How CD Burners Function

The introduction of CD burners sparked a major cultural change. This innovation allowed everyday people to compile songs and create personalized CDs. Music mix creators suddenly had control over the production process.

Nowadays, writable CD drives (CD burners) come standard in most new PCs, and more audio enthusiasts are adding dedicated CD burners to their stereo setups. In under five years, CDs have surpassed cassette tapes as the preferred medium for mixes.

This article will explain how CD burners encode songs and data onto blank CDs. We will also explore CD re-writable technology, examine how data files are arranged, and show you how to create your own music mixes using a CD burner.

Understanding CDs: The Track Bumps

If you're familiar with How CDs Work, you already grasp the concept behind CD technology. CDs store music and other data in digital format, meaning the information on the disc is represented by sequences of 1s and 0s (refer to How Analog and Digital Recording Works for more details). On traditional CDs, these 1s and 0s are signified by millions of microscopic bumps and flat spots on the reflective surface. The bumps and flats form a continuous track that's roughly 0.5 microns (millionths of a meter) wide and miles (5 km) long.

To read this data, the CD player directs a laser over the track. When the laser crosses a flat section, the light is reflected directly to an optical sensor in the laser assembly, which the CD player interprets as a 1. If the laser encounters a bump, the light is deflected away from the sensor, and the CD player recognizes this as a 0.

A CD player uses a tiny laser to follow the data track on a CD.

On traditional CDs, the flat regions, or lands, reflect the light back to the laser assembly, whereas the bumps redirect the light, preventing it from returning.

Understanding CDs: The Track's Journey

The bumps are laid out in a spiral pattern, beginning at the disc's center. As the CD player spins the disc, the laser moves outward from the center. To maintain a steady pace, the bumps pass the outer edge of the CD faster than they pass areas closer to the center. To ensure the bumps pass the laser at a consistent rate, the player must slow the disc’s rotation as the laser moves outward.

At its core, a CD player operates on a simple concept. The challenge lies in the precision required to encode and read the spiral pattern, but the fundamental idea is straightforward.

The CD player spins the disc while the laser assembly moves outward from the center. To maintain a constant scanning speed, the player slows the disc as the laser moves further from the center.

In the next section, you'll discover how data is written to CDs, whether by professional machinery or a home CD burner.

CD Reading Process

In the previous section, we discussed how traditional CDs store digital data through a pattern of bumps and flat regions, arranged in a continuous spiral. The CD manufacturing machine uses a high-powered laser to engrave this pattern into a photoresist material on a glass plate. Through a detailed imprinting process, this pattern is transferred onto acrylic discs. These discs are then coated with aluminum (or another metal) to form the reflective surface. Lastly, the disc is covered with a transparent plastic layer that protects the reflective metal from damage like nicks, scratches, and dirt.

As you can see, this process is quite intricate and delicate, involving several steps and different materials. Like many complex manufacturing processes (such as newspaper printing or television production), conventional CD creation is not suited for home production. It is only practical for manufacturers that produce hundreds, thousands, or millions of CD copies.

As a result, traditional CDs have remained a "read only" storage format for most consumers, similar to LPs or standard DVDs. For audiophiles used to recordable cassettes and computer users frustrated with the limited memory of floppy disks, this restriction was seen as a major disadvantage of CD technology. In the early 1990s, both consumers and professionals began searching for a way to create their own CD-quality digital recordings.

Creating CDs

In response to this growing demand, electronics companies developed a new type of CD that could be easily encoded. CD-recordable discs, or CD-Rs, have no bumps or flat areas. Instead, they feature a smooth reflective metal layer placed on top of a photosensitive dye layer.

When the disc is empty, the dye remains translucent, allowing light to pass through and reflect off the metal beneath. However, when the dye is exposed to concentrated light of a specific frequency and intensity, it becomes opaque, darkening to the point where light can no longer penetrate.

A CD-R differs from a conventional CD in that it lacks bumps and lands. Instead, the disc features a dye layer under a smooth reflective surface. On a blank CD-R, the dye is fully translucent, allowing light to reflect off the surface. The writing laser darkens specific areas where bumps would traditionally be, creating non-reflective spots.

By strategically darkening certain points along the CD's track and leaving other sections of the dye transparent, you can form a digital pattern that a standard CD player can read. The player's laser will only reflect back to the sensor when it encounters the translucent dye, much like how it bounces off the flat sections of a conventional CD. As a result, although the CD-R disc lacks any bumps, it behaves just like a traditional disc.

The task of a CD burner is, naturally, to "burn" this digital pattern onto a blank CD. In the next section, we'll explore the inner workings of a burner and see how it performs this process.

Burning CDs: Laser Mechanism

In the previous section, we saw that CD burners use a laser to darken microscopic areas of CD-R discs, creating a pattern of reflective and non-reflective spots that a standard CD player can read. Given the precision required to encode data on such a tiny scale, the burning system must operate with extreme accuracy. However, the fundamental process is quite simple.

The CD burner contains a moving laser assembly, similar to a regular CD player. However, it features a second laser, called the "write laser," which is more powerful than the standard "read laser." Unlike the read laser, which only bounces light off the surface, the write laser interacts with the disc's surface by altering it. Since read lasers lack the intensity to alter the dye material, simply playing a CD-R won't erase any stored data.

In the next section, you'll discover how the write laser functions.

Burning CDs: Write Laser

The write laser operates just like the read laser: as the disc spins, the laser moves outward. The plastic layer beneath the disc contains pre-pressed grooves to guide the laser along the correct path. By syncing the disc's spin rate with the movement of the laser, the burner ensures the laser follows the track at a consistent speed. To record data, the burner turns the write laser on and off in sync with the 1s and 0s pattern. The laser darkens the material to encode a 0 and keeps it translucent to encode a 1.

CD burners offer the ability to create CDs at various speeds. At 1x speed, the CD spins at the same rate as when a player is reading it, so it takes around 60 minutes to record 60 minutes of music. At 2x speed, it takes about half an hour to burn the same amount of data, and so on. To burn at higher speeds, more advanced laser control systems and faster connections between the computer and the burner are necessary. Additionally, the blank disc must be designed to support these higher speeds.

The key benefit of CD-R discs is their broad compatibility, working with almost all CD players and CD-ROMs, which are some of the most common media players in use today. In addition to their widespread compatibility, CD-Rs are also quite affordable.

The main limitation of CD-Rs is that they are non-rewritable. Once you’ve recorded the data, it cannot be erased or rewritten. In the mid-'90s, manufacturers introduced a new format to solve this issue. In the next section, we’ll explore CD-rewritable discs, also known as CD-RWs, and see how they differ from standard CD-Rs.

Erasing CDs

In the previous section, we discussed CD-R, the most common type of writable CD technology. CD-R discs are affordable, can store a significant amount of data, and are compatible with most CD players. However, unlike other storage mediums such as tapes and floppy disks, once a CD-R is full, it cannot be reused or re-recorded.

CD-RW discs take writable CDs to the next level by incorporating an erase function, allowing users to overwrite outdated data. These discs rely on phase-change technology, using a special chemical compound of silver, antimony, tellurium, and indium. Like many materials, the structure of this compound can be altered by heating it to certain temperatures. When heated above its melting point (around 600°C), it becomes liquid; when heated to its crystallization temperature (approximately 200°C), it solidifies.

In CD-RW discs, the reflective lands and non-reflective bumps found in traditional CDs are replaced by phase changes in a unique compound. When the compound is crystalline, it is translucent, allowing light to pass through to the metal layer, reflecting back to the laser assembly. When the compound is melted into an amorphous state, it becomes opaque, preventing reflection.

Phase-change Compounds

Phase-change compounds can have their phase shifts "locked in place" after the material cools down. If you heat the compound in CD-RW discs to its melting point and then cool it rapidly, it remains in an amorphous state, even if it's below the crystallization temperature. To crystallize the compound, it must be kept at the crystallization temperature for a specific period before cooling to form a solid structure.

In the material used in CD-RW discs, the crystalline form is transparent, while the amorphous, fluid form absorbs most light. On a blank CD, the writable material is crystalline, so light passes through to the reflective metal layer, where it bounces back to the light sensor. To encode data, the CD burner uses its write laser to heat the material to its melting point. The areas that are melted serve the same purpose as the bumps on a traditional CD and the opaque areas on a CD-R—they prevent the "read" laser from reflecting off the metal layer. These non-reflective areas represent 0 in binary code, while the crystalline, reflective spots represent 1.

The Erase Laser

Like CD-Rs, the read laser isn't powerful enough to alter the material in the recording layer; it's much weaker than the write laser. The erase laser is more powerful than the read laser but less so than the write laser. It doesn't melt the material, but it does heat it to the crystallization point. By maintaining the material at this temperature, the erase laser can restore the compound to its crystalline form, effectively removing the encoded 0. This allows the disc to be cleared for new data.

Unlike older CD formats, CD-RW discs do not reflect as much light, which means they are not readable by many older CD players and CD-ROM drives. Some newer models, including all CD-RW writers, are designed to adjust the read laser to be compatible with various CD formats. However, because CD-RWs are not widely supported, they are not ideal for use with music CDs. They are typically used for back-up storage devices for computer files instead.

As we've discussed, the reflective and non-reflective areas on a CD are extremely tiny, and these patterns are burned and read at a rapid pace by a fast-moving laser beam. Because of this high speed, the likelihood of encountering a data error is relatively high. In the next section, we'll explore some of the methods CD burners use to address various encoding challenges.

CD Formats

In the earlier sections, we explored the fundamental concepts behind CDs and CD burners. By utilizing precise lasers or metal molds, you can mark patterns of highly reflective and less-reflective areas that represent binary 1s and 0s. This basic system allows you to encode almost any type of digital data. There is no inherent restriction on the type of marking pattern you can create on the disc.

However, to ensure the information is accessible to other CD players or drives, it must be encoded in a recognizable format. The widely used format for music CDs, ISO 9660, laid the groundwork for future CD formats. This standard was specifically designed to reduce the impact of data errors.

This is achieved by methodically arranging the data on the CD and adding a substantial amount of extra digital information. The next section will delve into the additional data encoded on a burned CD.

Encoding Data

Several key factors contribute to making a CD readable by a CD player:

The arrangement of data on music CDs is highly intricate. CD-ROMS — compact discs containing computer files instead of music — incorporate even more advanced error-correction mechanisms. This is because a computer file error could potentially corrupt an entire program, whereas a minor flaw on a music CD only causes a bit of fuzz or a skipped section. For more information about how data is arranged on various CD formats, check out Audio Compact Disc - Writing and Reading the Data.

Certain writable CD formats require you to prepare all your data before beginning the burning process. This limitation stems from the original design of CDs and the physical structure of the disc. The long track, consisting of a continuous chain of 1s and 0s, is difficult to divide into sections. However, newer disc formats allow you to record files in separate "packets", adding the table of contents and other structures after the disc is filled.

CD burners are impressive pieces of technology, with some fascinating inner mechanisms. But for the average computer user, the most exciting part is what you can do with these devices. In the next section, we’ll explore how you can harness this technology to create your own music mix.

Creating Your Own CDs: Software

Although CD-Rs can hold various kinds of digital data, one of their most popular uses today is creating music-mix CDs on a computer. If you're unfamiliar with CD burners, the process may seem intimidating. However, it’s quite straightforward once you have the right software and understand the basic steps.

Once your CD burner is connected, the first step in the CD creation process is to load the necessary software. This music-management software performs several crucial tasks:

Most modern burners come bundled with one or more music programs, but you can also purchase or download them from the Internet. While some programs focus on specific parts of the burning process, there are comprehensive software options available that handle everything (see below). Click here to search for software related to burning your own CDs.

Creating Your Own CDs: Music

Once you have the necessary software, it’s time to collect your songs. You might want to directly rip tracks from your CD collection. To do so, you'll need to 'rip' the songs, transferring them from the CD to your computer’s hard drive. This requires an extraction program. Insert the CD into your CD-ROM or burner, select the track you want, and the software will play and re-record the song into a usable digital format. It's completely legal to copy songs you own, as long as it's for personal use.

You can also acquire MP3s from the Internet. MP3s can be downloaded from paid music sites or through file-sharing programs. While some MP3s are available for free and can be legally downloaded and burned onto a CD, many are pirated, and downloading them without permission is a violation of copyright law. To search for MP3-related websites, click here.

MP3s are compressed files, so they must be expanded (or decoded) before you can burn them onto a CD. Most music-management programs can decode these files. If you don't have the proper software, there are many decoding programs available for download on the Internet.

After gathering your songs, use your music manager to arrange them in the order that best suits your mix. Remember, you’re working with limited disc space. CD-Rs come in different capacities, both in megabytes and minutes. Today, most CD-Rs are either 74 or 80 minutes in length. Before moving on to burning your CD, double-check that your mix fits within the available space on the disc.

Creating Your Own CDs: Burning

Once you’ve perfected your mix and saved it, simply insert a blank CD-R into the burner and select the "burn" or "write" option from your music-management software. Be sure to choose "music CD" instead of "data CD" to ensure it’s playable on regular CD players. You’ll also need to decide on the burning speed. A slower speed often minimizes the risk of errors during the burning process.

There’s always a chance that things might not go perfectly when burning a CD, so don’t be too surprised if something goes wrong. Since CD-Rs can't be rewritten, any irreversible mistake means the whole disc is ruined. Among CD-burners, this is humorously known as "making a coaster"—because that’s the only use left for the ruined disc.

If burning CDs is consistently problematic, your drive might be malfunctioning, or your music-management software could be the culprit. Before returning the burner, try using different programs to see if they deliver better results.

Creating a CD-ROM follows a similar procedure, but this time you’ll format the disc as a data CD rather than a music CD. Some modern CD and DVD players are capable of reading MP3 files directly, meaning you could use this method to make a CD-ROM music mix. Since MP3 files are compressed, you can store a lot more on a single disc, allowing for longer mixes. However, the downside is that the disc will not work with most standard CD players.

CD burners have revolutionized what the average computer user can do. Not only can you record music that will play on almost any CD player, but you can also create CD-ROMs filled with photos, web pages, or movies. With a device the size of a car stereo, costing about as much as a budget bicycle, you can launch your own multimedia production business!