliary information
Information about the “cut off” harmonics is recorded in the created file, the size of which is much smaller than the original. Of course, its sound also has far from complete coincidence with the source material. But if the encoding was done carefully, then the human ear will not be able to feel the difference. Here we come back to the concept of bitrate. What is it?
Definition
This is the transmitted amount of data, and the transfer is associated with a specific time period. Thus, this concept directly reflects the amount of data that has been “ejected” from the source file. The lower the bitrate, the smaller the size of the resulting file, since almost all “extra” harmonics were removed from it.
They are measured in kilobits per second (Kbps), and for encoding sound in films they often use megabits per second (Mbps). If we talk about the classic MP3, then the most popular can be considered 128 kbps bitrate. What does it mean?
The fact is that this sampling frequency is the limit after which the sound starts to significantly deteriorate. Of course, it is not worth encoding performances of opera singers with its help, but this bitrate will encode pop div songs, not especially worsening the sound quality.
This difference is especially noticeable when listening to online radio on the Internet. Stations that use the 48kbps bit rate and the 128 kbps resource sound completely different.
What are they like?
There are two types: constants (CBR) and variables (VBR). This is especially significant 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, in this case there is no difference between dynamic and static data. If the value is variable, then less-dynamic scenes will be encoded using the minimum amount of resources.
A similar algorithm is used in standard compressed video formats . So, ordinary mpeg gives a significant gain in the size of the output file for the simple reason that every frame is analyzed and cut.
This principle is based on the fact that when scenes change slowly, the difference between frames is small, and therefore most of them can be greatly simplified by significantly reducing the size of the output file. With sharp frame changes, this will not work, and therefore you will have to use a higher bitrate. If you encode a movie or music using variable values, then it becomes impossible to predict the size of the output file: the computer can only give a very rough estimate.
Best value
You might have wondered which value would be most optimal. Let's try to answer this question.
We have already said that the lower limit is the mark of 128 kbps, but it is still undesirable to compress files to this size, since most of the useful information is lost. Most music lovers believe that the optimal bitrate is 192 kbps. Of course, in most cases, it is considered to be the optimal value of 320 kbps, but it no longer makes a significant difference.
It all depends on the hardware!
Of course, we won’t talk about the "warm tube sound", but with good acoustics you can quickly distinguish by ear files compressed with different quality. If the speakers can normally reproduce the entire range of high and low frequencies, then during playback a large number of artifacts appear, which indicate a lot of cut out harmonics.
Of course, on the dynamics of the cell phone of the first releases, there was no noticeable difference between 64 and 128 kbps, but modern mobile technology is made of much better components.
Choose the right values!
In general, you can compress a file perfectly if you imagine why and how you will use it. For example, if you want to compress a video game to make it a Portable version for playing with a flash drive, then for most of the game sounds the maximum bitrate will be 92 kbps. For voice prompts and exclamations, more is not necessary. On the contrary, when compressing classical music, saving is not worth the size, because otherwise you will lose the essence of the composition, since most of the finest nuances will be simply cut out.
However, in many cases, we can safely say that the best bitrate is 256 kbps. The vast majority of listeners will not perceive by ear any improvement with its further increase.
How to change the value?
Not so rarely, it may be necessary to change the bitrate. Just note that increasing the file size to 64 kbps, translating it into an audio-CD format, is stupid and pointless, since the cut-off harmonics will not be taken out of nowhere. But compressing a file with a lot of "weight", slightly cutting its characteristics, is quite acceptable.
Which bitrate program is best for use at home? Many users are probably familiar with the powerful Nero multimedia package, which also includes utilities for fully working with sound.
They have a familiar and fairly simple interface, intuitive, very high quality code music. However, buying a whole package (over 40 euros) for a couple of small applications is not too justified. Much better than Easy CD-DA Extractor. The program is paid, but there is a completely legal free version of it, which differs only in some limitations.
To change the bitrate with it, you need to open the main application window, double-clicking on its icon with the left mouse button, insert an audio CD into the drive, wait until a list of files on the disk appears in the dialog box. After that, you can press the RipCD button and indicate to the program the path to save the output files. All subsequent work will be continued in a fully automatic mode, any user involvement is not required.
That's what bitrate is for. What it is, you already know. If you choose its value consciously, it is quite possible to get a compressed sound, the quality of which will not noticeably suffer.