With more and more members moving to computer-based editing, David Jackson discusses Non-Linear Sound.

The Director and I had been editing her latest drama production, which was shot in Suffolk last October. This was her first close look at non-linear editing (NLE) on a PC and, quite apart from the precision of editing possible with the new technology, she was most struck by the ability to manipulate the sound track with equal precision. So, for those who are still using linear editing techniques, I thought you might like to hear about this under-publicised facet of NLE.

We used Premiere 5.1, then the latest version of Adobe's timeline editing program. Other NLE software may offer similar facilities, but is likely to differ markedly in detail. As always, you must study the small print to see what subtleties there are in any software suite.

The first thing that linear editors notice with NLE is the ability to cut sound with incredible precision to eliminate little imperfections like ums, errs, unwanted noises off (as long as they don't overlap anything else that must be retained) and even bits of unwanted dialogue (assuming the speaker's face isn't too visible at the time. And, having made a hole in the audio track, the ease with which a small section of ambience (background 'silence') can be pasted over the gap is the final element to convince a doubter.

But getting rid of imperfections is only part of the soundtrack story. Adding in extra elements of audio, all in CD-quality stereo, is another very simple operation. Timing can readily be adjusted, if necessary by trial and error, until the effect is just right. And each element of the soundtrack can be individually adjusted for volume and other characteristics almost frame by frame, so any mismatches can be easily overcome. Not only that, but it is very easy to cross fade from one clip's sound to the next, extending the clip's sound beyond the end of the associated pictures as required, to effect a smooth aural transition from one scene to the next.

And then there are the filters. Premiere 5.1 introduces a whole range of audio filters which previously were only available by buying a separate sound program. Perhaps the most useful in everyday editing are those which deal with unwanted hums and hisses. Mains hum can be surgically removed using the notch filter and selecting 50Hz for UK mains. This filter removes frequencies close to 50Hz and nothing else, so there is little or no effect on the wanted element of the sound.

For broader band noise, there are high and low pass filters. The low pass filter can be tuned to make the best of trying to reduce wind noise, for example, whilst the low pass filter can make a fair go at reducing hiss. But in both cases there is likely to be a change in the ambience of the retained sound, so the ability to preview the first few seconds whilst changing the parameters is very helpful. However, it remains as vital as ever to be very fussy about the quality of sound at the time of shooting, since at best such manipulations are a compromise.

For more complex problems, there is a 3-band parametric filter, which gives detailed control over frequency, bandwidth and gain for each of the three segments. A noise gate gives the facility to force quieter passages to absolute silence. There is also a 7-band graphics equaliser plus conventional bass and treble controls.

Mono sound can be accurately panned across the sound stage to give quasi stereo effects, eg of a passing car. The inverse effect can be achieved by filling both channels from either one of the left or right stereo originals. This could be very useful when two different microphones have been connected to the left and right channels during filming. And, for stereo tracks, left and right can be swapped.

There are other effects like reverb, multi-tap, equalise, flanger, boost and chorus for those with specialist requirements. And there's even a backwards filter if you need Russian-sounding dialogue or, perhaps, to have right-way audio from backwards video.

With 99 stereo tracks to play with, and the ability to mix CD-quality sound in stereo with all the flexibility for revision that marks the difference between the typewriter and the word processor, non-linear editing with Adobe Premiere offers far more than fancy visual effects for the video editor.

For those with PCs whose NLE software lacks sound-manipulation facilities, the cut-down version of Sound Forge (XP), is an attractive alternative and it can work directly on sound in AVI files. Sound Forge offers at least one useful facility absent from Premiere - stretching sound without altering pitch. So, if the sound track (especially a voice-over) is too long or too short for the visuals, you can change the length of the sound to fit (within about 10%, anyway). Now you know how the voiceover in financial adverts can cover the small print at such a fast lick.

It's a whole new, exciting world!

Page updated on 21 March 2008

Authors' views are not necessarily those of The Institute of Amateur Cinematographers

Free JavaScripts provided
by The JavaScript Source