Removable cartridge hard drives, such as the Iomega Jaz shown here, are suitable not only for general backup, but for direct recording of up to about eight tracks.
No‑one enjoys making backups, but they are a necessary part of digital audio recording. Martin Walker explores the options, and explains their strengths and weaknesses.
As digital audio recording becomes increasingly commonplace, the problems of backup become ever greater. No longer can we save a quick extra copy of our files on to a floppy disk and stick it in a drawer in case anything on our hard drive gets corrupted or accidentally deleted. For a start, with audio files sizing up at 5Mb per minute (with a 44.1kHz mono signal), a five‑minute stereo track would span 37 floppy disks, which just isn't a practical proposition. Another worry is that often the files tend not to be backups at all — despite the huge increases in the size of hard drives, digital audio will eventually fill them up, so many people mistakenly use the term 'backup' when moving files to another medium for archiving, rather than making an additional safety copy on a daily or weekly basis (the traditional form of backing up).
Computer professionals don't consider a file safe unless it exists in two places. Although it is fairly common to keep only a single copy of analogue master tapes, digital is much less forgiving if anything goes wrong. A tiny dropout on an analogue tape may give a short click on playback which can be neatly edited, and probably not cause too many headaches. On the other hand, digital information may be fragmented and scattered to the four corners (so to speak) of the hard drive. Even a single corrupted byte may result in a portion of a track being lost without trace, or even worse, the entire track not being recognised by your software at all. Backups are vital.
Even when we recognise the importance of backups, it can be a confusing experience trying to decide on the best way to store them. There is a huge variety of backup devices on the market, with new ones appearing all the time. On the other hand, many people who have been faithfully backing up for years are finding that this rapid advance in technology causes a different problem — the almost inevitable obsolescence of some older drives. What happens is that first the drives become difficult to source, and then, slowly but surely, it becomes more difficult to find anyone still stocking the media. I recently received a call from a musician who had built up a multi‑Gigabyte sample library using an old Sony optical drive. After a scare when his drive refused to read the library, he managed to buy another one second‑hand, but sensibly wanted to transfer his library to another, more modern medium before disaster struck again.
Narrowing It Down
There are two main types of backup, random and linear access. Random access is exactly what we have on hard drives — you can load any file you like from anywhere on the drive. Linear systems such as DAT and ADAT, by contrast, store data in a long stream, and if you need to access the final track, you need to fast forward through the rest of the tape to get to it. For backup purposes the type you choose depends entirely on how you work. If the backups are mainly for archive purposes, so that you have a copy of every project you have worked on, linear storage is fine. It may take a bit longer to find and load in exactly the information you need, but it will be considerably cheaper in the long run when lots of data storage is required.
Random access storage is more useful if you need to grab tracks quickly and regularly, and tends to be similar to working with a hard drive — in fact, removable hard drives are one of the options available. If you have a commercial studio, random access may be the best solution, especially if you are juggling many regular clients with lots of smaller projects. You can also bypass the backup stage altogether (although this is not advisable) by using removable hard drives that are fast enough to become your main storage medium (more on these on the next page). Although once again this tends to push up the cost, turn‑round time drops from minutes, to transfer data from your backup to the fast main drive, to seconds, as you simply swap cartridges and carry on with the next project. You could of course combine the two approaches, and archive every project as well, just keeping enough removable cartridges to cope with current projects.
Even a single corrupted byte may result in a portion of a track being lost without trace, or even worse, the entire track not being recognised by your software at all. Backups are vital.
Your choice may be determined by external factors, such as compatibility with other musicians and studios, or because you need to supply masters in a particular format such as CD‑R or Exabyte tape for glass mastering and subsequent duplication. You may even be swayed by physical considerations — some people are still worried that the small size of DAT backup tapes makes them more likely to get lost, and may feel happier with something physically larger.
For long‑term archiving of completed projects, your choice of media may also be determined by its claimed longevity. New products will have a projected shelf life of some years, but little data to support the figure apart from some accelerated ageing tests. Some of the more traditional tape backup cartridges have been in regular use for years, and have proved their reliability over this long period. Anybody with paying clients will obviously have to bear this in mind, as they are likely to amass a large amount of invaluable data.
Removable Hard Drives
Many professional hard disk recording systems (such as SADiE and Soundscape) come with a choice of hard drives fitted in removable bays. You can work with a variety of drives of different capacity, and given that each will probably hold a single project, changing between them is simply a matter of hot‑swapping the drive, which takes only a few seconds.
Glyph's removable Jaz drive.Removable drives offer the easiest way to work, but of course you have to buy a new hard drive for each project, which makes it very expensive — some form of extra archiving would be preferable for most people. A cheaper solution is to use a specially designed hard drive that has removable cartridges. The core of the drive assembly remains, but the actual magnetic disks are contained within a plug‑in casing, and can be swapped freely. This makes the media a lot cheaper. Many musicians have been using Syquest 44Mb and 88Mb drives for sample storage for years, but the maximum capacity of such removable drives has steadily increased, and now it is possible to buy them in sizes of 2Gb or more. Until recently their speed was also considerably slower than fixed hard drives, which made them difficult to recommend for the actual recording process. However, recent drives such as the Iomega Jaz (with 1Gb and a newer 2Gb capacity) and the Syquest SyJet (1.5Gb) are perfectly usable for eight‑track recording, although many people still prefer to work with a project's worth of data on a faster fixed hard drive in their computer, and then regularly backup the entire project to a single removable cartridge.
At a more humble level, the ubiquitous Iomega Zip drive, despite holding only 100Mb, is widely accepted as a standard for storing samples, graphic data, and general backups of files. It is also beginning to appear in place of the floppy disk drive on some computers, since the floppy is woefully inadequate for most of today's storage requirements.
Removable‑cartridge drives can be bought as internal EIDE or parallel port external devices for PC use, but most musicians will prefer to buy the SCSI versions, since these will not only work with Mac or PC, but can also be pressed into service with the vast majority of samplers as well (with a differently formatted cartridge).
The Glyph Technologies range includes combination racks, which can hold any of the tape formats mentioned, as well as fixed and removable hard drives, and CD‑R and CD‑RW drives.
Optical Storage
Any device which uses a laser for writing and reading is termed optical, and there are two main types. MO (Magneto‑optical) drives have been available in various forms for some time, and the medium is normally a 3.5‑inch cartridge holding 650Mb of data. These are very reliable, but are slow to use, since writing data requires two passes — the first to make the surface writable, and the second to actually write the data.
The other main type uses phase‑change technology, and include CD‑R and CD‑RW discs (see next section), as well as the latest type of MO drive, termed LIMDOW (Light Intensity Modulation Direct OverWrite). LIMDOW drives have the advantage over standard MO drives of performing both preparation and writing operations in a single pass, as well as being compatible with the older MO cartridges, and providing much larger storage capacity (up to 2.6Gb). Not surprisingly, LIMDOW drives don't come cheap, and models tend to start at around the £1300 mark, but the media makes up for this, working out about 3p per Megabyte. With a claimed 30‑year shelf life, they are also ideal for long‑term archiving purposes.
One rather more specialised MO drive is the Sony Minidisc, the 140Mb capacity of which is rendered rather more palatable for audio use by the ATRAC compression system, which compresses audio by 5:1 to squeeze 74 minutes of mono audio on to each disc (see the 'Data Compression' box). Other phase‑change drives include the PD from Panasonic, which combines 650Mb optical storage capability with a standard 8‑speed CD‑ROM player in one neat package at about £300. This has been available for some years, and still has one main advantage: its speed is typically double that of the newer CD‑RW drives.
Overall, MO drives are ideal where fast random access is required (the fastest LIMDOW drives can run 5 or 6 times the speed of CD‑RW), and where large amounts of storage are needed, since the low cost of the media will then help to make the initial high price of the drive seem more acceptable.
Compact Disc
'Burning a CD' is becoming a common thing for musicians these days. It's not hard to see why, with the cost of suitable equipment plummeting along with the cost of blank media. CD‑R (Recordable) and CD‑RW (Re‑Writable) drives are both examples of optical technology, and the information stored on the CD is normally one of two types — CD audio or CD‑ROM data.
A five‑minute stereo track would span 37 floppy disks, which just isn't a practical proposition.
Audio CDs are, in data terms, quite restricted — they contain a number of tracks of 16‑bit/44.1kHz stereo audio. Burning Audio CDs is ideal when handing out in‑progress discs to studio clients, and for pre‑mastering (where the final version of an album is prepared, complete with any fades and other tweaks, to later produce a glass master for CD duplication). You could also burn audio CDs for stereo track archiving, with the proviso that not all CD‑ROM drives can digitally extract this audio perfectly (sometimes there may be a few slight glitches, depending on the drive model, although this can normally be overcome with special software). For most people, archiving to audio CD will present few problems, but having the only copy of an entire album on an audio CD might be tempting providence.
CD‑R and CD‑RW recorders, like the Yamaha CRW4260 shown here, are ideal for running off in‑progress copies of projects, as well as for longer‑term storage.For backups and archiving, the CD‑ROM data format is preferable. This uses a file‑based structure just like a hard disk, and has more rigorous error correction to ensure that every byte can be re‑read exactly the same every time. If you want to back up a set of WAV or AIFF files, then you will need the CD‑ROM data format. Unlike audio CDs, data CDs are not restricted to 16‑bit/44.1kHz stereo, and allow you to backup any format of sound file, from 8‑bit mono files through to 24‑bit/96kHz multitrack recordings. It is even possible to make backups from SCSI hard drives or CD‑ROMs which use formats normally unreadable by the host computer, which is ideal if you have a large sample library, as you can create image files of your sample hard drive cartridges, and then burn CD‑ROMs from them for posterity.
Computer professionals don't consider a file safe unless it exists in two places.
Stand‑alone CD recorders are the easiest way to burn Audio CDs, although they are not suitable for backing up computer data.The equipment used to burn CDs falls into two main categories, stand‑alone and computer‑based. Consumer stand‑alone recorders (like the Philips CDR870 reviewed in the December '97 issue of SOS) are ideal for audio CD, and are quick and easy to use. The going price seems to be about £500, and for this you get a complete package — you feed in a digital signal from a DAT tape, or the digital output from another CD player, and an audio CD is created in real time from the incoming data. Low‑cost recorders like this use special 'consumer' CD blanks, which are more expensive than the ones used in higher‑priced professional stand‑alone recorders like the CDR800 from HHB, and the CDR200 from Fostex, both at about £1500. However, entry‑level professional models such as the Marantz CDR630 (at about £750) are starting to appear. Stand‑alone recorders are ideal in the studio for running off audio CDs, but normally won't back up data files, and only burn at single (real‑time) speed — a one‑hour album will always take an hour to burn.
If you already have a computer, adding a CD‑R or CD‑RW recorder is a considerably cheaper option (starting at about £200 to £300), and the latest models will burn at 4x speed. This is a major timesaver, and even makes small duplication runs feasible. Of course, you have all the potential problems associated with using computers (especially PCs), but once you get past the inevitable hiccups of your first few burns, things normally run fairly smoothly.
CD blanks can now be bought at under a pound each in 100+ quantities (with the consumer versions costing about double the price), while CD‑RW discs are about £13 each, dropping to £10 in quantities greater than 20. One thing to watch out for here is that although re‑usable CD‑RW discs are an attractive proposition, they can only be read by CD‑R and CD‑RW drives, and a very few recent CD players. The chances are that your hi‑fi CD player won't touch them with a bargepole.
Tape Drives
Many musicians already have a tape drive for audio backup — the ubiquitous DAT recorder. As long as it has suitable digital I/O sockets, and you also have a soundcard with a pair of sockets of the same persuasion, you can store and restore audio files using your digital recording software. What they can't do is back up computer data files, nor multitrack audio data (unless you save as a set of stereo files). For these you can use a variety of tape drives.
One of the most common tape formats for general backup is the Travan mini‑cartridges, developed by the 3M company. A 4Gb cartridge (which for computer data will normally store about 8Gb of compressed data) costs about £20, and the drives can cost as little as £300, making them very cost‑effective.
There are special computer DAT drives for backup purposes, using a 4mm tape format known as DDS (Digital Data Storage). These are very reliable, but rather more expensive, and the special computer‑grade DAT tapes are also considerably more expensive than audio ones (although they do store a huge amount of data). Various models are available using mechanisms from manufacturers including Sony and Hewlett‑Packard. Models using the DDS2 format can store 4Gb of uncompressed data (up to 8Gb compressed) on a single tape, and 12Gb (24Gb compressed) on a single DDS3 tape (at about £25 each). Drives start from about £500, but transfer rates are quite fast for tape, at 60 to 120Mb per minute (4 to 8Gb per hour).
One of the best known manufacturers of tape drives in the audio world is Exabyte, who make quarter‑inch cartridge (Travan) drives, 4mm (DAT) drives, and also a larger 8mm tape which is very similar to the Video 8 format, found in drives such as the Eliant 820, which can store 7Gb of uncompressed data (up to 14Gb compressed). For huge storage requirements, drives like the Quantum DLT‑4000 use half‑inch cartridge streaming technology to store a massive 20Gb uncompressed (40Gb compressed) at a transfer rate of 1.5 to 3Mb per second.
Summary
You don't need to visit a specialist computer supplier for most of these backup solutions — many specialist music dealers stock them, either as internal drives for mounting directly into your computer, as SCSI desktop units, or purpose‑built rackmounting units, complete with shock absorbers to stand life on the road if necessary. If you have large storage requirements, it is always best to consult a specialist dealer, since they provide suitable technical backup in emergencies, which you may not get if buying discount from a computer warehouse. Suitable product families include Glyph Technologies (from the Global Distribution Group) and Rorke Data (available through Music Lab).
The future is always round the corner, but once we turn that corner yet another one appears, so we will always be tempted with new technologies. DVD‑RAM is the long‑anticipated optical solution to storage problems, with random access, fast transfer rates, and a possible data capacity of 17Gb. However, several generations of these are already planned, and as usual there will be compatibility problems between them. There are also several new standards for higher‑bandwidth audio, including SACD (Super Audio CD), DAD (Digital Audio Disc), and DVD Audio. Somehow, I think that backup may get quicker and cheaper, but maybe not as fast as we increase our storage requirements. Some things never change!
Data Compression
When attempting to cram the maximum amount of audio on to any type of backup medium, data compression may be an option. There are two types: lossless and lossy. With lossless compression, every byte of data remains intact, but various methods are used to make file lengths smaller. At its simplest, a string of identical bytes could be replaced by the value of the byte, and the number of identical bytes to follow, but modern algorithms also use a variety of very clever techniques to massage the data into a smaller package that can be later restored to an identical larger file.
Lossy compression can result in much smaller files, but at the expense of losing some of the data. While this initially sounds like a non‑starter, in many situations it is possible to lose a lot of information before any appreciable difference is noticed. Video image files in particular can be compressed by a huge amount with only marginal degradation being visible in most cases — a typical 50k compressed JPEG picture may expand to 2.5Mb or more when you open it in a graphics package.
Over the last few years much work has been done in improving lossy compression for audio, using techniques such as masking (where high level at one frequency masks lower levels at nearby ones). The Sony Minidisc format achieves 5:1 compression with minimal sound degradation, using its latest ATRAC (Adaptive Transform Acoustic Coding) algorithms. For sound archiving, MPEG layer III (MP3 files) can compress audio a lot (typically 12:1) while still maintaining good quality. Even more compression has to be achieved to manage real‑time streaming of audio over the Internet, and many competing technologies are available.
For archiving audio data, most people will need lossless compression, and it must be said that whatever the method, the huge file sizes involved will normally mean that it is likely to take an appreciable time to carry out. Sadly, audio doesn't compress very readily using lossless techniques, since it rarely contains much repeated data. I tried using a zip‑based PC compression utility to zip up a few audio files on my hard drive: a 1kHz test tone was compressed by a huge 99 percent (from 862k to 9k — plenty of repeated data here), a drum loop dropped by 35 percent (still well worth having), but a piece of stereo rock music only dropped by 5 percent. You get the idea — the result is largely dependent on the material, although Emagic include the Mac‑based ZAP (Zero‑loss Audio Packer) utility with Logic Audio, which has been specially optimised to compress audio data.
Going A Bit Soft
Apart from stand‑alone CD‑R recorders, most other backup drives will not work without suitable software. Many of the drives mentioned here are available as standard SCSI devices, in which case they will simply appear to your computer as another connected device, so that any file can be stored or retrieved from them. However, specialised backup software can make the process easier, by enabling you to compress the data as it is being saved. In the case of large backups of several Gigabytes, this not only enables far more data to be crammed onto each piece of media, but can significantly reduce the time it takes (by up to half in some cases).
Always make sure that suitable software for your computer is supplied with a drive, since generic backup software may not recognise a particular drive. This is also the reason why non‑standard drives and interfaces can rarely be pressed into service for backup. Using Audio DAT recorders for computer data backup, or connecting them to USB or parallel port printer sockets, is sadly a non‑starter.
Track Minutes Available On Standard Media
The length of audio data that can be crammed on to a single disk, cartridge, or tape depends entirely on the number of (mono) tracks used. Because of this, the easiest way to provide figures is in track‑minutes, assuming the fairly standard sample rate of 44.1kHz.
- For 16‑bit audio at 44.1kHz, a track‑minute will occupy about 5Mb.
- The higher sample rate of 96kHz will use double this.
- 24‑bit files will take 1.5 times as much space as 16‑bit ones.
- So, for those who aspire to 96kHz/24‑bit recording, do bear in mind that your total storage requirements will be three times more than those of 44.1kHz/16‑bit.
Hard drives (whether fixed, removable, or cartridge‑based) are available in a huge variety of capacities. The humble Zip drive holds 100Mb (20 track‑minutes) and so could manage a 10 minute stereo track, or five minutes of four‑track data. The Iomega Jaz drive holds 1Gb, which equates to 200 track‑minutes (25 minutes of eight‑track data), but a new 2Gb model is now available which would hold an entire album's worth of eight‑track.
CD‑R and CD‑RW disc capacities are more confusing than you would think. Although audio CDs can store up to 74 minutes of stereo music (148 track‑minutes), when storing the same files as computer data, a more rigorous error correction is used which takes extra space on the disk, resulting in 650Mb of storage space (130 track minutes). CD‑RW disks hold the same amount, except if you opt to use the latest packet‑writing software with drives that support this. In this case, only 493Mb of storage is available (98 track‑minutes — see the May '98 PC Notes for more details).
Tape cartridges are normally available in various lengths, but one specific area to watch out for is their claimed capacity — this is normally quoted on the basis of a typical compression value of 2:1. Since audio is unlikely to achieve such values, the amount of data you can cram onto each tape may be significantly less than the quoted value. Bear this in mind when choosing backup media sizes.