This section contains more in-depth information about MP3 than what is covered in the other pages of my site. If you have any corrections or additional information, please e-mail me at mrpotatoz@juno.com
Let's start with the basics, eh?
Why does audio need to be compressed?
CD quality audio is sampled at 44.1 kHz, stereo, and with a resolution of 16 bits per sample. One minute of CD audio will take up about 10 MB of storage space. No big deal for today's storage capacities, but most songs are longer than one minute and archiving multiple songs (or even albums) will require lots of disk space. To download one minute of uncompressed CD quality audio, it would take about 40 minutes for the typical 56k modem connection.
What is digital audio compression?
Digital audio compression is the process of minimizing storage space requirements for audio data.
Modern perceptual audio coding techniques (like MP3) exploit the properties of the human ear (the perception of sound) to achieve a size reduction with little or no perceptible loss of quality. This is why codecs such as MP3 and Liquid Audio are called lossy or perceptual compression. Inaudible and extraneous parts of the audio are not kept. The resulting file can sound the same, but it can never contain the same amount of data. Also, the data lost during the encoding process cannot be retrieved.
Digital audio compression consists of two parts. The first part is called encoding (compression) and is done by an encoder (such as LAME). Encoders transform digital audio data in, for example, WAV files (*.wav- natively recognized by Windows as a data file containing audio data) into a highly compressed form called a bitstream.
The second part is called decoding (decompression) and is done by a decoder (such as WinAmp). To play the bitstream on a computer you need a decoder. A decoder transforms the bitstream back into a WAV file for ouput. The decoded WAV can also be saved to disk (ex. if you want to record an audio CD with the WAV).
Because of the two parts of digital audio compression (compression and decompression), digital audio compression schemes are often called codecs for short.
What is MP3?
MP3 is an audio compression scheme and is short for MPEG-1 or MPEG-2 audio, layer 3. The *.mp3 data file format stores compressed audio digitally on computer media.
What is MPEG?
There are two definitions of MPEG:
1) MPEG can stand for Moving Picture Experts Group, a group working under the joint direction of the International Standards Organization (ISO) and the International Electro-Technical Commission (IEC). This group works on standards for the coding of moving pictures and audio.
2) MPEG 1 is also the name of the family of perceptual coding schemes used in the compression of audio signals. It specifies a family of three audio coding schemes, simply called Layer 1, Layer 2, and Layer 3. The terms MP1, MP2, and MP3 are derived from the names MPEG 1 Layer 1, MPEG 1 Layer 2, and MPEG 1 Layer 3. From Layer 1 to Layer 3, encoder complexity and performance increases, but so does the amount of CPU power needed to decode the files.
The decoders of the three codecs (MP1, MP2, MP3) are backwards compatible (e.g., a Layer 3 decoder may accept Layer 1, 2,and 3, whereas a Layer 2 decoder may accept only Layer 1 and 2.)
Mrpotatoz, what are some of the vocabulary words we should know about relating to MP3? I made this one up ;)
[ Bitrate ]
A term widely used in audio compression. It is the average number of bits that one second of audio data will consume. The unit used is kbps (1000 bits/s).
A 128 kbps MP3 file that is 60 seconds long has a size of 7680 kbits or 7 680 000 bits or 960 000 bytes (8 bits to a byte) or 960 Kbytes (1000 bytes to 1 Kb) or about 1 MB. A 128 kbps MP3 is about one-tenth of the original WAV file.
[ CBR ]
The most common method that ensures a consistent bit rate throughout an encoded file, potentially at the expense of audio quality and/or encoder efficiency.
When using CBR, every frame of the MP3 is allocated a specified number of bits and has to compress the audio data corresponding to that frame with the number of allocated bits. Sometimes the allocated number of bits is insufficient, sometimes it is too much, rarely is it just right.
Use CBR encoding when you need to produce consistent file sizes (ex. for streaming over an internet connection). CBR encoding is faster than VBR encoding.
The main pages of this site show beginners how create MP3's with CBR in mind.
[ VBR ]
An encoding method that ensures consistently high audio quality throughout an encoded file by making intelligent bit-allocation decisions during the encoding process.
VBR encoding is a lot slower than CBR encoding. Use VBR encoding to achieve high quality and smaller file sizes. Also used when predictable encoded MP3 file sizes are not critical.
When you view the bitrate of a VBR file in an MP3 player, the bitrate will either change constantly or the player will display the average bitrate of the file.
The efficiency of the allocation of bits is heavily dependent on the encoder used. I have not tested VBR capabilities of Fraunhofer or Xing encoders extensively, but from what I hear, LAME is the only encoder with an efficient VBR engine. LAME VBR files result in high quality with the minimum size need to achieve that high quality.
[ Joint Stereo ] - partially adapted from www.r3mix.net
Under a given frequency the human ear no longer able to locate the spacial origin of sounds. The the encoder can exploit this fact by using what is called joint stereo. Using joint stereo, the encoder analyzes each piece of the original audio file and chooses either real stereo (left channel and right channel) or ms stereo (audio is encoded using a middle channel, contains the similarities between L/R, and a side channel, contains the differences between the L+R middle channel. MS because middle/side.).
J-Stereo allows the encoder to choose the best stereo mode for each frame: stereo or ms stereo. No stereo separation problems occur in well implemented JS modes because when there is too much difference between the L and R channel, real stereo will be used on that frame. All the frames that are encoded in ms stereo benefit from the lower bitrate requirement and can thus use the extra bits for more accurate encoding.
Joint stereo is commonly used with MP3's with a bitrate of 128 kbps or lower to improve the quality. It is not commonly used at higher bitrates because there is a misconception that joint stereo produces lower quality MP3 files. This is due to the fact that the Xing and Fraunhofer encoders do not have well tuned joint stereo capabilities. With Lame, joint stereo can be safely used at all bitrates, although a small possibility of error still does exist (though I have not experienced or heard about any problems with joint stereo under LAME).
Why is MP3 such a controversial topic?
MP3, like all file types, has both legal and illegal uses. It is legal to make or download MP3's of albums you own to keep for yourself. It becomes illegal when you sell it (giving it away is also considered sale- like marijuana!) to someone who does not own the original album. It is also illegal to possess MP3 from an album you do not own.
MP3, because of its high quality and small file sizes, has become extremely popular on the internet these past few years. It was never practical to download and trade music over the internet until the advent of the MP3 codec. Much of the MP3 trading occurring online falls into the illegal cateogory, but there's no effective way of controlling it. This has big companies, such as the RIAA (Recording Industry of American Artists I think), and some artists, like Metallica, flustered because people are obtaining music without putting money in their pockets!
There's a whole lot more to it. The music industry of today is so dumb. Most big time artists don't realize how MP3 could benefit them. MP3 bypasses the middle man (RIAA). It could bring the artists more of the profits. It upsets me to have to pay $15 for a CD that cost a quarter to make (seriously). It upsets me that the artists of the CD's I buy are popular because the RIAA put them in the spotlight. Lots is going to be happening with the music industry in the next few years, so hope for the best!
How do I configure Exact Audio Copy to work with my computer?
Find 'drive options' under the EAC menu and go to the 'drive' tab. Hit 'autodetect command now'. Then head to the first tab and let it 'detect drive features'. After that, select the ripping method that matches what EAC reported, and you can start ripping tracks.
How do I configure RazorLame to use your recommended settings?
You need to download both LAME and RazorLame first. Once you have placed them into a folder, open RazorLame and hit 'Options'. On the 'General' tab, you must locate where LAME is located and also specify a location for the MP3's to be placed once they are created. You can skip over everything else and head to the 'Expert' tab. There place either "-b 320 -h" or "-V 1 -b 128 -m j" in the 'Custom Options' box. Be sure to check the little box beneath it that says "Use only custom options".
Be sure to delete the source WAV's after encoding, they take up a lot of space.
What is the "Nitrane bug"?
The Nitrane bug is a serious flaw in WinAmp's decoding engine, which is called Nitrane. This bug affects WinAmp's ability to accurately decode frequencies below 100 Hz. Nullsoft has known about this for awhile now, but they have chosen to ignore it and continue to release updated versions without addressing this issue. To prove the bug exists to yourself, turn the equalizer on, turn up the first two bands and turn the rest all the way down.
Now load a song with some bass in it and play it. You should here obvious ditortions. I refer to this phenomena as "farting sounds". The newest WinAmp version (2.64 at the moment) has not fixed this.
How do you fix the Nitrane bug in WinAmp?
Visit www.geocities.co.jp/Technopolis/9674/in_mpg123.html and download the latest ZIP file containing the Shibatch mpg123 decoder. Someone named Shibatch has developed a plugin for WinAmp that replaces the Nitrane MP3 decoder. It decodes MP3 more accurately than Nitrane and eliminates the "farting sounds".
To install the plugin:
'Close' WinAmp preferences and you can start playing MP3 files with awesome sound quality!
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