Really terrifying audio compression
Check the deterioration of sound quality by “appearance”!
■ What format do you choose when copying? AIFF, ALAC, AAC … Check the sound quality of each by “appearance”
Music files are the main audio playback source for Imadoki. Except when purchased from online distribution, the sound quality of the music files used here is largely related to the work of reading audio data from a CD to a PC, the so-called “ripping” setting. This time I would like to review that part in a little more detail.
The first half of this article describes the basics of the extraction format for those who want to know what quality of sound to choose when extracting. Perhaps this first half is common information to many file and web readers.
However, the highlights are beyond that. “Really Terrifying Audio Compression” … So, in the second half of the article, “How much does the compressed file actually deteriorate the sound?” And “How much does the sound quality change depending on the bit rate value?” you will check with (→ Visually check the sound quality of AIFF, ALAC, AAC!). I would like you to stay with us until the end.
■ Not to mention now … First, let’s review the basics
The scheme of the options for copying is “compression format (file format)” and “bit rate”. These two determine the sound quality and file size, which is another important factor.
“Compressed format (file format)” refers to formats such as AAC, MP3, Apple Lossless, and FLAC. This selection determines the sound quality, file size, and playback environment.
The “bit rate” is the amount of data allocated per second of audio. The higher the value (kbps), the higher the sound quality, but the larger the file size.
In the case of iTunes, call this screen “Load Settings” from the environment settings and configure the extraction.
Please refer to the following table based on that. We have summarized the characteristics of typical compression formats and bit rate settings.
The item “Sample bit rate settings” in the table is cited from the default settings provided in iTunes (* iTunes does not support FLAC)
First, pay attention to the second item from the left of the table. Compression formats can be broadly classified into “lossy compression”, “lossless compression” and “uncompressed”.
The “lossy compression” method, which AAC and MP3 belong to, achieves a high compression rate = a significant reduction in file capacity by reducing some of the data when compressing audio data. In contrast, the original audio data cannot be fully restored during playback and deterioration in sound quality is inevitable. The degree of deterioration in sound quality changes depending on the bit rate setting. The lower the value of the bit rate, the greater the deterioration in sound quality and, conversely, the higher the value of the bit rate, the more mitigated.
The “lossless compression” method, to which Apple Lossless and FLAC belong, is a method that can fully restore the original audio data during playback, at the cost of a low compression rate. The file size is large, but the sound quality is equivalent to that of a CD. The bit rate fluctuates automatically according to the content of the audio data, and the compression rate is not constant accordingly.
AIFF and WAV are “uncompressed” methods. Extract the original audio data and create a file as is. It does not compress, so it has a lot of capacity, but the sound quality is perfect.
