Ambisonic Studio Ambisonic
   
Hybrid Surround
                      Sound Mixing with Nuendo  
 
 

The goal of this article is to provide step by stepinstructions for integrating Ambisonic first order B-Format in a surround sound mix for video or film. If you're not familiar with Ambisonic surround sound technology, we suggest you read this article and this article or the Wikipedia entry first.You must also be familiar with Steinberg Nuendo.

The software used for this demonstration is OS X 10.4 to 10.8, Steinberg Nuendo 3/4/5, David McGriffy Visual Virtual Microphone VST plug-in, Dave Malham & Ambrose Field Ambisonic VST plug-ins and York University Ambisonic VST plug-ins. Apart from OS X, all the software is compatible with Windows OS.

The information on this page is provided as is, without any guarantee regarding performance or end result.

Ambisonic B-Format files can be downloaded from the Ambisonia and the Sound of Space websites. Most of the files available there have a «.amb» extension: if Nuendo can't recognize the files, replace the «.amb» with «.wav».

The Ambisonic B-Format is a multichannel surround sound format that is not intended to be directly played back on loudspeakers. The B-Format stream has to be decoded to a speaker-ready stream (historically referred to as «D-Format»). On the other hand, Steinberg Nuendo, version 2, 3 and 4, handles surround sound audio streams in a speaker-ready fashion. The Nuendo approach is more traditional and is also usually easier to understand. The challenge then with Nuendo is integrating audio streams that are speaker-ready (traditional surround) with audio streams that are not speaker-ready (Ambisonic B-Format) into the same mix. This task is not straightforward, but certainly not impossible. We call this type of surround sound mixing, that integrates traditional surround and Ambisonic surround, hybrid surround sound mixing.

Part of the trick when doing a hybrid mix in Nuendo is «fooling» it into using speaker channels for the B-Format routing. Since most of the Ambisonic VST plug-ins used to process first order B-Format (four channels WXYZ) expect that the four channels will be presented to the plug-in's first four inputs, we must ensure that it will be so with Nuendo. Within its constraints, one of Nuendo neat routing feature is that it will respect channel routing based on channel denomination when going from one speaker setup to another one. For example, if you have a four channel LRC+LFe (L R C Lfe) audio track routed to a 5.1 bus (L R C Lfe Ls Rs), Nuendo will send the audio track to the first four channels of the bus because the channels have the same name: L R C Lfe. This routing will also be facilitated by the use of child busses. These two features, name-based channel routing and child busses, are true for all types of busses: Group Channel, FX Channel and Output.

Here is a compatibility chart between B-Format (four channel) audio track formats and Group Channel, FX Channel and Output busses formats. Using these suggested audio track and bus formats is needed for easier routing.

B-Format audio track   Compatible busses for B-Format
Quadro (WXYZ)   Quadro (L R Ls Rs) / 4 channels
    6.0 music (L R Ls Rs Sl Sr) / 6 channels

 
LRC (WXY)   LRC (L R C) / 3 channels
LRC+Lfe (WXYZ)   LRC+Lfe (L R C Lfe) / 4 channels
    5.1 (L R C Lfe Ls Rs) / 6 channels
    6.1 Cine (L R C Lfe Ls Rs Cs) / 7 channels
    7.1 Cine (L R C Lfe Ls Rs Lc Rc) / 8 channels
    8.1 Cine (L R C Lfe Ls Rs Lc Rc Cs) / 9 channels
    10.2 (L R C Lfe Ls Rs Tfl Tfc Tfc Trl Trr Lfe2) / 12 channels

 

For this demonstration, we will be doing a hybrid 6.1 mix (L R C Lfe Ls Rs Cs). This mix will feature mono audio tracks, stereo audio tracks, B-Format interleaved audio tracks and B-Format split audio tracks.

The Hybrid Surround Sound Mix Nuendo project was tested at UQAM Media School Surround Sound Studio (pictured right) with a 6.1 speaker setup consisting of Dynaudio Air 6 speakers and two subwoofers in the following positions: Left at +30°, Right at -30°, Center at 0°, two Lfe on floor beside Left and Right position, Left Surround at +120°, Right Surround at -120°, Center Surround at 180°.

 

 

1

 

VST Connections

 

In Nuendo, create a New Project. In the Outputs pane of the VST Connections window, create a 6.1 Cine bus, a Stereo child bus and a LRC+Lfe child bus.

The child busses will be used for direct routing of stereo audio tracks.

This demonstration use a Digidesign HD audio interface connected to the speakers according to Nuendo 6.1 Cine setup. So, with our installation, channel names in the output bus correspond to the real speaker locations.

         

2

 

VST Connections: Group/FX

 

In the Group/FX pane of the VST Connectionswindow, create a 6.1 Cine Group Channel bus, four mono child busses (Left, Right, Center and Lfe) and a LRC+Lfe child bus.

This B to 6.1 Group Channel will be used to decode the B-Format to the 6.1 Cine speaker setup. This Group Channel will then be sent, speaker-ready, to the 6.1 output bus.

It's essential to note that the inputs of the B to 6.1 Group Channel, although denominated L, R, C and Lfe, are not receiving such streams. They are receiving, in order, channels W, X, Y and Z of the B-Format.

The mono child busses will be used for direct routing of B-Format split audio tracks and the LRC+Lfe child bus for direct routing of B-Format interleaved audio tracks.

         

3

 

Mixer

 

Add as many mono, stereo, B-Format interleaved and B-Format split Audio tracks as needed. We recommend grouping each B-Format split set into its own folder track for easier manipulation in the Project window.

In the Mix window, assign mono Audio tracks directly to the Center channel of the output bus (in the case of dialogues, for example) or to the whole output bus so you can pan the mono streams using the Nuendo panner.

Assign stereo Audio tracks directly to the Stereo child bus of the output bus or to the LCR+Lfe child bus of the output bus if you want to use the Lfe channel with your stereo tracks.

Assign B-Format interleaved Audio tracks directly to the LRC+Lfe child bus of theB to 6.1 Group Channel bus.

Assign B-Format split Audio tracks directly to the mono child busses of theB to 6.1 Group Channel bus: W to Left, X to Right, Y to Center and Z to Lfe.

Assign theB to 6.1 Group Channel to the 6.1 output bus.

Insert an instance of Nuendo TestGenerator in all audio tracks.

Insert an instance of York's B-Proc in the interleaved B-Format Audio tracks.

Insert an instance of the Visual Virtual Microphone (VVM) plug-in in the B to 6.1 Group channel. Optionally insert an instance of B-Proc in the Group Channel, but before the B-Format is decoded by the VVM.

We recommend some input levels attenuation in the busses: we use -3 dB in this demonstration.

         

4

 

Routing Overview

 

Here is the routing overview of the Hybrid Surround Sound Mix.

         

5

 

Mono
                            Check

 

You can check that the mono audio tracks are going to the Center channel of the output bus with the TestGenerator.

         

6

 

Stereo Check

 

You can check that the stereo audio tracks are going to the Left and Right channel of the output bus with the TestGenerator.

         

7

 

B Interleaved Check

 

You can check that the B-Format interleaved audio tracks are going to the first four channel of the B to 6.1 Group Channel with the TestGenerator.

Leave the B-Proc and VVM plug-ins off if present in the Group Channel.

         

8

 

W
                          Split Check

 

You can check that the W in the B-Format split audio tracks is going to the first channel (Left) of the B to 6.1 Group Channel with the TestGenerator. Leave the B-Proc and VVM plug-ins off if present in the Group Channel.

         

9

 

X
                          Split Check

 

You can check that the X in the B-Format split audio tracks is going to the second channel (Right) of the B to 6.1 Group Channel with the TestGenerator. Leave the B-Proc and VVM plug-ins off if present in the Group Channel.

         

10

 

Y
                          Split Check

 

You can check that the Y in the B-Format split audio tracks is going to the third channel (Center) of the B to 6.1 Group Channel with the TestGenerator. Leave the B-Proc and VVM plug-ins off if present in the Group Channel.

         

11

 

Z
                          Split Check

 

You can check that the Z in the B-Format split audio tracks is going to the fourth channel (Lfe) of the B to 6.1 Group Channel with the TestGenerator. Leave the B-Proc and VVM plug-ins off if present in the Group Channel.

         

12

 

VVM Hexa

 

Activate the VVM insert in the B to 6.1 Group Channel for decoding the B-Format to the 6.1 speaker setup. The VVM allows for total control of speaker feeds in terms of azimuth, elevation and polar pattern of the associated virtual microphones. The decoding we successfully tested is made of cardioids (except the Lfe which is omni or W) with the following gain weighting: 0 dB on Left and Right, -6 dB on Center, -6 dB on Lfe, -3 dB on Left, Right and Center Surrounds. This preset is available here.

         

13

 

VVM
                          Hexa Total

 

As we can see from the Show Total view of the VVM, this setting produces a regular spatial distribution with a slight frontal dominance, adequate in a surround mix for video or film. The choice of cardioids, while lacking in azimuth discrimination, insures that sound objects will never appear in their opposite direction: this is preferable especially for large venue playback where most of the audience is outside the sweet spot.

         

14

 

VVM
                          Routing

 

As a precaution, edit the VVM insert routing (VST Settings of the B to 6.1 Group Channel) so as to stop the Ls, Rs and Cs channels from going through the insert.

         

15

 

VST Settings Routing

 

If the B-Proc plug-in is also inserted in the B to 6.1 Group Channel, you can also edit the insert routing to stop the Ls, Rs and Cs channels from going through the insert.

         

16

 

W
                          Decoded Check

 

With the TestGenerator in the B-Format split channels, you can check the W signal distribution once decoded: as expected, the signal is present in every speaker channel of the 6.1 busses.

         

17

 

X
                          Decoded Check

 

With the TestGenerator in the B-Format split channels, you can check the X signal distribution once decoded: as expected, the signal is most present in speaker channels on, or close to, the X axis of the 6.1 busses. No signal is present in the Lfe because it's fed only by the W.

         

18

 

Y
                          Decoded Check

 

With the TestGenerator in the B-Format split channels, you can check the Y signal distribution once decoded: as expected, the signal is present in speaker channels on, or close to, the Y axis of the 6.1 busses. No signal is present in the Lfe because it's fed only by the W.

Since the Center channel and the Center Surround channel are exactly on the Y null axis (90°-270° relative to Y, 0°-180° relative to X), no signal is present in the Center and Center Surround Channels.

         

19

 

Z
                          Decoded Check

 

With the TestGenerator in the B-Format split channels, you can check the Z signal distribution once decoded: as expected, the signal is absent from all speaker channels since a 0° elevation was specified for every channels.

         

20

 

Project Healey's View

 

Once correct routing has been checked, the mixing can start. Note that B-Format interleaved Audio tracks can receive either four channels complete first order B-Format files or three channels horizontal first order B-Format files. The WXY channels of the horizontal B-Format will be routed adequately to the Group Channel where the decoding is taking place.

         

21

 

Hybrid
                          Mixing

 

By integrating B-Format to a «standard» surround sound mix, the Hybrid Mix allows mixing engineers to keep their usual workflow.

Sound objects that are needed to be in very precise positions, like dialogues or stereo music, can be directly routed to the desired loudspeaker. But the included B-Format recordings, like ambiences, will permit easy sound field manipulations and coherent playback on many speaker setups.

 

Sound field manipulation with Nuendo 3 for B-Format split files

Ideally, B-Format split files are be sent to a LRC+Lfe Group Channel to permit sound field manipulation with the B-Proc plug-in before being sent to the B to 6.1 Group Channel. This can be done with Nuendo 4. But since Nuendo 3 won't allow to send one Group Channel into another, we are limited to few sound field manipulations that can be easily achieved. These manipulations are basically axis rotations in 90° increments and axis flipping.

B-Format manipulation   Polarity and bus assignments (LRC+Lfe)
90° CCW horizontal rotation (Front is Left, Left is Back)   X to Center, Y inverted to Right
90° CW horizontal rotation (Front is Right, Left is Front)   X inverted to Center, Y to Right
180° horizontal rotation (Front is Back, Left is Right)   X inverted to Right, Y inverted to Center
90° vertical rotation up (Front is Top, Top is Back)   X to Lfe, Z inverted to Right
90° vertical rotation down (Front is Bottom, Top is Front)   X inverted to Lfe, Z to Right
180° vertical rotation (Front is Back, Top is Bottom)   X inverted to Right, Z inverted to Lfe
90° tilt to the left (Left is Bottom, Top is Left)   Y inverted to Lfe, Z to Center
90° tilt to the right (Left is Top, Top is Right)   Y to Lfe, Z inverted to Center
180° tilt (Left is Right, Top is Bottom)   Y inverted to Center, Z inverted to Lfe
Front-Back flip (Front is Back)   X inverted
Left-Right flip (Left is Right)   Y inverted
Top-Bottom flip (Top is Bottom)   Z inverted

 

 

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