Ambisonic Studio | B-Format to Stereo UHJ with Nuendo

The goal of this article is to provide step by step instructions for converting Ambisonic first order B-Format three or four channels interleaved audio files to Stereo UHJ audio stream and files. If you're not familiar with Ambisonic surround sound technology, we suggest you read this article, this article or the Wikipedia entry first. You must also be familiar with Steinberg Nuendo.

The software used for this demonstration is Mac OS X 10.4.11/10.5.8/10.6.2, Steinberg Nuendo 3.2.1/4.3.0, Angelo Farina B-Format to UHJ impulse responses, Dave Malham & Ambrose Field Ambisonic VST plug-ins and York University and a convolver plug-in of your choice. Apart from OS X, all the software is compatible with Windows OS.

You can also try the simple Nuendo project (Mac OS X only) with all the appropriate routing and processing done within the B2UHJ plug-in, part of the B2X plug-in suite.

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

People familiar with Ambisonic know about Stereo UHJ: it's a way of encoding first order B-Format into two channels for compatible playback on traditional stereo equipment and for decoding in surround sound with the appropriate Ambisonic decoder. For Ambisonic purists, Stereo UHJ as always been a compromise, but one that can produce a subjective pleasing result when listened undecoded in stereo. As for the need to still encode B-Format in Stereo UHJ, there's arguably less a need to do it nowadays, but the ability is not worthless and the result, not uninteresting.

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

If you don't want to construct the B-Format to Stereo UHJ Nuendo project, here's a Nuendo template.

1				This is the signal processing path for the B-Format to Stereo UHJ conversion that will be followed in Nuendo. Signal processing path and image by Angelo Farina.

2				In Nuendo, create a New Project. In the Outputs pane of the VST Connections window, create two LRC+Lfe output busses. One of them will output the UHJ encoded signal and the other a straight stereo decode for comparative monitoring. Connect only the L & R of both busses to the audio card/interface. You can rename the output busses UHJ and Stereo.

3				In the Project window, add a LRC+Lfe Audio track and three LRC+Lfe Group Channel tracks. You can rename the Audio track B-Format and the Group Channel Tracks W to UHJ, X to UHJ and Y to UHJ.

4				In the Mix window, assign the B-Format Audio Track to the Stereo output bus. Assign the three Group Channels to the UHJ output bus. Since that with this setup every track and bus use the same channel configuration (LRC+Lfe), no panner or Mix Convert instance should automatically appear. Also in the B-Format Audio Track, insert an instance of Nuendo's Mix Delay plug-in. Despite its name, this plug-in can be useful with B-Format tracks to correct levels or polarity of specific B-Format channels when the source is an interleaved B-Format file. Again in the B-Format Audio Track, insert an instance of York University B-Proc.This plug-in will give you the ability to manipulate the B-Format signal. We believe it's important to optimize the B-Format signal for best horizontal surround or stereo playback: this optimization could include the virtual tumbling of the horizontal plane toward the main sound source if the Soundfield type microphone was higher than the sound source. Insert an instance of our three simple B-Format simple routing plug-ins (made with SonicBirth) in the Group Channels: W to LR in the W to UHJ Group Channel, X to LR in the X to UHJ Group Channel and Y to LR in the Y to UHJ Group Channel. Note: you have to install SonicBirth for these three plug-ins to be functional. Also insert an instance of a Stereo Convolver in each of the Group Channels. Insert an instance of York's B-Mic in the Stereo output bus: this will give you the opportunity to compare the Stereo UHJ version to a straight stereo decoding of the B-Format. Optionally insert an instance of a spatial level meter in the UHJ output bus. Waves Paz Position is a good example of such a meter. To avoid saturation and maintain roughly equal levels between the B-Format Audio Track and the Stereo UHJ output bus: we recommend to pad the input of the Stereo UHJ output bus by 3 dB.

5				In the Mix window, turn on three Sends in the B-Format Audio Track, one to each of the Group Channels. The Sends are post fader and at 0 dB level.

6				To test that the Sends are going only to their respective Group Channels, without leaks, and are evenly balanced within their Group Channel, use one of these audio files in the Project window. The files are four channel interleaved 16 bit FLAC file at 44.1, 48 or 96 kHz sample rate with either a 200 Hz or 20000 Hz tone.

7				When playing back the file, the tone in the first (W) channel should be sent only to the W to UHJ Group Channel. The other Group Channels should be totally silent, confirmed by the «minus infinity» measured level at bottom of the faders.

8				When playing back the file, the tone in the second (X) channel should be sent only to the X to UHJ Group Channel. The other Group Channels should be totally silent, confirmed by the «minus infinity» measured level at bottom of the faders.

9				When playing back the file, the tone in the third (Y) channel should be sent only to the Y to UHJ Group Channel. The other Group Channels should be totally silent, confirmed by the «minus infinity» measured level at bottom of the faders.

10				When playing back the file, the tone in the fourth (Z) channel should not be sent to any of the Group Channels. All Group Channels should be totally silent, confirmed by the «minus infinity» measured level at bottom of the faders.

11				Activate the Stereo Convolver plug-ins in the three Group Channels. Load the appropriate impulse response in each (w_uhj_.wav, x_uhj_.wav, y_uhj_.wav**) with the sample rate corresponding to the Nuendo project. Download the B-Format to Stereo UHJ impulses responses.

12				It's possible to visualize the B-Format to Stereo UHJ conversion with the Waves Paz Position plug-in inserted in the Stereo UHJ output bus. With typical musical material that contains a broad range of frequencies, the converted W channel should look like this with Waves Paz Position. Left = 0.5(0.9397W - j0.342W) Right = 0.5(0.9397W + j0.342W) To test this, you can use the pink noise B-Format files available here.

13				With typical musical material that contains a broad range of frequencies, the converted X channel should look like this with Waves Paz Position. Left = 0.5(0.1856X + j0.5099X) Right = 0.5(0.1856X - j0.5099X)

14				With typical musical material that contains a broad range of frequencies, the converted Y channel should look like this with Waves Paz Position. Left = 0.5(0.655Y) Right = 0.5(- 0.655Y)

15				Replace the test tone file in the Project window with the B-Format sound file to convert to Stereo UHJ. This file can be three channel interleaved (WXY) or four channel interleaved (WXYZ).

16				At this point, you can do the following: If needed, activate the Mixer Delay in the B-Format Audio track to correct the sound field with individual channel level changes and polarity inversion. If needed, activate the B-Proc in the B-Format Audio track to manipulate the sound field through rotation or thumbling/tilting. Compare the signal in the UHJ output bus to a stereo decode using the B-Mic plug-in in the Stereo output bus (don't forget to mute/solo one output or the other).

The simple Nuendo project for converting B-Format to Stereo UHJ (Mac OS X only)

It's possible to incorporate all the routing and signal processing needed for B-Format to stereo UHJ within one plug-in, the B2Stereo/UHJ. The simplicity that comes with this encompassing plug-in opens the door to more affordable audio editors that supports more than two track (Audiofile Engineering Wave Editor, Freeverse Sound Studio, TwistedWave) to be used for B-Format to UHJ conversion.

If you don't want to construct the Simple Nuendo project for converting B-Format to Stereo UHJ, here's a Nuendo template.

1				In Nuendo, create a New Project. In the Outputs pane of the VST Connections window, create one LRC+Lfe output busses. Connect only the L & R of the output bus to the audio card/interface.

2				In the Project window, add a LRC+Lfe Audio track. Place the B-Format sound file to convert to Stereo UHJ. This file can be three channel interleaved (WXY) or four channel interleaved (WXYZ).

3				In the Mix window, assign the B-Format Audio Track to the output bus. Since that with this setup the audio track and all busses use the same channel configuration (LRC+Lfe), no panner or Mix Convert instance should automatically appear. Also in the B-Format Audio Track, insert an instance of Nuendo's Mixer Delay or the Correct2B plug-in. These plug-ins can be useful with B-Format tracks to correct level or polarity of specific B-Format channels when the source is an interleaved B-Format file. Again in the B-Format Audio Track, insert an instance of the B2B.This plug-in will give you the ability to manipulate the B-Format signal. We believe it's important to optimize the B-Format signal for best horizontal surround or stereo playback: this optimization could include modifying the virtual elevation of the horizontal plane toward the main sound source if the Soundfield type microphone was higher or lower than the sound source. Insert an instance of the B2Stereo/UHJ in the output bus: this plug-in will give you the opportunity to compare the Stereo UHJ version to a straight stereo decoding of the B-Format.