Surround Mixing Strategies

This section includes guidelines and tips for mixing surround projects.

Mixing Surround Files

The basic steps in mixing are almost the same for stereo and surround projects:

  • Balancing relative volume levels between tracks

  • Panning tracks to create a balanced stereo spread

  • Adding EQ, compression, and other final processing effects

  • Setting the project’s final volume and eliminating clipping

  • Creating a sense of perspective by placing sounds in space

While the creating a sense of perspective step is also a part of stereo mixing, it is what really sets surround apart from stereo. When mixing, you can enhance the video action by dynamically moving the sounds within the surround field. To give your listeners a “surrounding” audio experience, your sound must be created with that goal in mind. For example, if you want the sound of an explosion coming from behind the listener, you need to put the sound in the rear channels during mixing. Surround mixing adds not only two rear channels, but also includes the subwoofer or LFE channel, which would probably play a part in any onscreen explosion. You’ll have to spend some time planning what elements go where and how much boom you want in your soundtrack.

The following are some common approaches to multichannel sound:

  • Use the surround channels for effects only. Create a stereo mix, then add “sweetening” sound effects in the surround channels. Sound effects and Foley recordings can be placed in stereo space or specifically located where they occur onscreen or offscreen.

  • Create special sounds for the rear and low-frequency channels (the rumble of an earthquake, the pounding of drums, an airplane buzzing overhead, and so on) and add them to a standard stereo mix. (To create sound for the LFE channel, you can extract low frequencies from the rest of your sound using band-pass filters.)

  • Position instruments, effects, and voices anywhere in the sound field.

Converting a Stereo Mix to 5.1 Surround

Many post-production projects require both a stereo mix and a surround mix. This section reviews some best practices for converting projects from stereo to surround. You can reverse the steps below to convert a project from surround to stereo.

Important: When you switch between stereo and surround panners, panning automation (envelope) settings are not automatically copied over to the new panning mode. Volume information is automatically copied over between stereo and surround panners. The recommended workflow for making a surround version of a stereo mix is to maintain at least two separate versions of the project: a stereo version and a surround version.

To create a separate copy of your stereo mix for surround mixing
  1. Choose File > Save As in your stereo project to save a separate copy.

    In the dialog that appears, indicate in the filename that this is the surround version; for example, “My Great Mix_surround.”

    Figure. Save As dialog.
  2. Use this copy of the project to make all the necessary surround panning adjustments.

    In particular, you Control-click the stereo panner in the track header (or Mixer channel strip) of each appropriate track or bus and choose Use Surround Panner from the shortcut menu.

    Figure. Track headers with all panners set to surround mode.

    Note: To save time, you can select or group all tracks or busses in the Tracks tab. When you change the panning settings of one of the tracks or busses, the panning settings on all the grouped items change as well.

  3. If you previously applied any left-right panning to any tracks or busses in the stereo version of the project, do the following:

    1. Select the tracks or busses.

    2. Control-click the panner in the track header, then choose Replace Surround L/R with Stereo L/R from the shortcut menu.

      Figure. Track header showing shortcut menu.

    Any panning automation (envelope) information is copied from the stereo left-right pan to the surround left-right pan (specifically, to the Surround Pan X parameter) in the selected tracks and busses. These settings can be used to provide a starting point for your surround mix.

    Note: If you are converting a surround project to a stereo project, you can choose Replace Stereo L/R with Surround L/R from the shortcut menu to do the reverse of step 3.

Placing Dialogue and Voiceover in a Surround Mix

In a surround mix, dialogue usually goes directly into the center channel. This is particularly true for voiceover narration, which is best left out of the left and right channels. (This is called stereo plus center.) Soundtrack Pro allows you to place sounds exclusively in a specific channel or just outside that channel, which would allow some of the sound to leak into the other speakers. As you get more comfortable with surround mixing, you may want to experiment with alternative placements to further reinforce the voices that you place within your mix.

To place dialogue and narration in the center channel
  1. If you haven’t already done so, Control-click the stereo pan slider in the track header of the dialogue track (or bus), then choose Use Surround Panner from the shortcut menu.

  2. Double-click the surround panner.

    The Surround Panner HUD appears.

  3. Drag the puck to the center speaker icon.

    Note: You can hold down the Option key as you drag the puck to constrain its movement to a straight line.

Depending on the current Collapse slider setting, the arc at the center speaker icon either turns white to indicate exclusive output or is elongated to indicate the increased gain.

Figure. Examples of center speaker icon in exclusive mode and in increased gain mode.

Placing Stereo Music in a Surround Mix

The simplest option for stereo music in a surround project is to just leave it in stereo. If you just use the stereo panner for a music track, the left and right signals remain in their respective channels. However, some surround mixes include a hint of music in the rear channels as well. With the Surround Panner HUD, you can place the right music channel somewhere between the right front and right rear position, with more emphasis on the front speaker. Do the same with the left side and listen to the mix. Make adjustments as needed.

Using the Center Channel

In a multichannel system, there are three ways to achieve a centrally placed sound image:

Create a “phantom center” (mix sound to the left and right equally, as with stereo)

This is a common strategy, but it assumes the listener is seated exactly between the speakers. The timbre of sound is not the same as from a direct speaker because of cross-cancelation effects.

Use the center channel alone

This creates a stable center image for listeners in any location. (To prevent the audio from sounding too focused or narrow, its reverb can be spread to the left and right channels.)

Use all three front channels equally or in various proportions

This method allows for greater control of the range of spatial depth and width. The phantom center can be reinforced by additional signals in the center channel, which can be enhanced by signal spread into the left/right pair. The disadvantage is that sound from all three speakers may not blend well or may not arrive at the listener at the same time, causing side effects such as comb filtering, shifts in tone color, or smearing. To counteract these side effects, you can first process the additional signals to change their spatial character, timbre, or prominence relative to the main center signal.

Using Surround Channels

Subtle surround effects can greatly enhance the listener’s sense of depth compared to conventional stereo. Popular music often benefits from creative use of surround. But don’t overdo it. The film industry guideline for visual effects applies equally well to surround effects—don’t let effects distract the listeners from the story.

Using Surround Effect Plug-ins

Soundtrack Pro includes a collection of professional surround-specific effect plug-ins for shaping your surround mix, including Surround Compressor, Delay Designer, Space Designer, and Multichannel Gain.

For a complete list of these true surround effects and a full description of each, see the Soundtrack Pro Effects Reference document, available in the Help menu. For information about using processing and realtime effect plug-ins, see Working with Audio Effects.

Limitations of the LFE Channel

Use the LFE (Low Frequency Effects) channel to enhance the low frequencies of a film or video so you get the extra boom out of an explosion, thump in a car crash, and so on in dramatic scenes involving plenty of low frequencies. The low frequency effects (LFE) channel is a separate signal with a limited frequency range (about 25 Hz to 120 Hz). It is created by the mixing engineer and delivered alongside the main channels in the mix.

In soundtracks comprised entirely of music, the LFE channel is not necessary. (An exception to this rule might be the famous cannon shots in Tchaikovsky’s “1812 Overture.”) The LFE signal is also discarded in the downmix process, so that intense bass signals do not stress small stereo systems. Be sure not to include vital information (such as dialogue) in the LFE channel that would be missed in mono or stereo playback.

Because LFE is separate from other channels, its ability to blend with higher frequencies can be affected by filters used to generate the LFE signal. To ensure a cohesive audio signal, keep the entire signal together in the main channel or channels.

Note: If you are creating Dolby Digital Professional (AC-3) output, avoid creating an LFE channel for material originally produced without one. Dolby Digital Professional’s five main channels are all full-range, and the LFE channel does not increase the frequency response. Dolby Digital Professional decoders offer bass management, directing low frequencies to a subwoofer or other suitable speakers. An LFE track may interfere with bass management. For more information about Dolby Digital Professional, see the Dolby Laboratories Inc. website at http://www.dolby.com.

Accommodating Stereo Playback

Even with the popularity of 5.1 systems, you should always address stereo reproduction. There are three basic ways to do this:

  • Prepare a new stereo mix from the original multitrack elements (using conventional stereo-mixing sessions).

  • Prepare a studio-adjusted downmix from the multichannel mix. This method takes advantage of the work that has gone into mixing the 5.1 version. It retains flexibility in the exact proportions of each channel represented in the final stereo mix.

  • Let the decoder derive a stereo downmix, based on preset formulas in the decoder. Downmix options and dynamic range control effects can be previewed and adjusted in the production studio, and a range of adjustments is possible.

Tip: Always check the mix on an inexpensive surround system to evaluate how well it sounds on modest playback systems.