Structuring an Audio Post-Production Project

To organize their projects, most video and motion picture sound editors combine the signals of related tracks and busses into submixes (also known as stem mixes). Then they combine these submixes to build a final mix. Soundtrack Pro is designed with this workflow in mind.

What Is a Submix and How Do You Use It?

In Soundtrack Pro, you use a submix to combine (or “sum”) the audio from different tracks and busses, and route the audio to physical outputs. The name of this feature implies its purpose—to mix the audio signals of a subset of the tracks and busses in your project. If you are using external audio hardware that supports multiple physical outputs, you can have multiple submixes in your project and then choose the physical output to which each submix routes its audio. By default, all tracks are routed to Submix 1, and Submix 1 is routed to the Stereo 1, 2 outputs. You can easily add more submixes, reroute audio, and change the hardware output setting using the Output pop-up menu in each submix.

Basic Signal Routing in Soundtrack Pro

At a minimum, any audio that you edit in the Soundtrack Pro Timeline passes through the following “mixer objects” on its way out to the physical audio outputs: a track, a submix, and the Master bus.

Figure. Diagram showing a typical signal path in Soundtrack Pro.

Audio post-production projects typically include many tracks and submixes. The following diagram shows the signal flow of multiple tracks to just one submix. While this is an unlikely scenario, it illustrates the fact that you can route as many tracks to a submix as you like. See Example: Mixing a Project with Submixes for a typical example.

Figure. Diagram showing the signal flow of a number of tracks to a submix.

Setting the Submixes for Tracks and Busses

To be included in a project, the audio signal of each track and each bus must be routed to a submix. By default, in new multitrack projects, there is only one submix (Submix 1) and all tracks are routed to Submix 1. You can add as many submixes as you like and route as many signals from tracks and busses to those submixes as you want.

To create a more elaborate project (as described in Example: Mixing a Project with Submixes), you create additional submixes.

To add a submix
Do one of the following:
  • Choose Multitrack > Add Submix.

  • Control-click a submix, then choose either Insert Submix Before or Insert Submix After from the shortcut menu.

Once you have created multiple submixes, you can route any combination of tracks or busses to any submix.

To set the submix for a track or bus
  • Choose the submix from the Submix pop-up menu in the track header or at the bottom of the Mixer channel strip for the track or bus.

    Figure. Submix pop-up menu.

    If you choose None from the pop-up menu, you are effectively removing that track or bus from the mix and from the final output.

Setting Hardware Outputs

Use the Output pop-up menu in each submix to choose an output channel or set of output channels. Your choice defines the output of that submix as either mono, stereo, or surround.

To select the hardware output jacks for a submix
  • Click None, Surround, Stereo, or Mono from the Output pop-up menu in the track header of each submix, then choose a channel or set of channels from the submenu.

    Figure. Output pop-up menu.

    The available choices within each of these output categories depend on the number of available physical outputs and number of submixes in your project.

    If you choose None from the Output pop-up menu, you are effectively removing that submix from the mix and from the final output.

    Note: You can create submixes independently of the audio hardware connected to your computer and can route audio to an output that does not correspond to a physical output. In most situations, each submix in a project should correspond to a physical output on the audio interface or other hardware connected to your computer. Submixes that do not correspond to a physical output will not be heard. You may set as many submixes in a project to the same physical output device or output channel as you like.

For more information about system output settings, see Setting the Audio Input and Output. For more information about connecting an audio interface, see Setting the Audio Input and Output.

For more information about working with tracks, busses, and submixes in the Timeline, see Tracks, Busses, Submixes, and the Master Bus and Working with Tracks, Busses, and Submixes in the Timeline.

Example: Mixing a Project with Submixes

A classic audio post-production practice for film and video is creating separate submixes for the dialogue, the music, and the sound effects. This provides an appropriate degree of flexibility, both in the mixing phase and in distributing the final product.

Creating Submixes

In this example project, all tracks containing dialogue are routed to a submix called “Dialogue.” The tracks containing sound effects are routed to a submix called “FX.” The tracks containing music are routed to a submix called “Music.”

Figure. Track headers example with tracks arranged by function showing dialogue tracks, effects tracks, and a music track.

The following diagram shows how audio signals from tracks in each category are routed into their respective submixes.

Figure. Diagram showing track categories sent to submixes.

Once the audio signals are organized in this way, you can apply (and automate) volume settings and effects on any of the submixes, rather than on the individual tracks or busses. You might, for example, add a compressor or EQ effect to a Dialogue submix to enhance all of the dialogue signals at once. Obviously, this saves a lot of time and effort (when compared with applying all of these settings to each dialogue track individually). Using submixes to segment your project provides you with greater control over all aspects of your final mix.

Creating a Stereo Mix

The next routing decision is the choice of hardware outputs. The following example diagram shows the routing for a traditional final product: a stereo mix. To do this, you would simply choose the Stereo 1,2 output for each of the three submixes. (This also happens to be the default output for every submix in Soundtrack Pro.)

Figure. Diagram showing tracks and submixes sent to final stereo output.

In this case, the left and right channels for each submix are routed to the left and right (1 and 2) channels of the hardware output device. All three submixes are combined into one stereo (left and right) signal. This is a “stereo mixdown,” suitable for any stereo-capable playback device. At this stage, the Master bus presents a (final) opportunity to make volume adjustments and apply effects. For information about the Master bus, see Using the Master Bus.

Creating a Separate Music and Effects Mix

Using submixes in your workflow becomes very powerful when you consider the many different ways you might be delivering the final program. One common practice is creating a separate music and effects (M & E) submix for foreign distribution. This gives distributors the option to create versions of the program with the dialogue dubbed in foreign languages but to still include the program’s original music and effects in the dubbed versions.

Figure. Diagram showing a four channel mix with dialogue on the first two output channels, and music and effects on the next two channels.

As in the stereo mixdown example, the Dialogue submix is routed to the Stereo 1,2 output. But the Music and Effects submixes are routed to the Stereo 3,4 output channels, isolating the dialogue signal from the music and effects signals. Technically, only one output channel is required for the dialogue, because the Dialogue submix is made up of mono signals. But in practice, it is usually routed as two identical mono signals to channels 1 and 2. Most likely, producers making the foreign language version will use the original dialogue as a guide track and then replace it with their edited foreign language track in the final mix.

This M & E case is just one simple example of how you can structure a project for an efficient workflow. Each mix project comes with its own particular quirks. The good news is that Soundtrack Pro has a lot of flexibility. For example, the sends and busses features in Soundtrack Pro offer additional options for structuring a project. For more information, see Working with Sends and Busses in the Mixer.

Signal Routing for a Separate Music and Effects Mix in Surround

When you shift from a stereo project to surround, you need to keep in mind some minor signal routing consequences. This section discusses what changes you would make to the submix and output settings. (For information about creating a surround version of a stereo project, see Converting a Stereo Mix to 5.1 Surround.) First, assuming that the music and effects are mixed over six surround channels, those submixes must be routed to the Surround 1-6 output. The Dialogue submix could either remain routed to the Stereo 1,2 output jacks to be added to the Surround 1-6 mix or routed to the center channel at the submix, or could be panned to the center channel in a surround signal, as shown below.

Figure. Diagram showing signal routing for a 6-channel surround mix.

To create the surround version of the separate music and effects mix (as described earlier), you route the Dialogue submix to any output channels other than 1-6. This example uses channels 7 and 8, the last two available output channels, thus isolating the dialogue from the music and effects.

Figure. Diagram showing signal routing for a separate music and effects mix in 6-channel surround.

Using Sends and Busses

You can use sends to split an audio signal into two or more separate signals. A send taps a track’s audio signal and routes it down a separate but parallel path. In Soundtrack Pro, these separate paths are known as busses. (Some might call these auxiliary busses.) This process is analogous to diverting a portion of a river to an alternate (but parallel) stream. Busses are like alternate streams of audio. They can be processed or combined independently of the “main river.” They can rejoin the main signal further “downstream,” at the final mix, or they can be routed to altogether separate outputs.

Figure. Diagram showing how a signal is sent through a send to a bus and then back to a submix bus.

By preparing these alternate versions and combinations of track audio signals, you give yourself more options at the final mix stage, when all of your project’s media elements and adjustments are in place.

For an example of adding effects with sends and busses, see Example: Adding Effects with Sends and Busses.

For an example of combining track signals with busses, see Example: Combining Track Signals with Sends and Busses.

Example: Adding Effects with Sends and Busses

The following example shows how you could add a reverb effect to a music track using a bus. The main reason to apply effects this way (rather than directly on the track) is so you can control the amount and characteristics of the effect (in this case, reverb) on multiple tracks using one set of controls.

For more information on using sends and busses, see Using Sends and Busses.

To add a reverb effect to a music track using a bus
  1. Create a new bus. (In this example, the new bus is named “MusicReverb.”)

  2. Add a send to the music track.

    For specific information about how to add sends to tracks and route them to busses, see Adding Sends to Tracks.

  3. Route the new send to the MusicReverb bus.

  4. Apply a reverb effect to the MusicReverb bus.

Figure. Diagram showing a reverb effect applied to a music track using a bus.

As the diagram shows, the new MusicReverb bus represents an alternate version of the Music track audio signal. Once created, this bus appears as a row in the Timeline and a channel strip in the Mixer. It becomes a resource to draw from during the final mix. Rather than having to tweak the effects settings of individual tracks in the mix, you can simply adjust the volume fader on the MusicReverb bus to increase or decrease the amount of reverb on that music track.

By default, new sends are post-fader sends. This means the signal is tapped after the track’s output fader. In this example, adjusting the Volume slider on the Music track would have a direct effect on the music level in the MusicReverb bus.

Figure. Diagram showing the signal path using a post-fader send.

In contrast, a pre-fader send taps the track signal before a track’s output fader. You can change a send to a pre-fader send.

To make a send a pre-fader send
  • Click the disclosure triangle for the send in the Effects tab, then choose Pre-Fader from the Send Type pop-up menu.

Figure. Diagram showing the signal path using a pre-fader send.

In the pre-fader case, adjusting the Volume slider on the Music track would have no effect on the music level in the MusicReverb bus.

Example: Combining Track Signals with Sends and Busses

You can also send the signals from multiple tracks to a single bus, creating “intermediate submixes.” For example, you could route every dialogue track for a particular actor to a bus with the actor’s name. You could adjust the volume of all the actor’s dialogue using the bus volume fader and add an EQ effect that brings out the actor’s voice in the mix. You could then send (route) the bus to a particular submix.

For more information on using sends and busses, see Using Sends and Busses.

Figure. Diagram showing an example of track signals combined with sends and busses.

In the above diagram, tracks 1 and 4 contain dialogue from the actor, Jacob. Each of these tracks has a send applied to it that taps the signal and routes it to a bus (named “Jacob”). This bus is effectively an intermediate submix. Now, any effects and fader adjustments applied to this bus will be available during the final mix as a single channel strip (named “Jacob”).

For more information about using sends and busses in the Mixer, see Working with Sends and Busses in the Mixer.