Making Music
  Computer Music Software and Hardware

Write again

Another development to help users get the most from CDs is CD-RW. You can't write to a normal CD more than once because the writing process burns pits into the CD with the laser. CD-RW, however, uses a different material and the laser changes its state from crystalline to amorphous, enabling it to be written to many times.

However, the reflectivity from CD-RW is not as great so standard CD players, including some computer-based CD drives, may not be able to read them - drives need to be CD-RW compatible to do so.

It's also unlikely that audio CD players will be able to read them. Needless to say, you need a CD-RW drive in order to write them.

CD-RW was useful when blank CDs cost a fiver but now that they only cost a few pence it's not such a big deal if you waste a few.

Your disc runneth under

The most feared error in CD burning is 'buffer underrun'. The writing process takes place in real time and the CD-R's buffer must always contain data to feed the laser. If the buffer empties the CD becomes a drinks mat. The likelihood of a buffer underrun error increases as writing speeds increase. Large buffers, therefore, are a Good Thing.

In 1999 a new technology surfaced called Burn Proof which supposedly stands for Buffer Under RuN error Proof although it's a neat name anyway and it's been trademarked by Sanyo. It's a function of the hardware and firmware in the CD-R/RW drive and it essentially puts the burning process into pause if the buffer empties during a burn without damaging the CD. Truly an excellent idea.

You do need a Burn Proof drive to use this. Most modern drives tend to include the technology and most software supports Burn Proof, too.

Give me more

Overburning sounds like it might be related to buffer underruns but it's not. It's the process of squeezing a quart into a pint pot or, more specifically, the art of squeezing more than 74 minutes of audio onto a 74 minute CD. At least it was originally. Now you can buy oversized CD blanks such as R90 and R99 that promise playback times of up to 100 minutes. The extra data is achieved by putting the tracks closer together.

The overburning process requires that the CD-R be physically able to overburn and the CD-R software must support it, too. It's often a good idea to limit the write speed to 2x or 4x at least until you discover what your system - CD-R and CD - are capable of.

The main problem with oversized CDs, assuming you can burn them in the first place, is that they may not be recognised by many playback systems. In fact, with any home-burned CD you run the risk of it not playing in a car multi-CD changer for example, and this risk increases the more a CD is overburned. However, there are so many variables involved that you need to try it see what the resulting CDs play on.

Most people used overburning in order to, er, duplicate commercial CDs that were longer than normal. If you keep your demands modest, such as overburning a R74 to 76 minutes, there's a greater likelihood they will play on other systems.

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