A little review. The secret of compressed sound source (MP3)

Let’s review the music compression technology, such as MP3, which is too common to be talked about recently.

MP3 data is 10% of CD.

The data volume of MP3 is about 1/10 of CD (in case of 128kbps).
One minute songs are compressed to about 1MB.

This compression technology and the increased capacity and lower cost of flash memory have sparked an unprecedented portable audio boom.

In a very small memory, all the CDs in the house are stored.
ApThe word “compression” here.art from the sound quality, this is very useful.

The word “compression” here.

If it is a ZIP file of a personal computer, the compressed file can be completely restored to its original shape.

However, most compressed sound sources such as MP3 cannot return to the same data as the original CD.

This is called “lossy compression”.
Conversely, compression that can be restored like a ZIP file is called “lossless compression”.

Therefore, MP3 was often said to have the same sound quality as a CD, but it actually cuts (discards) considerable data.

So how do you cut one tenth (90%) compared to a CD?
It uses technology that makes good use of the characteristics of the human ear.

1. The human ear has different sensitivity between high and low sounds

The human ear does not hear the volume change, even if there is a slight volume change for the “high sound”.
Conversely, “low sounds” can be sensed sensitively if there is any change in volume.
Using the characteristics of this ear, the volume data on the treble side is deleted to reduce the amount of data.

mp3_1_en

2. The human ear cannot hear very small sounds

Human ears have the lowest volume that can be heard depending on the frequency.
You can hear the lowest sound around 2kHz-5kHz of human voice.
Other “low sounds” and “high sounds” cannot be heard by the ear unless the volume is raised to some extent.
Therefore, the data of “low sound” or “high sound” of small volume is cut off entirely.
There is no problem because you can’t hear it originally.

mp3_2_en

3. I can’t hear the small sound behind the loud sound

If several sounds are sounding simultaneously in a similar frequency band, the human ear will only hear the loudest sound.
That’s why you can’t hear it even when you’re loud and noisy.

So small sounds that are hidden by loud sounds are not audible to the ears, so there is no problem cutting them.

mp3_3_en


From the characteristics of the above three ears, the parts that do not respond to the hearing cannot be sharpened.
Conversely, 90% of the information you hear may or may not be present.

But it is. 128kbps MP3 is definitely different from CD.
I think “same sound quality as CD” is a bit too much.

 

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