Direct Overwrite Moves MO into Audio/Video

Posted on July 01, 1998


Direct Overwrite Moves MO into Audio/Video

LIMDOW technology may make magneto- optical a player in audio/video/multimedia applications.

By Mitch Capriano

Most professionals in the recording industry will agree: When you`re streaming production data, time is money, and although optical disk drives are reliable and comparatively inexpensive, standard magneto-optical (MO) technology is inherently slow--even when file sizes are reduced by compression.

In many cases, however, direct-overwrite optical drives can solve the performance problem. LIMDOW (Light Intensity Modulation Direct OverWrite), for example, provides the fast throughput necessary for broadcast applications, video production, editing, computer graphics animation/capture, and film production. Users can back up their tracks, perform edits, locate key points, etc., directly to LIMDOW drives.

Few people understand the work involved in turning raw recordings into marketable products. Sound editors must remove background noises, re-record muddy segments, and get just the right mix of dialogue, sound effects, and music. Video editors must adjust color and contrast, cut and splice clips, and coordinate with special effects to create the maximum visual effect. Each project is deadline-oriented and fueled by economics: the sooner the films, videos, and CDs are delivered to theaters, radio and TV stations, and music stores, the sooner studios can begin recouping their investments and start realizing profits. It`s a difficult, time-consuming process.

Today, experienced A/V editors rely on advanced technology to speed post-production work. While they have already achieved tremendous improvements by digitizing their work, storage requirements--and costs--continue to climb. Sound designers and video production houses with ad hoc approaches to increasing their storage capacity (e.g., by adding large hard drives on a piecemeal basis) are discovering that incremental additions are both expensive and difficult to manage. With direct-overwrite drives, users only have to add disks.

With a capacity of 2.6GB and a sustained write performance rating of up to 4.3MBps (10MBps burst), LIMDOW drives approach the speed and performance of low-end hard drives. In fact, these direct-overwrite drives have write transfer rates that are 100% faster than those of most other optical drives. Data transfer rates are further enhanced in some drives with as much as 4MB of cache memory. In addition, the drives provide uninterrupted data flow, which eliminates pauses, motion flicker, and sound distortion.

LIMDOW drives also use reliable, rugged removable direct-overwrite media, which allows them to meet the demanding requirements of most of today`s high-speed, nonlinear digital audio and video-editing systems.

Today`s special effects (music, animation, video, multimedia, and motion picture) call for fast access to large libraries of images and sound segments. Digitized audio signals, 3D graphics and modeling, animation, and high-resolution videos also require enormous amounts of storage. For example, each studio-quality digitized TV frame typically requires 1MB of disk space.

Audio Engineering

Audio production and post-production engineers work in real-time with artists, producers, technicians, and studio executives to ensure that sound editing has optimum impact. Even with advanced digital technology, the laborious process requires weeks or even months of 15- to 18-hour days.

Advanced dubbing capabilities require reliable, yet affordable high-capacity storage. LIMDOW technology has doubled the drive`s performance and reach to include such applications as storage for audio track development.

Studios use computers to scan and convert video and audio clips to digital files. To speed the creative process and deliver a quality finished product, engineers and artists use production-editing or effects-editing and composition systems. Production-editing systems incorporate video compression and are used for off-line editing, documentary, and corporate work. Effects-editing/composition systems are now standard in the motion picture and video industries.

Random-access digital systems speed the editing process and deliver a higher-quality finished product than do traditional techniques. The combination of digital recorders and LIMDOW drives maximizes the inherent benefits of MO while preserving the familiarity of tape. The drive`s fast write transfer rates translate into a recording time of 225 tracks per minute, or 28 minutes per 8-track using 2.6GB MO media.

Unlike tape drives, which require constant fast-forwarding or rewinding to locate particular sections, LIMDOW drives offer fast random access. Locating any point is virtually instantaneous, so the drives are cost-effective solutions for music and post-production applications. The recorders use 2.6GB removable MO disks for recording, playing, and backing up 16- or 24-bit digital audio at sampling rates of up to 48KHz.

Film Production

Direct overwrite gives professionals all the benefits of digital files (e.g., crews no longer have to cut and splice strips of celluloid), while protecting data from damage or loss. Files stored on removable direct-overwrite disks can be moved from workstation to workstation, from operation to operation, without affecting the integrity of the data--an important fact considering that data loss can cost hundreds of thousands of dollars in rework.

LIMDOW drives are also convenient for audio and video professionals since a separate cartridge can be used for each project--and a complete audio or video production library of disk takes up only inches of shelf space. Also, the rugged media, which provides over a million overwrites, protects files from hard-disk crashes and rough handling. Because the media is durable and compact, it can be easily moved among development/production workstations or shipped to other production facilities.

Enabling Technologies

The use of shorter wavelengths (from 730 nanometers to 685 nanometers) has allowed MO manufacturers to improve MO`s storage capacity and read performance. Since shorter wavelengths mean smaller data marks, the distance between tracks can be decreased from 1.39 microns to 1.15 microns.

Designers are also using new data encoding techniques. More information can be stored and read in a given amount of disk space just by switching from pulse position modulation (PPM) to pulse width modulation (PWM). The mark for current PWM recording code (Run Length Limited or RLL 1,7) can be any size up to a maximum of seven zeros.

One of the advantages of MO media is its ability to handle a relatively high number of erase cycles. MO disks have been demonstrated to perform more than a million write/erase cycles. In addition, the media has a data storage life of more than 30 years, which is sufficient to meet even the most critical information retention requirements.

MO technology combines elements of both laser and magnetic technology. Instead of using a magnetic read/write head, as in hard-drives, MO uses a laser beam to change the temperature of the media to allow it to be written on by a magnetic field. MO drives are designed to eliminate head crashes or other head-media contact. Although the head may stop reading if severely jarred, it will find its way back to the track and continue writing when the vibration stops. Once new data is written to the MO media, it is permanently stored, impervious to stray magnetic fields and other contaminants.

With current MO technology, data is written to the disk when a laser heats the surface of the media to the Curie temperature, or the temperature at which polarity is reversed (about 200 degrees). The heated area aligns itself with the polarity of an adjacent bias field. A switchable electromagnet is used to record the data as "1s" or "0s." To remove the data, a separate erase pass is required to set each data bit to a "null" state. After the process is verified, a new data bit can be written during the media`s next pass under the laser.

To read data, a lower laser power is passed over the bit. The Kerr effect, or magnetic orientation of the recorded bit, causes a slight polarity rotation in the reflected beam, which is detected by the drive`s optical system.

Over the years, conventional MO technology has become associated with well-defined drive/media interchange standards and has received widespread acceptance, with multiple drive and media sources. However, while lower prices and higher capacities have been instrumental in the growth of the optical industry, applications for MO have been limited. The concern: slow write speeds. Since multiple passes are required to overwrite data, write speeds are 50% slower than read rates--a key consideration for many users, especially those in the audio and video industries, since the write function significantly affects performance when storing or backing up large files.

Breaking the Write Barrier

To achieve Direct-OverWrite (DOW) functionality, Light Intensity Modulation (LIM) technology combines eight-layer media (non-DOW MO media has only four layers)--each with a different magnetic characteristic and Curie temperature--with two laser intensities to record new data directly onto the media. In addition, a permanent initializing magnet has been added to the optical drive.

The key to LIMDOW technology is the laser`s multi-intensity capability. By modulating the light, rather than the magnetic field, the drive`s read and write performance approaches that of hard drives. In addition, the media is substantially more reliable and has a longer data life than either hard drives or tape.

On high power (8mW to 12mW), the laser writes to the media; on medium power (4mW to 6mW), it erases. The laser changes in nanoseconds, immediately magnetizing the media`s memory layer through the intermediate layer without requiring bias-field switching. Instead, the initializing and switching layers facilitate the correct magnetization of the writing layer for the overwrite function. Set to a lower intensity, the laser reads with no change in performance, compared to non-DOW drives.

Once the new data is written, the data is read using a lower laser power level (1.25mW). The new data is safely stored and is not affected by stray magnetics or contamination, which can destroy data on standard hard drives. The MO media remains polarized and retains data until the laser is applied to the data bit at the Curie point.

In addition to providing "on-the-fly" recording and editing, the LIMDOW approach produces a longer-life platform. Running at half the duty cycle of other drives doubles the laser life. The drives are also designed with a simple nonmotorized loading mechanism that provides faster spin-up times and a longer service life, compared to complex motorized loading designs.

A number of optical storage manufacturers have adopted LIMDOW technology. As a result, LIMDOW drives are backward compatible with the previous two generations of drives, enabling users to upgrade without losing access to earlier ISO-standard MO drives.

By proving the performance of LIMDOW MO in this operating environment and by providing multiple sources of industry-standard drives and media, direct-overwrite technology is taking MO storage beyond the traditional applications into areas that require high capacity and data accessibility. By combining high-speed hardware with high-capacity media at a competitive price, MO opens the door for audio, video, multimedia, digital imaging, special effects, and animation applications.

Click here to enlarge image

To achieve Direct-OverWrite (DOW) functionality, Light Intensity Modulation (LIM) technology uses eight-layer media and two laser intensities to record data directly onto the media.

Click here to enlarge image

Click here to enlarge image

LIMDOW optical drives provide single-pass overwrite capability; conventional magneto-optical drives require a separate erase pass.

Mitch Cipriano is vice president, marketing and support, at Maxoptix Corp. in Fremont, CA.

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