Optical Disk & CD-ROM

There's a revolution taking place and it's heading your way! David Mellor explains the increasing importance to musicians of optical technology for data storage.

The past two digital revolutions were pretty exciting — digital stereo on DAT gave musicians the kind of sound quality that could previously only be approached by an expensive analogue recorder with Dolby noise reduction (a combination that once cost the best part of £10,000), while digital multitracks like the ADAT and DTRS formats represented further spectacular leaps towards making pro standard audio affordable to 'ordinary' musicians.

The current digital revolution, as any regular reader of SOS will be aware, is in hard disk recording, where units like the Akai DR8, Vestax HDR6 and Fostex DMT8 bring multitrack hard disk recording down to the kind of price that was once mere fantasy. But we still have a lot to learn about how hard disk systems should be used to best advantage.

In the top professional bracket, hard disk recorders are used mainly for post‑production (adding audio to pictures), and for that they are ideally suited. Typically, clients will bring their tapes into the studio where they will be transferred to the fixed hard disk of whatever tapeless recording system the studio happens to own (AudioFile, SADiE, Pro Tools, etc). When the session is completed, the audio will be copied back to tape and the hard disk erased, in readiness for the next client/session.

Hard disks are very good for the quick turnaround nature of the post‑production business. What they are not quite so appropriate for is music recording. Not because of any limitations in the sound quality that any well designed system will offer, and certainly not because of any lack of facilities, but music recording projects are much more likely to take place over a longer timescale, and the project may not run continuously from initial track laying to final mixdown. In the home or project studio, this is very significant. Whereas full‑time professionals may start a project and work on it until it is finished, many of us have to juggle our tasks and work on several projects, or several parts of the same project, at the same time. I don't know whether I qualify as an 'average' project studio owner, but I usually have three CDs worth of material on the go at any one time, and I can spend more than a year working on a single project. If I owned an 8‑track hard disk system, I would need at least 12 gigabytes (12,000 megabytes!) of storage to handle all of this, possibly more.

The answer to the storage problem, I feel, will ultimately be removable optical storage, where you can treat the disk medium just as you do tape. When one disk is full, simply swap it for a new one, and buy as many disks as you need for the work you are doing. We haven't heard a great deal about optical disks in the pages of Sound On Sound yet, mainly because they haven't been entirely suitable for audio purposes. But now we are on the threshold of the point where optical disks will indeed be very suitable, and I imagine that companies producing digital tape and hard disk products today will be producing optical disk products next year or the year after. I predict that in the fairly near future we will be recording multitrack and stereo audio onto optical disks, and we will be sending our demos to record companies on CDs that we have made ourselves in our home and project studios. With this in mind, let's look at the state of play in the optical disk and CD‑R (as recordable CDs are often known) market right now; later on I will speculate on what may be around the corner...

Optical Disks

As yet there is no such thing as an optical disk recorder (at least not in any sub‑stratospheric price bracket), but there are hard disk recorders that you can attach an optical disk drive to. Most computer‑based hard disk recorders will treat an optical disk drive just as though it is a hard disk. There are a number of such systems available, but I will refer to two examples with which I am personally acquainted. The first is my trusty Apple Macintosh Quadra 650 (superseded by Power Macs maybe, but I'm still not selling it!) fitted with Digidesign's Audiomedia II card, and running MOTU's Digital Performer software. The second is the remarkable Akai DR8, which I reviewed in SOS August '95. Digital Performer is the audio recording version of Mark Of The Unicorn's Performer MIDI sequencing software. It is compatible with a number of Macintosh hard disk recording systems, including Digidesign's Session 8 and Pro Tools. Many of my comments on Digital Performer and its associated hardware will apply to other Mac and PC hard disk recording systems too, since the same physical limitations apply.

In some respects, hard disk and optical disk drives are quite similar. Both are available with SCSI connectors that you connect to the computer or hard disk recorder, and both have to be formatted so that data can be stored. There are two main differences between hard disks and optical disks. The first is obviously that optical disks come in removable cartridges. Hard disks sometimes do, but large capacity disks are far too expensive to treat like you would ADAT tapes. An optical disk capable of storing around two hours of stereo audio, or the equivalent in multitrack, costs about £60, which is rather more than DAT but not totally out of this world.

The second difference between hard disks and optical disks is that the hard disk works by magnetising the surface of the disk in a pattern of ones and zeros that describe the digital audio signal. Even when you record multitrack audio, the hard disk doesn't actually record separate tracks. Conventional hard disks can only deal with one stream of data, so the disk has to record a little bit of track 1, a little bit of track 2, and so on. To record and replay several tracks simultaneously, the drive head needs to retrieve data for all the tracks sequentially and very quickly, so that the system can once again reconstruct the data into exactly synchronised tracks. Obviously, in order to do this the head has to be able to move about the disk very quickly, to access the data, and when the data starts to flow, it has to flow very quickly too. Magnetic hard disks are very well suited to this, because the heads are very small and lightweight. Optical disks, on the other hand, work by heating small areas with a laser and exposing them to a magnetic field. On playback, the laser bounces light off the disk and a sensor detects the angle at which it bounces. The mechanism necessary to do all this is bulky and heavy in comparison with the hard disk, therefore the access time to any part of the data is slow, and the rate of data throughput is less. Also, a separate erase cycle is needed, so recording takes twice as much effort as playback.

The upshot of all this is that where it is pretty straightforward to record and replay any combination of eight tracks on a modern hard disk, you cannot expect this level of performance from an optical disk. The best you will achieve from an optical disk connected to an Akai DR8, for example, is 8‑track replay, or 7‑track replay and 1‑track record. You can't obtain 6‑track replay and 2‑track record, since even the fastest currently available optical disk drive is too slow. Note that it is not the DR8 that is too slow, it's the disk.

Another problem appears when you start to edit the audio. As you know, instant access and ease of editing are the reasons why we have disk recorders in the first place. When you record audio onto the disk, it will be laid onto the disk more‑or‑less in sequence, almost like tape (assuming you started with a blank, defragmented disk). When you play it back, the optical pickup will never have very far to go to find the next section of data that it needs. But what happens when you start to restructure the audio? Suppose that the second line of the first chorus was a bit shaky and you want to replace it with the same line from another chorus? How about moving the solo so that it comes later in the song? What about adding another track? Now the data to be played is no longer sequential or contiguous and the head must skip quickly across the surface of the disk to retrieve all the required sections.

Figure 1 shows a 'worst case' scenario that served to test the three optical disk drives mentioned later in this article. I recorded about five minutes of stereo audio onto a disk using Digital Performer, then cut out segments from various points and arranged them into a short sequence. I started off with 2‑second segments of audio, which I found I could place back‑to‑back on four tracks, filling all the available space on the screen, and it would play back perfectly (using the maximum buffer size on the Digidesign Digital Audio Engine software, upon which Digital Performer relies). I tried the same thing with 0.25‑second segments and found this to be the best I could achieve. If I placed the segments any closer than this, then playback would stop. You may think this is pretty extreme, and it is, even though it is only on four tracks. But this kind of edit density only has to occur once in a song and you will have a problem. Other disk recording software is available that can perform crossfading between segments, which may create literally hundreds of very short segments scattered across the disk. The number of tracks, segment length, and edit density are the limiting factors in all disk recording, but especially so with optical disks.

Driving Ambitions

I tested three optical disk drives with my Quadra 650 computer and the Akai DR8, all of which can be obtained for around the same price if you shop carefully. These were the Maxoptix Tahiti‑T3, the Pinnacle Sierra, and a d2 électronique SMO 1300. One thing you have to note is that the brand name of the box is not necessarily the brand name of the drive inside, so you will need to develop some skill in drive‑spotting to make sure you get the one you want at the best price. All three drives take 1.3 gigabyte cartridges, which equates to 650 megabytes per side (as yet, there are no drives that can play both sides simultaneously) — good for around an hour of stereo recording, or 15 minutes of 8‑track. Smaller capacity drives are also available, though these are probably better suited to sample storage than disk recording.

In the end, the choice of drive comes down to raw speed and I certainly found that one drive was faster than the other two, and therefore simply better. I have to stress that in this industry, whoever is leader today may be an also‑ran tomorrow, so don't apply the conclusions I come to here to the next wave of products these companies will produce — they are all in hot contention.

Although I am still using the d2 électronique SMO 1300 quite happily for 4‑track recording, and I am confident that it is a high quality product, I have to say that it was the slowest of the three. My measurements showed that it had an average seek time (the time it takes the head to get to the data) of 38.9 milliseconds and a sustained read rate of 1546 kilobytes per second. This compares with the Maxoptix, which had a seek time of 19.4ms and a sustained read rate of 1533 kilobytes/s. The slightly lower data throughput of the Maxoptix (which is approximately halved for recording) didn't seem to represent as much of a problem as the differences in seek time and access time. Although both drives are suitable for 4‑track recording work, only the Maxoptix is workable for 8‑track, and then only just with the Akai DR8. It takes top disk recording manufacturers like Digital Audio Research to get the Maxoptix Tahiti‑T3 to work to its full potential, which shows that optical disks haven't yet really matured as a technology. The Pinnacle Sierra unfortunately didn't respond to my disk testing software, so I don't have any test figures, but it worked fine apart from that and was very nearly up to the Tahiti‑T3's standard. In conclusion, all three drives are recommended, but the Maxoptix Tahiti‑T3 is more recommended than the others!

Recordable CD

Recordable CD (usually referred to as CD‑R) has been with us for some time now in the form of CD recorders, which are in appearance just another type of audio device. My first experience of CD‑R recorders (some time ago) was not a happy one, since I found that the possibility for operator error was huge, with a corresponding cost in time and CD‑R blanks. These days, CD recorders have now been refined to a point where they are certainly useful, but are still not at the 'must have' level. On the other hand, if you are editing audio on a computer, you can attach a CD‑ROM writer which will give you the ability to create normal CD‑ROMs from your data and create audio CDs too, very easily. I tested two units, the JVC RomMaker and the Pinnacle RCD, both of which gave excellent results. Both units are SCSI devices, so I was able to connect them very easily to my Mac. The JVC actually incorporates a hard disk as well, so it needs two SCSI addresses; something you may need to consider if your SCSI buss is approaching the limit of its capacity.

Once again, CD‑ROM writers are at the useful but 'not quite there yet' stage of development and much depends on the software that is supplied with the device. I used JVC's and Pinnacle's own software, although other manufacturers' software to do a similar job is available at extra cost. Although CD‑ROMs are undoubtedly interesting, let me concentrate on audio CDs.

To create an audio CD, first of all you need a stock of CD‑R blanks. These cost around £8 or so each and are available in 63 and 74 minute sizes. Some CD‑R blanks are advertised specifically as an audio product, but there doesn't seem to be any difference in their suitability for recording audio. I tried three brands and I couldn't detect any difference among them (but only time will tell how long they retain their data successfully).

Since CD‑Rs are non‑erasable, you have to make absolutely sure that your audio file is perfect. The only 'going back' is going back to the shop to buy some more blanks! On a Mac, you will probably prepare your audio in Sound Designer format, since that is just about the standard in the professional (Mac‑based) audio world, although AIFF is supported too. If you were using a PC, then .WAV would be your format. You don't need to sequence the whole CD into one gigantic file, as each track on the CD will be created from one file on your computer. JVC supplied me with two types of CD writing software, one of which (Personal Archiver) turned out to be virtually useless for audio CDs, but their RomMaker software (Figure 2) worked well once I had figured it out. In truth, the only problem I had was that the manual writers assumed that anyone using a JVC RomMaker system would be making CD‑ROMs, with audio as an afterthought (silly me for having audio as my only thought). Most of you will have come across mixed mode CDs already, where track 1 is a data track for use on a PC or Mac and the rest of the tracks are audio. To RomMaker, every CD is a mixed mode CD, but you can omit the data track if you wish. Once I had grasped that idea almost everything was fine, and I simply loaded the files I wanted into the RomMaker window and set the gaps between tracks.

The next step is to transfer all the files to the RomMaker's internal hard disk. The reason for doing this is that writing to a CD‑R has to be a continuous process and any interruption in the data stream will mean a ruined CD‑R blank. Unless you are sure that your hard disk is fast enough, that it won't suddenly recalibrate itself in the middle of a transfer, and your files are not fragmented, then writing to the unit's local disk is the perfect way of working. Transferring the files takes as long as any disk‑to‑disk copy would, but once the material is on the RomMaker's hard disk, then copying to the CD‑R can be done at 2x real‑time speed (some CD‑ROM writers can do 4x speed, or a quarter of real time; Yamaha's CDE100 for example). I recorded about 20 audio CDs on the JVC RomWriter and all were perfect, so I can thoroughly recommend it.

Of course, no relatively new technology is without its problems or limitations, and I found two:

• Firstly, although the JVC RomMaker is excellent for producing batches of identical CDs, it completely ties up the computer while it is copying from its own hard disk to the CD‑R blank. I would have thought that this could have been done internally, rather than via the computer's SCSI buss. An opportunity missed, I'd say.
• The second problem is obviously due to a software bug. In a mixed mode CD there is a mandatory two second gap between the data section and the first audio track. Unfortunately, if there is no data track then the RomMaker software insists that there must be a gap between track 1 and track 2. Any of the other tracks can have no gap or a gap of any duration. This gap problem was the reason why I found the more basic Personal Archiver software unusable. It only allows a fixed gap of up to two seconds (see later). To a computer system designer, it may seem 'obvious' that all tracks on all CDs should be separated by two second gaps, but it certainly isn't obvious to a musician like me who wants to include segues and crossfades between audio tracks; these are ruled out completely.

The second CD‑ROM writer I tried was the Pinnacle RCD (shown in Figure 3). This worked as well as the JVC RomMaker, even without an internal hard disk. Of course, this meant that I now had to source all my audio material from a fast, reliable hard disk, so I was lucky to have a 1.7 gigabyte Micropolis AV disk available for the purpose. One slight problem was that the Pinnacle software only lets you have the same duration of gap between all tracks, and only up to two seconds. This is not really adequate, but at least you have the option of setting no gap at all. The way around this is to include the gap as a silent period at the end of each audio file. No problem.

The only slight difficulties with the Pinnacle RCD were that the supplied software isn't suitable for creating identical batches of CDs, since it cancels your carefully created track list once the CD is made! Also, I found that on occasion there was a very slight click right at the end of the CD. I couldn't trace why this was so, whether it was the CD‑ROM writer, the RCD software, or my software or computer, but it didn't happen with the JVC RomMaker.

What's Next?

What's next in the optical disk world is a 2.6 gigabyte drive and cartridge. Several manufacturers are working on a standard that will store 1.3 gigabytes, roughly equivalent to two hours of stereo audio or half an hour of 8‑track recording per side. Since the disk won't physically be any bigger, access to the more tightly packed data should be faster and so 8‑track recording should be possible with these drives, according to what I have heard on the grapevine. When they appear, optical disk recording should become totally practical, with no drawbacks other than the fact that the cost of the cartridge will still be much higher than tape.

As far as CD‑ROM writers are concerned, I don't have such good information on what might happen, but I can speculate that since CD‑ROM writers have only just begun to make a significant penetration into the computer market, then as the manufacturers achieve a greater volume of sales in that market, prices for everyone (including audio users) will be set to tumble. But as always, if you think you can profit now from making your own CDs, then now is the right time to buy, since these units certainly do the job.

Thanks to all companies concerned for making their products available for test."Since CD‑Rs are non‑erasable, you have to make absolutely sure that your audio file is perfect. The only 'going back' is going back to the shop to buy some more blanks!"