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Monthly Archives: May 2007

Why Pro Tools needs Non-Destructive clip gain

Why Pro Tools needs non-destructive Clip Gain

– gain structure.

– better automation.

– region group exports.

1. Gain Structure.

Gain structure was very important in analogue recording studios to ensure the best possible sound out of the equipment – the perfect balance between noise and distortion.

In a digital recording system, gain structure is equally as important. However, mixing 16-bit sources (especially from mastered music and sound effects recordings) and 24-bit sources can cause lots of problems in a mix.

With reference to Bob Katz’s K-System, many of these sounds will initially be too loud, and will need to be attenuated.

The Pro Tools mixer deals with hot signals effectively by having enormous mixing headroom which can be realised by the effective use of master faders.

Insert Plug-in distortion

However, there is still a huge problem for plug-ins, because inserts are pre-fader.

The result of this is that any “hot” recording (peaks approaching 0dBFs) will most likely cause distortion in plug-in inserts.

Using a Plug-in as a temporary solution

One solution is to use an RTAS “Trim” plug-in to attenuate the audio before it goes through any other plug-ins. But, this applies globally to the track, and is really not appropriate when combining regions from different sources – which happens a lot with dialogue and sound effects editing.

Automating a Trim plug-in

You can, of course, automate the gain parameter in the Trim plug-in, and this automation will follow the region as it is edited, provided a similar automation enabled Trim plug-in is instantiated on every editing track.

One significant downside to this approach is that every track using this method of controlling gain structure sacrifices an insert point to do so.

Further Editing Problems

The automation method, however, does not adequately deal with regions that are crossfaded. Consider two regions that are adjacent and have a crossfade between them. If the editor wanted to increase the gain on one of those regions, an diagonal automation line must be drawn during the duration of the fade to preserve the clips loudness during the fade. This approach only works when using balanced fades. Any more complex fade is simply not possible to use.

In summary, gain adjustment of clips needs to be:

– pre fader (to assist with correct gain structure in a mix)

– pre insert (to prevent distortion, and prevent sacrificing inserts as a workaround)

– pre edit-fades (to allow customised fades to be used effectively)

2. Better Automation

The typical approach taken by sound editors to adjust the “loudness” of a region is to use volume automation.

This has some significant drawbacks:

– volume automation is not preserved

– sudden changes in volume automation are very difficult to work with on a control surface – faders are constantly jumping up and down very quickly.

– inadequate preservation of a region’s loudness during fades.

References:

“Mixing In The Box”, by Stan Coney

http://akmedia.digidesign.com/support/docs/Mixing_in_the_Box_26689.pdf

“Level Practises Part 1”, by Bob Katz

http://www.digido.com/bob-katz/level-practices-part-1.html

“Level Practises Part 2 includes the K system”, by Bob Katz

http://www.digido.com/bob-katz/level-practices-part-2-includes-the-k-system.html


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