In another great post from Sreejesh Nair's excellent blog we reproduce here an article Sreejesh wrote to try and answer some questions he received after making the Mixing in Atmos video and will also help to explain a little more about working in Dolby Atmos inside Pro Tools. Over to you Sreejesh...

One needs to understand the RMU before I can get to the local renderer. The RMU (short for Rendering and Mastering Unit) is what gives the whole Atmos Magic. It is a 19inch rack unit that is a system running Windows. It houses 2 MADI IO cards from where it takes the input and sends output. In addition to rendering the Pans in the speakers, it also takes care of the Studio Calibration and creating Room configuration for the Mix stage. It is this unit that is also used to create the Atmos Print Master. Room calibration is based on SMAART V7 that is pre installed on the RMU and helps with the Auto calibration. Once the calibration is done, another app called the Dolby Atmos Designer is used to set up the Room Configuration, where the engineer can input the number of speakers in the room walls, screen, ceiling, the distance between the speakers, the number of subs, the kind of speaker model, etc.

Once this is done, they would configure the arrays needed for the speakers. This would show which speakers are part of an array or the Bed. The reason is, if you remember, the screen wide speakers are not part of the beds.

So, as you can see, the RMU takes care of a lot of things in addition to just managing the pans.

The Local Renderer

The Local renderer is a stripped down version of the RMU. It is a software only version of the RMU that is used in edit suites that are not equipped with the hardware. It consists of a set of native AAX plugins for Pro Tools that are installed which let you prepare your tracks with objects, and pans with the Atmos plugin, and take it to a mix stage where these don’t need to be redone. You will need to have the Atmos Panner license for this to work, as this doesn’t provide you with that.

When you first run the Local Renderer installer, it will ask you for the room configuration of your edit suite, or where you plan to use this. The minimum config needed is a 9.1, so depending on the speakers and amps you would need a 16×16 HD I/O for this.

Once that is done, it installs the Local Renderer AAX plugin along with a Dolby Framework that takes care of the processing and also some configuration files for the kind of room you have chosen. When compared to the RMU, it can do only one thing. Provide for a Local adaptation of the atmos mix from a 9.1 config to 15.1. It cannot do room calibration, mastering, stitching, etc and so is not meant to be a replacement to the RMU.

This installer puts in 2 suites of plugins:

1. Local Renderer Input
2. Local Renderer Output

The Renderer Input plugin sends signals from Pro Tools to the local renderer. The Renderer output plugin takes the rendered signals from the Local Renderer and is used to input back to Pro tools so that you can send it to the required hardware outputs.

If the above was clear, then the set up of the local renderer is very easy to understand. You have to have the following auxes within your session:

1. 1 Bed Aux
2. Stereo Overhead Aux
3. Object Mono Aux equal to the number of objects being used in the project. (Note that it has to be mono for the local renderer as there is no stereo version of the Renderer Input Plugin, nor a multi-mono version.)
4. Split Mono Auxes for return. (If the config is 9.1, then it will be 10 auxes, and so on upto a max of 16 auxes for 15.1)

If you consider Point no 3 above, then you don’t need to make 128 objects. For example, if you are cutting and designing effects, and after a discussion with the recording engineer, decide that you would be using 30 objects in total for this, then you need to make just 30 objects. I advise to have a few extras in it as buffers in case at the stage we need some for reverbs or additional designs or so.

This is one part of the prep. The second part is sending signals to these auxes. For that, there are 2 ways:

1. Have all the beds sent to an aux and send that aux to the Local Renderer Aux
2. Have sends from your channels to the Local Renderer Aux.

Usually Method 1 is preferred as the number of sends is reduced and it also gives more control on the mix. For the Objects, usually one technique is to have multiple tracks but the atmos panner on just one of all those tracks follow the same pan. As an example, if a car pass is made of the tyre, engine low, engine high, horn, and a screech, then these may be on different tracks, but follow the same pan. In this case, the panner is put on just one track. So, these can be sent to a bus that is routed to an Aux for the object. Now, these combiner auxes (I just made that up!) have a physical output that is mapped to the output in the mix room. So the Beds will have output from 1 to 8, Overheads will be 9 and 10, and objects will start from 11 onwards. These MADI outputs won’t be present in the edit stage.

But that’s ok. Assigning sends on those tracks to the local renderer aux covers this. So, when you take the mix from the edit to the mix, the Local Renderer tracks will be inactivated. Getting it back and reactivating these will let you move the session back and forth between studios without changing the IO. In the above image, all the purple tracks are the returns from the Local Renderer that are routed to the 9.1 outputs in the edit studio. The Green tracks are the Inputs that are being sent to the Local Renderer. The following table will help you with the ID No of the Renderer Output and the speaker it is supposed to be mapped to.

Checking the Local Renderer

When you have the session set up, launching the Dolby Atmos Monitor app, will let you select the Renderer present in the network. Since you don’t have an RMU, you can select the local one and it will turn green. At this stage, depending on whether you set up your install of the local renderer as a 9.1, or above, the number of speakers will change in the Atmos Monitor as it will read the corresponding Configuration file.

All you need to do now is to save the session as a template and you are good to go! Let me know if there are questions in the comments below.