| |
|
Shortcut™ Personal Audio Editor
Choosing an External Disk Drive
Shortcut firmware versions 1.3 and above support a single, external disk drive. The first fully qualified drive recommended for use on the Shortcut is the Iomega Zip drive. While other drives may be used, no others have been qualified by 360 Systems at this time. This application note discusses the possibilities for using other drives.
The external drive must be externally powered, set for SCSI ID 6 and terminated. The external drive is treated as having removable media but this is not a requirement.
The following criteria must be evaluated when qualifying a drive:
Acoustics: The drive must be quiet enough for use in the environment in which it will be installed. This is important when the drive is used near microphones during broadcasting or recording, or in critical monitoring environments.
Capacity: A capacity below 100 Megabytes is not very useful for linear recording or archiving.
Drives with capacities above 3.2 Gigabytes are not supported at this time.
Features: The drive must support the standard SCSI commands for reading, writing, starting, and testing for ready. Some drives (such as the Iomega Jaz) appear "not ready" after auto-spindown while others (such as the Zip) appear ready. Either behavior is acceptable for Shortcut. In general, drives that spin down to extend the life of the drive or the media should not be used for on-air playback due to the time required to spin-up the drive before audio begins playing.
Tape drives are not suitable for use with Short/cut.
Older drives with automatic thermal-recalibration are not desirable for use in audio recording. Drives designed for AV (audio-visual) use are a good choice as they offer high performance and freedom from thermal recalibration. Newer drives generally do not do thermal recalibration and thus the AV designation is no longer in general use.
Sector Size: The disk format must be 512 bytes per sector.
Performance: An external drive that is used for editing, playback or recording must meet certain minimum performance requirements. Transfer rates and seek times interact to affect the overall performance. Performance is not critical for external drives used only for archiving, as file copies are not constrained by the demands of real time recording and playback.
First, see if the drive qualifies as a candidate for evaluation by using the rule of thumb calculation provided below. Next, evaluate the drive in real recording, playback, and editing scenarios. Playback of edited cuts assigned to hot-keys is a good test. Audio should never drop out or skip. Recording is another good test since some drives take longer to write than read.
Throughput: 1.2 Megabytes per second, minimum
Seek time: In general, the average seek time should be less than 35 milliseconds.
Rule of thumb worst case seek time calculation:
| Seek time = (60000 / [Spindle RPM]) + (2.53 x [average seek time in milliseconds]) |
To consider a drive for qualification testing the result of this calculation should be less than 100.
EXAMPLE:
Spindle speed: 5400 RPM Average seek: 12.5 ms
Worst Case Seek time = (60000 / 5400) + (12.5 x 2.53) = 11.1 + 31.6 = 42.7
This drive is a candidate because 42.7 is less than 100 |
Reliability: Hard drives rank high in reliability. Removable media tend to have lower reliability because of the additional handling and exposure to the elements. Multiple units must be tested for weeks in playback, editing, archive, and recording scenarios to determine whether a drive is reliable enough for use in a critical, professional application. Compare drive reliability specifications to those of high quality hard drives as a starting point for choosing candidates for evaluation as an external drive.
Cable: The cable used must be designed and approved for SCSI use. The maximum length is 6 feet or 3 meters. It is suggested that the minimum length possible be used.
« back to application notes
|
|
