Techniques for enjoying compressed audio with high sound quality
I converted a music CD to MP3 or WMA, but the sound is not good … Many users will think so. So, let me introduce you to one of the methods to do high quality audio compression.
Sound quality is improved by lowering the volume of the extracted WAV file and then encoding it in MP3 or WMA.
There are various audio compression methods like WMA, AAC, Ogg Vorbis for MP3. They are very convenient because they can compress the file size to about 1/11 (at 128 kbps) compared to WAV. However, these are called lossy compression and sound quality degrades slightly because compression is done by reducing sound information to the point that it is difficult for the human ear to understand. If you really stick to the original sound of a music CD, you should use WAV as is, or use lossless (lossless) compression like WMA Lossless, Apple Lossless, FLAC.
However, even with MP3 and WMA, if it is compressed well, many people will not notice the difference in sound quality. Generally, a bit rate of 128 kbps is used, but if you increase it to 160 kbps or 192 kbps, the amount of data to be reduced will decrease and the sound quality will improve.
If you can’t tell the difference from the original sound by listening to the lossy compressed sound, that’s fine, but it is troublesome that there are cases where you can clearly see the deterioration depending on the song. Specifically, there is a clip-like beep, and the cymbal and hi-hat sound is clearly distorted. This is not just a problem to be solved by increasing the bit rate, it has nothing to do with the lack of high frequencies. This happens because the music data matches the weak points of the compression algorithm.
The weak point is that it is vulnerable to the sound applied by the compressor (equalizing the maximum volume). In other words, it is vulnerable to loud and continuous sounds. In particular, the recent J-Pop is made by applying a compressor to gain sound pressure and setting it to maximum volume, so it can be said that it is the music data that is vulnerable to compressed audio.
Therefore, if you process the WAV data a little before compressing it to MP3 or WMA, the sound quality will be drastically improved and clipping phenomenon can be avoided.
The process is simply to lower the volume level of the entire song. Of course, it’s burning, so you can’t mess with the volume of CD playback or squeeze the volume from encoding software like Windows Media Player. It is necessary to rewrite the waveform of the WAV data using waveform editing software and lower the volume level. Specifically, it is safe to lower the level by about -6dB. This will cut the volume in half, but due to the features of the compression software, it doesn’t appear to be as quiet. If possible, it is even more effective to apply an effect called an expander to eliminate the compressor effect.
