The relationship between frequency and bit rate, and the sound quality of MP3 Part 5
The above is the fixed code rate compression ratio.
In lame, this is called CBR (ie non-variable code rate). In fact, the most important feature of lame is that it provides users with a VBR variable code rate compression method. This method is a very good encoding method in some pauses, and the simple signal will automatically reduce the bitrate and reduce the file size. However, how to choose the lowest and highest VBR bitrate range to get the most appropriate file and sound quality? This is another problem that needs to be solved through experimentation. Considering 128kbps as the base value, we choose 96kbps to 160kbps as the compression range. The compressed file size is 3801kb which is just over 128kbps CBR. 387 kb, but the sound is definitely improved by a great deal. First, the high-frequency distortion is at least half as small. Although there is still a lot of noise in the details, the first listening sensation is much stronger than 128 kbps. The average code after compression speed is 147 kbps, which is also very space efficient. Then experiment with 96kbps to 192kbps, 96kbps to 224kbps, 96kbps to 256kbps, 96kbps to 320kbps, and found that they are very similar to the maximum CBR compression sound quality, i.e. 96kbps to 192kbps vbr sound is similar to 192kbps of cbr, but the former is 192kbps, 4481kb in size and the latter is 5123kb, so as a compromise method looking for higher quality sound and saving space, vbr is really useful. Of course, on the other hand, because the code rate changes, the stability is naturally slightly worse than cbr.
Fourth, in terms of mode parameters, there are stereo, J stereo, forced stereo, and mono. The comparison test shows that standard stereo has the best effect. Although the compressed file size is the largest, the file size difference is smaller, and the difference in sound quality and sense of hearing, I still think stereo is ideal.
Fifth, the compression method, there are vbr-old, vbr-new and two others in the software, but only the first two are easy to use. Comparing old and new vbr encoding methods, I found that the assumption is that in terms of sound quality, it’s still the old one. Delicate, but the compression speed of the old encoding is very slow, almost equal to 5 or 6 times that of the new encoding method. The production of a song is almost the same. in 3-4 minutes, which is very difficult to use, and the file size is also 10% larger, so it is recommended to use vbr-new for everyone, which is more convenient and easy to use.
