Multi-Channel Audio

Overview 

Rack Overview

1. Rosendahl Nanosync
2. SSL to Genelec 1-24 
3. Ghielmetti 
4. RME UFX+
5. RME OctaMic II
6. Analog board for Qualisys
7. Preamp for ceiling mics (talkback system)
8. Power for preamps

Quick Start Guide

Full lab start routine (turn on):

Bigknob, Videomixer (Sony MCX-500), MoCap + Audio PCs, HDMI-matrix, TVs (lab), audio interface (Rosendahl masterclock clock, SSL, RME UFX+, RME Octamic, Preamp Power), Circuits F11(Speakers)+F13(Oqus)+F19(Canon)

Specifically to the multichannel audio system, start routine

1. Audio PC
2. Audio interface (Rosendahl masterclock clock, SSL, RME UFX+, RME Octamic)
3. Power Circuit F11(Speakers)

Audio Output 

Speaker Setup

RITMO lab has in total 24 separate Genelec 8020 speakers. These are active speakers with its own XLR (female) input. 16 of these speakers are mounted in the rig and 8 are free standing on the floor.

When working with spatial audio applications, these free standing speakers should be placed in the red-taped marks in the floor to match the right placement regarding the complete setup as indicated below, and facing to the center, which is also marked as illustrated.

On the below figure you will see that the 16 rig mounted speakers + 8 floor standing speakers are divided into four zones (A to D), with its own color. The 6 speakers in each zone is connected to the same XLR + power patch. Each speaker has a unique number (DAC 1-24) associated with the patching setup. 

Cables going into the control room patch, out of the lab-patch and into the speakers are now all labeled like this: 

"DAC X  -  Zone+Number" (e.g. "DAC 15  -  D37")

From here, 24 of the channels are fed into Ghielmetti pach and further in to the SSL for control with the audio computer.

We have normalized the Ghielmetti patch. This means that channel 1-24 in the software matrix are routed to speakers clockwise in three different circles; floor, outer roof and inner roof. Each circle contains 8 speakers.  

The speakers placement is described with Cartesian and spherical coordinates as the previous figure illustrates. Some of these values has been calculated from one domain to another as indicated in the spreadsheet "cartesian-spherical-calculations.xlsx" found in the audio PC at "Desktop/TEMPLATES" or here.

Playing Sound

The immersive rig is run from the audio computer using Reaper as the suggested DAW. Sound is sent from the Computer -> RME UFX+ -> SSL -> Ghielmetti -> Patch -> Lab Zone Patch -> Speaker.

Default SSL Configuration:

Regardless of the environment you use, make sure to use outputs Madi 1-24. The configuration for the speaker routing is in TotalMix, which can be accessed through the bottom right section of the audio PC.

In TotalMix the outputs and inputs can be mapped accordingly. The default configuration allows to playback sound over the structure described in this documentation (24 speakers through Madi 1-24)- In case it has been changed or you need to restart this default settings, files for TotalMix can be loaded from the folder "Desktop/TEMPLATES/TOTALMIX TEMPLATES" in the audio PC or from here if they are not found.

Front Ports in RME interface: Monitor Audio and Additional Analog Inputs

The RME UFX+ interface presents a front interface in which additional analog inputs can be used as well as phones to direct monitoring if needed. This interface is shown below.

You can note in red two 1/4 jack ports to connect additional outputs (usually headphones for monitoring). 9/10 correspond to 'Phones 1' in TotalMix and 11/12 to 'Phones 2'. The 4 Mic/Line inputs in the green group corresponds to inputs 'Mic 9' to 'Mic 12' in TotalMix. Below you will find the mapping. In the case of the phones, everything from 'SOFTWARE PLAYBACK' (middle row) is routed as well as the 'ADAT' inputs from 'HARDWARE INPUTS' (in the upper row), so every input and output in the software routing can be heard from a device connected to the phones output, and just the direct ADAT inputs. This can be changed according to routing needs. In the case of inputs, they can be used in a DAW or routed to any output, depending on the application.

Playback Templates

The default playback configurations through Reaper can be found in the session file 'playbackDefaultSession.rpp' in the audio PC at "Desktop/TEMPLATES/REAPER TEMPLATES" or can be downloaded here. The session is depicted below.

There are 4 groups for different playback needs, all of them are muted by default. It is recommendable to copy this file to a new one for performing modifications. You can add as many tracks (mono or stereo) as you need under each group. These groups are described below:

• Stereo Track - Speakers 1 and 8: It sends the stereo signal to speakers 1 and 8 standing on the floor. You can move those speakers as you please.
• Floor ring - Speakers 1-4(Right) 5-8(Left): It sends the right signal to speakers 1 to 4 and the left signal to speakers 5 to 8. This speakers ring is the one standing on the floor, so there is flexibility to move them accordingly.
• Outer ring - Speakers 9-12(Right) 13-16(Left): It sends the right signal to speakers 9 to 12 and the left signal to speakers 13 to 16.
• Inner ring - Speakers 17-20(Right) 21-24(Left): It sends the right signal to speakers 17 to 20 and the left signal to speakers 21 to 24.

For the last three groups, a spatial audio solution is used for distributing the left and right signal, thus the directionality can be changed if necessary. Every group has two effects (FX) to manage the distribution, and 'encoder' and 'decoder'. The 'encoder' FX is shown below.

Sources 1 and 2 are the left and right signals from the mix received from all the tracks in a group. They are placed on the left and right of the audio space, but it can be moved so that the distribution is different. After this encoding process, the result has to be decoded to any of the speakers configurations described above. Therefore, an 'encoder' FX is used after the decoder. You can find below an image for the decoder used for the 'floor ring'.

The decoders configurations are found in the audio PC under "Desktop/TEMPLATES/REAPER TEMPLATES" or can be downloaded here. The session file already save this configurations, so it is not necessary to load them unless you want to use it independently for other purposes.

Note that you can combine (mix) the three last groups so that it covers the whole room with all the available speakers.

For specific spatial audio applications check the 'Spatial Audio Setup' session later in this document.

Simultaneous Recording and Playback

If a recording and playback should be performed within the same Reaper session, a template file called 'recordingAndPlaybackSession.rpp' can be found in the audio PC at "Desktop/TEMPLATES/REAPER TEMPLATES" or can be downloaded here. This session is shown below and is basically the combination of the recording and playback sessions mentioned before. You can copy this template and adjusted according to your needs.

Spatial Audio Setup

The default configuration for a spatial audio application can be used in either MAX/Msp or Reaper. It is necessary to know the speaker's placement in the room as shown in the 'Speaker Setup' section above in order to build an ambisonic decoder.

There are already default configuration files for decoders. For MAX/Msp in the folder "Desktop/TEMPLATES/MAX TEMPLATES" you will find a max patch called 'spatializer.maxpat' (or it can be downloaded here) which allows to send an input signal to be placed in space according to Cartesian coordinates. This input signal is played through the 24 speakers' array by using the SPAT library. It is already configured with the placement info given in spherical coordinates (azimuth, elevation, distance) according the file 'cartesian-spherical-calculations.xlsx' mentioned previously. The file in MAX indicates how to change this setup if needed.

As a default configuration for Reaper, we use the IEM plugins for spatial audio. A default decoder for the 24 speakers' array called 'speakersDecoder.json' can be found in the audio PC at "Desktop/TEMPLATES/REAPER TEMPLATES" or here. This file can be loaded into the 'AllRADecoder' plug-in in a reaper session. There is a default session called 'spatialAudioTestSession.rpp' that uses this decoder and the necessary tracks for playing a 3rd-order ambisonic file (16 channels). You can copy this template from "Desktop/TEMPLATES/REAPER TEMPLATES " or here  and change it as needed. The image below shows the decoder in Reaper using the IEM plug-in. 

Multichannel Recording

The two RME devices can be used together for multi-channel recording. The fixed 8 XLR inputs below the TV-wall in the lab go through the control room patch directly to the external RME Octamic preamp. This is then connected to the UFX+ interface via ADAT (SMUX) for use with the audio computer. The RME UFX+ also allows additional inputs for example 4 mic channels. 

Usually you will use ADAT from 1 to 8, but signals are being sent also through ADAT 9 to 16 in case you want the same signals replicated on those channels. A template on Reaper called 'recordingDefaultSession.rpp' can be found in the audio PC at "Desktop/TEMPLATES/REAPER TEMPLATES " or here.  This session has 5 types of multi-channel recording: Mono (ADAT1), Stereo (ADAT1-2), 4-channel (ADAT1-4), 6-channel (ADAT1-6), and 8-channel (ADAT1-8).

You can copy this template and use the best adjusted to your case or modify it if needed. As a test you can use the Soundfield microphone to record 4 channels of ambisonic (3D audio) input. There is a Reaper session called 'playbackSoundfieldMicSession.rpp' at "Desktop/TEMPLATES/REAPER TEMPLATES " or here. To playback this ambisonic recording properly, just replace the audio file in the example track track (already configured with the right encoders and decoders) and you will be able to hear the recording in the 24-channel speakers array.