MP3 stands for MPEG (Moving Pictures Experts Group) Audio Layer III and is the most familiar audio coding format for digital audio files. It is also the third audio format of the MPEG-1 standard which follows ISO and IEC standards. MP3 follows lossy data compression method where the uncompressed audio file size is reduced via perpetual coding or psychoacoustic modelling. In simple words, this process of compression discards the portion of the sound file which is beyond the hearing capabilities of humans. Also, the MP3 compression reduces the quality of background sounds in the raw audio file, which is unnoticeable.
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Usually, an MP3 audio file is 10-14 times lower in file size when compared to its equivalent uncompressed or CD-quality audio file. This popular audio file format came in the year 1993 and soon became de facto in the music industry because of its low file size.
Why people felt the need of MP3 format
Back in the old days, disk space was an item of luxury and had its limitations. Uncompressed or CD-quality audio and music files required tons of space. Even a three minutes audio file almost needs 32MB (megabytes) of space. People mostly relied on CDs and DVDs, but it was way too heavy to carry all of them at a time.
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Soon, several researchers came forward and started working on a compression method which was based on the psychoacoustic masking or perpetual limitation of human hearing, also known as auditory masking. For example, you cannot hear a car passing by if a fighter jet goes past you at the same time. Why? It is because the roaring sound of aircraft masked the sound of the car.
How MP3 works?
Any CD-quality audio file follows established 44.1 kHz sampling rate. A sample rate is the number of audio samples taken per second. 1 kHz is 1000 Hz. So, 44.1 kHz equals to 44100 Hz or 44100 samples per second. Each sample consists of 16 bits of digital data which is also equivalent to 2 bytes of data.
There are two speakers, left and right, in a stereo system. Each speaker represents one channel, and each channel corresponds to 2 bytes of data. So, overall each sample is now two times 16 bits which is 32 bits or 4 bytes of data per sample. If you multiply 44100 by 4 bytes of data, then it equals to 176,400 bytes or 1411 kilobits per second.
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If we calculate the size of five minutes CD quality uncompressed audio file, then it comes down to 176,400 multiples by 60 and 5. This equals to 5,29,20,000 bytes of data or approximately 53 MB audio file size.
MP3 was developed to encode 1411 kbps data at 320 kbps or less. The lowest possible bit rates in MP3 are 32 kbps and 320 kbps respectively. 128 kbps sound quality is equivalent to radio music and 160 kbps is good enough to match the quality of CD audio file. Therefore, even a 128kbps MP3 audio file, which is almost 1/11th of uncompressed audio file bit rate, can result in 85%-90% reduction of audio file size.
Can you spot the difference between MP3 and CD quality audio file?
This is an age-old argument between an audiophile and an average music listener. Logically, there is audio data reconstruction based on perpetual noise shaping in MP3 file format. But practically, it is near impossible to spot the difference between a 160 kbps MP3 file and its equivalent raw audio file. Also, you need the best and world class music system, speakers or headphones to catch the missing piece in an MP3 file format.
I would leave this job to the best in class sound editors. It is better to appreciate the fact that now you can stuff thousands of MP3 songs in a portable music player.