By Request DJ & Karaoke Company

MP3+G is a relatively new karaoke format that uses the compressed digital audio format of MP3 with the standard graphic format of traditional CDG. It features all the benefits and drawbacks of standard MP3's while retaining the graphical "glory" of CDG's. This article is designed to be a fairly technical primer of what goes into making and MP3+G as well as what makes a CD and a CD+G disc.

First we should give some background information on what makes a CDG different from a standard compact disc. A standard compact disc is something like an old vinyl record. Like vinyl records which stored music in a groove that had "bumpy walls" to wiggle the needle, the music on a CD is stored in a line of pits and troughs (representing the ones and zeros of a digital signal) that "wiggle" the laser used to read the data. Unlike a vinyl record which spirals from the outside in, data on a CD spirals from the inside out.

Another key difference between a standard compact disc and a vinyl record is that the "data" on a record is one continuous "line", whereas the data on a compacy disc is broken into segments known as "Sectors". A standard CD player playing at 1x (150 kbps) reads 75 sectors per second. Each sector is divided into 2448 bytes. 2352 bytes of the data are devoted to music, and the other 96 are divided into 4 data packets of 24 bytes each. 8 bytes of this 24 byte packet rae overhead (meaning they do useful technical things like data parity for error checking). The remaining 16 bytes in the packet are then broken into their constituent bits (8 bits to the byte), and these bits are further divided into "sub-channels" which are labeled P through W. This means there are sixteen bits of subchannel information in each 24byte data packet.

This is where a CDG starts diverging from a standard CD. The P and Q subchannels are used by most CD players for timing information so that the CD player knows where it is on the disc, how much time is left on the disc, how much time is left on this track, etc. The R-W subchannels are unused by standard CDs (although players supporting the CD-Text standard read a block of information at the beginning of the disc which gets stored in these R-W subchannels). However, a CDG uses these subcode channels to store the graphical information component that gets turned into the lyrics on a karaoke singers screen. Since there are only 6 bits of information used to carry the graphics and because there are only 16 bytes per packet, 4 packets per sector, and 75 sectors per second, this works out to 3.6K (28,800 bytes) per second. This is not a lot of information!

Now, as most of us know, MP3 works by reading the standard audio data and compressing it using various technics like only keeping the differences between the left and right audio channels and getting rid of frequencies which are typically beyond the average human's hearing range. At a sufficiently high encoding rate, MP3 audio is nearly indistinguishable from an audio CD (which is itself a lossy compression format). In a crowded bar, the two are even more indistinguishable.

But what of the "G" component in MP3+G? Well, it is simply all of those bits from the R-W subchannels. Applications like Audiograbber, which can rip CD+G discs, simply create a file containing those R-W subcodes and place them in a file witha .CDG extension. So in reality, there is no such thing as an MP3+G file. Instead there is the MP3 file and a corresponding CDG file. The application used for playing back the MP3+G simply knows to play the MP3 normally while also reading from a CDG file with the same name as the MP3 file. That's why its so important that you name your files carefully!

An unfortunate side effect of the standard ripping process is that the CDG file is often several megabytes in size. This tends to waste a lot of space on computer hard drives. For example, if your song is approximately 6MB, the corresponding CDG file will often be 3 or 4 megabytes in size. If each song takes up 10MB, and standard 200GB drive (which really isn't 200GB) can only hold 20,000 songs. While this is an impressive collection, many KJs have far more than 20,000 karaoke songs. Fortunately, the CDG file is highly compressible using the standard ZIP format and often compresses down to about 90% of its original size without any loss in graphics quality (because ZIP is a lossless compression format). This means that our 10MB song (6MB for the MP3 and 4MB for the CDG) can be compressed to approximately 6 or 7 megabytes. Now our standard 200GB hard drive can hold between 28,000 and 33,000 songs. As an added bonus, you can put both the CDG and MP3 files into the same ZIP file, thus giving you only one file to manage instead of two seperate files to manage. It is this resulting ZIP file that is most commonly refered to as an MP3+G or MP3G.

And that's it in a nutshell. In this article you learned what makes up a CD, a CD+G, and finally an MP3+G file. Many great resources exist on the web for those wanting to get even more technical.

If you are new to MP3+G or are a KJ looking to convert existing CD+G's to MP3+G, we highly recommend Audiograbber and our freeware component called "MP3+G to ZIP". MP3+G to ZIP combines the MP3 and CDG files output by Audiograbber into one nice ZIP file automatically. To play back these MP3+G's on your computer, check out WinCDG Pro.