ProTools: The Mix

Using Buses and Aux Channels:

You can automate several channels together by using groups. Click on a track name, then shift-click on any other track names that you'd like to treat the same, then hit "command G" and name the group. Then, any automation will control all tracks in the group together. But there are even more flexible and powerful ways to do the same thing. Let's say you have several tracks that all need to move up or down in unison, such as layered tracks of ambience, or several overlapping voices, but you'd like to retain the ability to easily tweak the individual elements as well. Bouncing would eliminate your ability to change the balance among the tracks. You could simply highlight the tracks and make a group, which would let you write automation data to all the grouped tracks equally. But it can get quite dizzying if you want to adjust an individual element's volume, forcing you to cancel the group, perhaps re-select a subgroup, make the change, re-activate the group, and if you don't like the change, you can't easily get back to where you started.

But if the outputs of the tracks in question are sent to a "bus" instead of the main stereo mix, they can be returned to the main mix through an aux channel. That aux channel can then be automated or have effects applied to it, adjusting all sounds sent to that bus equally. This is also an excellent, resource-saving method for processing a group of tracks that need similar treatment. If several channels all need the same kind of compression, or EQ, don't insert a plug-in on every channel, bus them together and insert one effect on the aux channel where they return.

A bus can be mono or stereo, and which one is best will depend on what sounds you are busing. If all the tracks are mono and can share the same pan position, choose a mono bus. If you would like the tracks to have individual placements across the stereo spectrum, or if you are busing stereo tracks, choose a stereo bus.

Forced Bussing:

Using buses creates an intermediate grouping of tracks before the final output, which allows you to adjust several tracks in one step. Buses are often used in music mixing to simplify control of related inputs. For instance, if there are 8 or 10 mics on a drum kit, these channels can be routed to a bus before the main outputs. Audio from those channels can then be controlled by a single bus fader. That way each channel can be tweaked separately, and the bus master can be adjusted to raise or lower the overall level of the drums.

In the example below, tracks 3, 4 and 5 are routed to buses 1-2. Bus 1 and 2 are selected as the inputs for an Aux channel. If you have found a balance of the three ambiences that you like, but want all of the ambience to duck under the narration or acts, you can pull-down the level of the Aux channel which will adjust all of the ambience tracks at once. And if all of the ambience had rumble or hiss that needed EQ, you could apply plug-ins to the aux channel rather than to each individual track, saving processing power by reducing the number of plug-ins needed.

On the track's channel strip in the edit window, click on the "output" box and select a bus, or pair of buses, rather than the main stereo outputs. Repeat this for all channels you want to adjust together. Then create a new aux track, mono or stereo, depending on which type of you need. Then, on that new aux track, click on the "input" box of its channel strip, and select the name of the bus(es) where you just routed the individual tracks. All channels that you designate to be output through the bus, rather than the main stereo output, will be routed through this aux channel first, and then to the main output.

That aux channel can now be treated like any audio track, with plug-ins, volume changes, panning changes, etc. Adjustments made to the individual audio tracks will still have an effect, but you can also affect all channels assigned to that bus together, applying the same compressor or EQ to several different tracks of voices, or tweaking the volumes of layers of tracks.

Yes, Master...

Try to always use a master fader, it not only creates a quick way to see if your final mix levels are correct, but also creates one more stage at which effects or automation can be applied. An EQ or compressor inserted on the master fader can bring a mix together in a way that individual track adjustments cannot.

If a sonic element has unique problems, apply plug-ins to that track alone. A compressor on the master fader will unpleasantly squish background sounds if one track gets too loud. Rumbles, hisses or peaks are better dealt with on specific channels, or if shared by several tracks, on a bus. A gentle gain-controlling compression and peak-limiting, and overall EQ smoothing are best applied to the master fader.

With or without effects, remember that all the tracks are interacting, sometimes the way to make an element more prominent in the mix is to reduce the level of the other tracks, rather than turning it up. Or as is routinely done in music mixes, make room for the primary sound by EQing the background to clear out the frequency ranges that compete.

And in the end, use your ears to decide what's right. Digital editing programs have the tremendous advantage of providing visual feedback that can help make decisions, but in the end, it doesn't matter how lovely your automation curves are drawn, it matters how your mix sounds.

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