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DAR Sabre Hard Disk Workstation (part 3)

In doing away with the SoundStation trademark touch screen and adding a mouse, DAR have made Sabre look just a little like the type of disk editor that uses a personal computer interface...


Better than a PC?

In doing away with the SoundStation trademark touch screen and adding a mouse, DAR have made Sabre look just a little like the type of disk editor that uses a personal computer interface. But the important difference, besides the acknowledged DAR know-how in the field, is in the hardware controller. DAR comment that from the start they wanted to make control consoles that had all the right buttons ready for immediate action, so you can do something without hunting for a command. All the main functions are in front of the operator either as soft keys for segment manipulation or as hard keys for editing controls. The most important hard controls are for marking, cutting and motion control. The SoundStation controller is designed so operators can use both hands conveniently. One might think that with Sabre you need three hands since you now have the mouse to play with as well as the jog and vernier wheels, but most of the time the right hand is selecting and the left is doing many of the editing operations. DAR comment that with a PC interface, operation is not so direct. You have to worry about dragging down menus and finding the right function, or remembering key commands. They use the analogy that you would never drive a car with a mouse; it would be a little dangerous to select the brake function and then type in the level at which you would like them applied! Here, the functions are much more complicated than a car, and you need to be able to locate events with a good deal of precision. So the functions that you need are all very close by when you need to use them. When you want to manipulate the splice point, the trim, slide and crossfade controls are just an inch away. DAR believe they have an efficient, tactile and responsive approach to interfacing a person with audio editing.

The optical difference

Magnetic and optical disks are very similar in data layout. The main difference is that the mechanism that reads and writes data on the optical disk is very slow to get to any particular point on the disk. On an optical it takes around 70ms to get from one point to another where on a magnetic hard disk it takes around 10ms.

With any disk recording system, the data is initially taken into RAM and collected into sizable chunks. The data is stored as blocks because it would be inefficient to store single bytes on the disk. Because the optical disk is slower than a magnetic disk, the blocks are made larger, and clever things have been done to the sequence in which the blocks are written. One of the major software parts of the Sabre project was to rewrite the low level disk driving firmware to make it a lot smarter. That is how DAR can claim to get more channels on and off the disk simultaneously than anyone else at the moment.

As with other disk editing systems, there is a limitation on how many short segments you can ask Sabre to play in a period of time. If there are many short segments physically scattered around different parts of the disk, then the optical mechanism may not have time to retrieve them all before the playback RAM buffer is filled up. Sabre records blocks of the order of several second’s worth of audio in size, so if you were to replay lots of segments significantly shorter than a second you wouldn’t get the benefit of this long block size. DAR get around this problem by continuously looking ahead at where the data is stored on the disk and deciding the order in which to retrieve it. It doesn’t necessarily retrieve the data in the order in which it is to be played because that might involve skipping backwards and forwards across the disk when it would be better to travel in one direction gathering data which can be rearranged into the correct order later.

Even with this clever process, it is still possible, as it is with all hard disk systems, that you might ask it to perform an impossible task. The question then is, what should happen when the system’s limits have been exceeded? One answer to this might be for the system to do nothing and just play what it can, playing nothing when it can’t. But if this happened then you might not realise that a segment had been skipped and the client might ring back later to ask what happened to that important line of dialogue! Sabre can be set to work like this, or you have the option of flashing a warning up on the screen when the system realises that it is not going to be able to perform the task requested. If you think that warnings like this are not something that the client ought to see, then Sabre can also create a log which you can inspect later.

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By David Mellor Thursday January 1, 2004

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