The FLAC format is more modern and with less loss of quality than MP3 but with a much larger file size, so MP3 remains one of the most widespread and used digital audio formats. With MP3 encoding at 320 kbps, excellent quality is achieved for most domestic digital audio players and for the human ear itself. But what is the difference between MP3 with a constant bit rate and a variable bit rate? Let’s clear the doubt.
Constant Bit Rate vs. variable bit rate
The variable bit rate coding method, known by the acronym VBR (Variable Bit Rate), is intended to achieve the highest audio quality evenly throughout the entire music track by performing an intelligent bit allocation during The coding process. That is, the Bit Rate varies to keep the audio quality as constant as possible throughout the file. In general, the MP3 encoding method with a variable bit rate produces a higher quality level than the constant bit rate coding for a similar Bitrate encoding.
Constant bit rate coding (CBR – Constant Bit Rate), meanwhile, is an encoding method that, instead of varying the bit rate, varies the audio quality to adjust to a fixed and constant bit rate at length of the MP3 file.
When to use a Constant Bit Rate?
If your priority is to get a certain MP3 file size, or at least a more or less predictable size, you should use a constant Bit Rate encoding.
When using a constant Bit Rate, the final file size is predictable although the quality of the MP3 audio will not be constant along the audio track.
When to use a Bit Rate Variable?
Bit Rate Variable encoding was developed for use when the main priority of MP3 encoding is a consistent quality throughout the track and the final file size is not the most important.
In an audio track some sections will be more difficult to code than others. Coding with Constant Bit Rate will encode the audio at the same Bit Rate set in advance, both in these more complex sections and in the easier sections. On the contrary, the coding with Bit Rate Variable will assign less bits in the easiest sections and will assign more bits when the section requires it because of its complexity. In this way, VBR encoding achieves a more uniform audio quality throughout the entire MP3 while the CBR achieves a constant Bit Rate.
In other words, if you use Constant Bit Rate the quality will be varied to reach the specified Bit Rate while using a Variable Bit Rate the Bit Rate is varied to achieve the highest possible and uniform quality.
All this does not mean that you don’t have to specify a Bit Rate for VBR encoding. Normally a fork will be specified, for example, 192-320 kbps, which means that a minimum of 192 kbps will be allocated for the easiest sections and up to a maximum of 320 kbps in the most complex sections of the music track.
The negative part is that MP3 encoding with Bit Rate Variable is not supported by some players. For me this disadvantage is part of the past and only if you try to play an MP3 in a really old player will not be able to read the file.
