|
Writing or burning a CD is easy right?… wrong! It may seem easy. After all, you prepare your data, stick in a folder and press burn. Then just to be safe you make sure you can read it in your desktop PC.
But we have all burnt a “bad” CD before. It either didn’t burn, or got jammed, or stranger still it seemed to burn OK but wouldn’t read when we tried to test it in another machine.
So what happened? Well a closer look ‘behind the scenes’ thanks to some information published by Dr Jerry Hartke of Media Sciences in the March edition of Medialine reveals the complex process of burning a CD.
A CDR contains a layer of organic photosensitive dye. The different colours you find on the market are different dye formulations. As the dye is photosensitive, its properties are changed by contact with light. Your CD recorder uses a laser to change the chemical properties of this dye layer during the burning process.
CD recording is a multi-step process that is based on complex drive and disc interactions.
First, your write drive reads information on the CDR. This information was embedded in the pre-groove lead-in area of the disc by the manufacturer and contains critical information such as recommended write power and important target parameters that enables the drive to accurately evaluate recording quality. This information also specifies the maximum start of lead-out, thereby limiting recording capacity. Other information may contain write strategies, allowable speeds and applications of the disc.
Next the write drive will go to an area that is also inside the lead-in area and therefore inaccessible to a normal CD ROM drive. This area is called the Optimum Power Calibration (OPC) area. Here test recordings are made at 15 different power levels (in one-of-100 OPC partitions) each appropriate to the desired recording speed.
The results of these test recordings are then compared to target parameters. The closest match will determine the optimum power level that the drive will use to record the information.
The last area the write drive goes to is the Program Memory Area (PMA) and it is also inside the lead-in area but after the OPC area. Incremental write process, that is if you are writing your disc in Track-at-Once mode or a multi-session disc, use this area to temporarily store information that will eventually be written as a Table Of Contents (TOC) in the lead-in area when the disc is closed.
Poor media or drive quality may prevent the writer from reading the PMA, causing the writer to hang after the tracks are written. CD ROM readers cannot access these discs because the TOC is missing, but a CD Writer may be able to subsequently read the defective PMA area and therefore read the CD.
CD recording is a sophisticated process. Quality requirements become more demanding as speeds increase and multimedia applications multiply. The components of your CD writer strongly influence the quality of the data being written to your CDR/CDRW. The improved features and low prices of CD writers have resulted in rapid installation in computers from homes to offices around the world. However these cost pressures may also lead to design and manufacturing compromises as manufacturers look to recover margin.
These may not immediately cause poor recording yields, but can result in quality differences that appear later as CDR media interchange failures. Such deficiencies often remain hidden unless users test the recorded discs for quality.
Comprehensive testing of your CD masters is carried out as a matter of process when you replicate CDs with EverTechnology. The testing reports on the CDs quality and may result in your master being rejected as a suitable master for replication. Should you ignore this reporting, the replications may prove to have serious CD ROM reader compatibility issues.
EverTechnology can help you with information on ways to burn your CD that will increase the likelihood of creating a high quality CD master assuming quality media and CD writer. Contact us for details.
More Articles... |
