Downmix and trim controls in Logic Pro for Mac

When mixing in Dolby Atmos, you can use bed tracks to pan signals in a channel-based format using the channel strip’s Surround Panner. With object tracks, you can position signals in your mix freely in the three-dimensional listening environment using the channel strip’s 3D Object Panner. A Dolby Atmos mix is always rendered to a dedicated speaker layout (such as 7.1.4, 5.1, or stereo) or a two-channel binaural mix for monitoring and creating a surround bounce. In Logic Pro for Mac, you make that selection in the Monitoring Format pop-up menu of the Dolby Atmos plug-in. It determines what format your Dolby Atmos mix is rendered to when playing back your project and when bouncing it to an audio file. For information about the various monitoring formats, see Dolby Atmos monitoring formats in Logic Pro for Mac.

Depending on the selected monitoring format, the renderer has to determine how to fold down the immersive mix to a limited number of speakers (for example, 5.1.2), to a speaker layout that doesn’t have height channels (for example, 7.1 or 5.1), or to a 2.0 speaker layout that doesn’t have surround channels at all (stereo). The downmix and trim controls in the Dolby Atmos plug-in let you customize the renderer algorithms for certain monitoring formats (2.0, 5.1, 5.1.2, 5.1.4 and 7.1). When you create the Dolby Atmos master file by exporting to an ADM BWF file, those settings will be stored with that file and will be used by any Dolby Atmos playback device. The downmix and trim settings have no effect when you’re listening or bouncing to one of the five binaural formats. To learn more about the binaural formats, see Dolby Atmos monitoring formats.

Note: Because the Dolby Atmos plug-in renders the immersive mix to the selected monitoring format in real time, you can hear the changes when you adjust the downmix and trim controls during playback. Those settings are also applied when you bounce your mix to a channel-based format, such as 5.1 or 2.0.

Downmix Controls

When you select the 7.1.4 monitoring format, the Dolby Atmos plug-in renders the three-dimensional Dolby Atmos mix to the 7.1.4 speaker layout based on a fixed algorithm. For other speaker layouts, you can choose from various algorithms, which you access in the following two pop-up menus:

5.1 and 5.1.x pop-up menu: Choose an algorithm for downmixing your Dolby Atmos mix to a 5.1 speaker layout, with or without height channels:
- Lo/Ro - default: This algorithm (Left only / Right only) renders the Dolby Atmos mix to 7.1 and then downmixes it to 5.1 using the following coefficients:
  Ls = 0 dB × Lss + 0 dB × Lrs
  Rs = 0 dB × Rss + 0 dB × Rrs
- Dolby Pro Logic IIx: The Dolby Atmos mix is rendered to 7.1 and then downmixed to 5.1 using the following coefficients:
  Ls = Lss + (–1.2 dB × Lrs) + (–6.2 dB × Rrs)
  Rs = Rss + (–6.2 dB × Lrs) + (–1.2 dB × Rrs)
- Direct render with room balance: The Dolby Atmos mix is rendered directly to 5.1 (without downmixing to 7.1), using algorithms that process signals panned between the midpoint and back of the room.
- Direct render: The Dolby Atmos mix is rendered directly to 5.1 (without downmixing to 7.1) for optimal sound field recreation at the central listening position using phantom imaging between the front speakers and surround speakers.
5.1 to 2.0 pop-up menu: Choose an algorithm for downmixing your Dolby Atmos mix to a 2.0 (stereo) speaker layout. It is derived from the downmix option selected in the “5.1 and 5.1.x” pop-up menu.
- Lo/Ro - default: The center and surround channels are added to the left and right channels of the stereo output at a reduced level and the LFE channel is ignored.
  Lo = L + (–3 dB × C) + (–3 dB × Ls)
  Ro = R + (–3 dB × C) + (–3 dB × Rs)
- Lt/Rt (Dolby Pro Logic II): This format (Left total / Right total) converts a 5.1 mix to stereo using the following encoding matrix:
  Lt = L + (–3 dB × C) – (–1.2 dB × Ls) – (–6.2 dB × Rs)
  Rt = R + (–3 dB × C) + (–6.2 dB × Ls) + (–1.2 dB × Rs)
- Lt/Rt (Dolby Pro Logic II) w/ Phase 90: This option is recommended for Lt/Rt downmixes because of the improved performances, such as reducing undesirable signal cancellation, improving imaging, and enabling proper matrix decoding.

Trim Controls

The four sliders in the Downmix & Trim pane of the Dolby Atmos plug-in can be adjusted separately for the four channel layouts, represented by the four Channel Layout buttons: 5.1 & 2.0, 5.1.2, 5.1.4, and 7.1. They are applied before the downmix stage.

Channel Layout buttons: Click one of the four buttons to select the corresponding trim settings for that channel layout.
Tip: Select the corresponding speaker layout in the Monitoring Format pop-up menu to listen to the results of your adjustments.
Mode pop-up menu: For each of the four channel layouts, choose from two options:
- Automatic: Default values are applied to all trim controls.
  Note: The four sliders and value fields are dimmed, displaying the default values.
- Manual: The four sliders are active, and you can adjust them individually for each of the four channel layouts.

Trims

The two sliders let you reduce the levels of the surround and height content in your Dolby Atmos mix when downmixed to a smaller speaker layout.

Surround slider: Adjust the slider to reduce the level of the surround channels.
Height slider: Adjust the slider to reduce the level of the height channels.

Tip: Select the downmix speaker layout in the Monitoring Format pop-up menu (for example, 7.1 or 2.0) to monitor the result of the trim settings.

Front/Back Balance

The two sliders let you change the levels between the front and back of the height speakers (Overhead) and the front and back of the ear-level speakers (Listener plane).

Overhead slider: Adjust the front/back level balance of the height content in your Dolby Atmos mix during the downmix.
Listener plane slider: Adjust the front/back level balance of the ear-level content in your Dolby Atmos mix during the downmix.

The center position (0%) leaves the mix unchanged. Moving a slider to the right shifts the balance to the front speakers, and moving a slider to the left shifts the balance to the back speakers.

Choose a downmix algorithm for the Dolby Atmos mix

In the Dolby Atmos plug-in, click the List button in the upper-right corner of the plug-in window, then click the Downmix & Trim button.
Click the “5.1 to 2.0” pop-up menu or the “5.1 and 5.1.x” pop-up menu, then choose a downmix option.

Adjust the downmix and trim controls of a Dolby Atmos mix

In the Dolby Atmos plug-in, click the List button , then click the Downmix & Trim button.
Choose an option from the “5.1 and 5.1.x” or “5.1 to 2.0” pop-up menu.
Click one of the four channel layout buttons to select the speaker layout for which you want to make the adjustments.
Click the Mode pop-up menu, then choose Manual.
The sliders and value fields become active.
Adjust the values by dragging the sliders horizontally or dragging the value fields vertically.

Tip: When mixing a recording of classical music or a Jazz ensemble, the surround and height speakers usually contain room information, not individual instruments, as is common with immersive mixes for pop music. When such a Dolby Atmos mix is rendered to a speaker layout that doesn’t have height speakers or even surround speakers, all those signals would be folded into the front speakers, resulting in an unbalanced mix with too much room information. In such a case, the trim controls allow you to reduce those height and surround levels in the downmix.

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