The MP3 audio compression method (also called MPEG-1 Layer 3) uses the properties of the human ear to save storage space. Frequencies inaudible to humans are filtered out of musical pieces. Depending on the degree of compression (so-called bit rates), this leads to no or severe loss of quality.
Music CDs use a constant bit rate (consumption of storage space / unit of time) of 1.4 Mbit per second for a stereo audio signal.
In comparison, a data rate of 192 kBit / s is sufficient with MP3 for almost CD quality music. It follows that the memory requirement is also significantly lower. There is about 10MB per minute of music on a music CD, good quality MP3 files only occupy about one eighth of this memory; So you can put around 8 hours of music on an MP3 CD.
A distinction is made between:
VBR – variable bit rate (variable bit rate)
With VBR, the bitrate constantly adapts to the music. Fewer bits are used in more “quiet” places (for example, few instruments or quiet passages), so the bit rate is lowered, while in more complex places the bit rate is increased as much as is necessary for the specified quality level is maintained at all times. Therefore, the MP3 file created in this way requires less storage space than MP3 files of comparable quality. The size of the final file is of course unpredictable and can vary greatly depending on the song and its genre. (is better than ABR and CBR)
ABR: average bit rate
ABR makes it possible to use variable bit rates but still meet the given average bit rate very precisely. In this way, the encoder saves bits in quiet places, which are then available to more complex places. The quality of this mode is between CBR and VBR, since the disadvantages of the CBR mode are eliminated, but the advantages of VBR mode only partially come into play, since the higher bit rates are used less frequently so as not to exceed the specified average bit rate. (is better than CBR)
CBR – constant bit rate
In “old-fashioned” CBR mode, a certain bit rate is used, regardless of what bit rate is actually required. As a result, higher bit rates are not available for complex locations, which is at the expense of quality, while bits are wasted in quiet locations, which is at the expense of file size.
Conclusion: the best method is VBR.
The only exception is the CBR bit rate (320 kbit / s), but this no longer makes sense.
other technical terms:
Joint Stereo
Joint stereo, also known as MS stereo, is a lossless encoding of the two audio channels. The great similarity of the channels is exploited by creating two new channels. The sum of the left and right channels is stored in the middle channel (M); the difference between the original channels is encoded in the side channel (S). Therefore, the middle channel contains most of the information, while in the side channel there is only a small amount of information available. Both channels are quantized separately and relatively good compression is achieved.
However, this trick does not work for songs with strong channel separation, that is, if the left and right are almost not similar. Logically mid / side stereo is also not possible with mono.
