Is the compressed sound bad?
Recently, there are more and more opportunities to reproduce audio and music from compressed sound sources, such as digital televisions and iPods.
I think many audiophiles naturally hate “The sound of compressed sound sources is ridiculous,” but is that true? Here, I will try to discover the truth based on the data.
Types of compression with loss
The principle and format of audio compression will be left in the hands of Wikipedia, but here we will focus on the most used MP3 and AAC (Advanced Audio Coding) methods. It is said that AAC is a newcomer and has a high sound quality. Here is a relatively easy explanation of understanding of AAC compression. The source is a lighting book on digital technology that I wrote before, but I forgot the title of the book.
It should be noted that a high sound quality here means that the theoretical fidelity to the original sound is high, and does not mean that sound is good to listen. If the same compression method is used, the higher the number of bits sent per second, that is, the bit rate (unit: kbps), the greater the sound quality. However, since the bit rate can be a variable bit rate that fluctuates according to the amount of information, comprise that the values on this page indicate the average value or the lower limit value.
The sound quality of the compressed sound source is always confirmed by a blind test.
As I wrote on the page of the Ptolemaic theory to the Copernican theory, in Japan, the blind evaluation of audio equipment is considered taboo and never realized. The reason is evident, because if you do this, the audio industry will not be possible in the first place. However, audio compression technology is different. This is an essential technology for the most recent audio equipment, such as digital television, music distribution and portable audio equipment, which is expected to have a great demand in the future, instead of aiming the world of narrow audio and narrow where they are not similar. -The science is very widespread. It is extremely important to evaluate through a blind test how much data can be compressed without feeling the deterioration of sound quality, and is a first-line engineer who has dominated the last psychoacoustic and the theory of digital information. It has been introduced and developed.
At this time, unlike the evaluation of other audio equipment, it is easy to change the difference between the compressed sound source and the original sound source so that the operation is not understood, only with computer software, so a Perfect double double test is easy. I am also happy to be able to do it.
“About the sound quality of audio compression technology” is very useful. I also agree with the claim of this site.
Evaluation of the bit rate and sound quality
This site contains the results of a blind test to see if there is a difference in sound quality between a compressed sound source with a different bit rate and a PCM WAV file (same as the sound of a CD). However, it does not say what the format is.
The subjects were 220 sound professionals, and the results were such that the difference was barely noticed if it was above 100 kbps, or even if it was known, I would not bother me. The stereo bits speed in BS digital mode and the default iPod speed is 128 kbps or more, so it is a subtle point and can be said that a young and deaf person can notice the difference.
What is the difference reflected in the bit rate?
Why does the sound differ when the bit rate is different? To answer the question with precision, it is necessary to understand the compression principle, which is quite difficult without the basics of psychoacoustics and the theory of information. The most significant reflection is the frequency characteristics of the reproduced sound, which appears as a difference in the cutoff frequency in the high frequency range. The following sites show the frequency features of the sounds played with different bit rates.
