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A word of advice

By far the best way to assess a system is to see it operating in a practical situation similar to the one in which you will be working. In reviewing nonlinear systems, it will soon become apparent that each has its own way of presenting information and on first impressions this may be a key issue. Take note of how easy it is to perform operations, how familiar the terminology used is, and whether the demonstrator is making sense or just blinding you with science. It is sometimes the case that those very familiar with a system and its terminology forget that for some people, this is all new. So ask again, and again, until the subject in question has been explained to your satisfaction.

The fairest way to judge a system is to try it out yourself. If it is not possible to review the system on your own premises, it may be possible to hire the system and have the hire fee deducted if you decide to purchase. Otherwise, arrange to take some of your usual work with you to the demonstration facility. A factor to keep in mind is who will be operating the system and if it is not only yourself, it would be a good idea to involve them as well. The supplier may even be able to arrange for you to visit a facility which already uses the system. Never be afraid to ask even the simplest question, and if in any doubt about a feature or capability, insist on seeing it demonstrated.

Assessing storage requirements
When assessing a system, it is essential to establish how much recording time will be required for your practical needs, against how much storage you can afford. As a guide, (assuming that sync words and blanking can be regenerated and added at the output, so only the active picture need be stored), then one GB of storage will hold 47 seconds of uncompressed ITU-R BT.601 4:2:2-coded standard NTSC or PAL video, and one hour requires 67GB.

With digital systems using compression, the issue is further complicated by the fact that a range of picture qualities is often available, and this will affect storage calculations. While compression has helped to make digital recording and editing affordable for a much wider market, it should be remembered that it is a compromise. In general, the higher the compression ratio, the directly proportionally more storage time per GB, but the lower the quality.

JPEG, M-JPEG, MPEG, wavelets and DCT (used for DV) are only some of the types of compression used, and different types of compression have different results. The compression ratio or data rate alone cannot be used as a definition of the resultant picture quality. This may depend on the algorithms used, the implementation, and the nature of the source material.

For ease of comparison and to establish how much recording time is provided by a given system configuration, suppliers of editing systems were asked to give recording times per GB, and these can be found under 'Storage'. An idea of total recording times can then be calculated by the capacity and maximum number of drives supported. It should be noted however, that although a system may support large amounts of storage in total, there may be a limit to how long an individual recording or clip can be. Any such limitation is also indicated under 'Storage'.

For systems using compression, times were given for their highest, standard and lowest picture qualities. Although helpful, these times are only a rough guide, since they may vary according to the nature of the video signal being recorded.

In addition, while suppliers have been asked to provide their estimates of equivalent conventional qualities for given levels of compression, these estimates are only intended to be helpful guides and are essentially subjective. Knowledge of which compression level to use for adequate picture quality against storage time for a particular system can only be gained through experience.

While the amount of storage space required can be reduced by using high compression ratios, in many instances it may be necessary to use lower ratios in order to have sufficient quality for complex or fine editing. Therefore, depending on your requirements, it may be helpful if the system allows different picture qualities to be sequenced in the same programme. If a system supports this capability, it may be mentioned under 'Playback'. Alternatively, look under 'Picture Editing/Effects' to see if a system allows transitions to be made between clips of different qualities.

An often unavoidable method for reducing the amount of storage required is to be selective about which material is recorded into the system in the first place. Some systems allow recording on the fly, or naming of shots while recording, and many can use prepared lists for automatic 'batch' recording of selected shots. Batch recording and details on importing logs/shotlists are covered under 'Ingest'.

Some manufacturers also supply cut-down systems for digitising only, thereby eliminating the need to tie up more expensive editing systems with the logging/acquisition process. Whether or not digitising-only systems are available is outlined under 'Hardware'.

Another method of effectively reducing the amount of disk space required is to digitise rushes/dailies using a low quality, perform a rough edit and then redigitise (or auto-assemble) only the required material back into the system at a high quality. Details on selective re-recording capabilities and external machine control can be found under 'Synchronisation/Machine Control'.

If multiple versions of a programme or stock shots are required, it may be useful if material can be shared between projects, thus avoiding the need to use valuable time and disk space for duplicating material. Whether or not a system allows material to be shared between projects is outlined under 'Library' (and again, it may be useful in such cases if the system allows different picture qualities to be sequenced in the same programme).

Finally, even if calculations have been made beforehand as to how to maximise disk space, there will often be unforeseen instances where additional material must be brought into the system at the last minute. In such cases, especially where the disk is getting full, it is useful to have a feature which easily allows the deletion of unwanted material in order to make room for the new recording. Most systems support such a (consolidate) feature, but it is worth checking how effective or selective the implementation is in practice.

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