With the ability to aim virtual microphones and craft an immersive 360 VR experience, Spatial Mic lends the possibility for great flexibility. In this article we will explore a live concert recording created with Spatial Mic.
Take a listen to Dreamers’ Circus performing ‘Prelude to the Sun’ — a nordic folk remix of Bach’s Violin Partita No. 3 in E Major. This live concert recording was captured with a single Voyage Audio Spatial Mic at the Conrad Prebys Performing Arts Center in La Jolla California.
The 8 channels of audio from Spatial Mic have been decoded to coincident supercardioid microphone patterns at a 90 degree angle for this recording. Later in this article we will learn how to change the pattern. To experiment and listen to the recording in its un-mastered, raw state, first download either the Pro Tools (Ultimate is required) or Reaper DAW session below, along with Spatial Mic Converter plugin (AAX and VST3). The audio in these sessions is uncompressed 24-bit / 96 kHz, so may take some time to download.
The Setup
As we discussed in a previous article, techniques for capturing live concerts can vary wildly depending on the genre of music, concert space, gear available and experience of the recording engineer. With limited microphones, there is a trade-off between direct sound from instruments and diffuse reverberant sound from the room. The distance at which the diffuse sound and direct sound are equivalent is sometimes referred to as the ‘critical distance’ or ‘diffuse field distance’. When recording an ensemble with Spatial Mic, it is important to understand how the mic will react at different distances from the performers and position the mic accordingly.
As you can hear, the mic was positioned by audio engineer Matt Birchmeier in such a way that the final outcome produced a pleasant balance between the direct sound from the performers and the diffuse field of the room in which it was captured. The location of Spatial Mic can be seen right in the middle of the picture below, in front of Dreamer’s Circus and as you listen, see if you can hear the violin player move in the soundfield as the musician moves on stage.
Spatial Mic can be connected to a laptop via a USB to Ethernet extender, which can allow for 200ft of separation. Using this method, the analog mic gain can be controlled remotely from the laptop using the Spatial Mic Control app, while 8 channels of audio is recorded directly into Reaper at 24-bit / 96kHz.
Exploring The Recording
Once you’ve downloaded the session above, you can experiment with decoding the recording to different formats. Go ahead and open the session. In this case we are looking at the Reaper session as shown below:
As you can see in the Spatial Mic Converter plugin window, the default decode is the same Supercardioid Virtual Microphone pair used for the SoundCloud clip. The Stereo audio from the SoundCloud clip has been mastered after rendering this stereo audio.
There are many presets available to listen in different virtual mic configurations. Go ahead and use the preset drop down menu and select from different options. Here is the location of the presets in Reaper:
The presets available are as follows:
Using these presets as a starting point, go further and see how changing the virtual mic parameters ‘Type’, ‘Pattern’ and ‘Width’ change the sound. Use the Rotation, Tilt and Roll to aim these patterns in different directions.
If you’d like to dive deeper into the controls and also learn more about In-Phase, Basic, max rE and Figure 8 patterns, check out this article on the Spatial Mic Converter plugin.
Ambisonics, ATMOS & Surround
With the original recording you can decode to any format you wish. Let’s take a look at some common formats and how to decode.
Ambisonics
The Spatial Mic Converter plugin can output 1st (4 channels) and 2nd (9 channels) order ambisonics in FuMa and ambiX weightings. Most modern plugins use ambiX, especially for higher orders, however there are plugins like the Ambisonic Toolkit that use FuMa weighting.
Simply setup the output section to match the next plugin in the chain. For example, to decode ambisonics to stereo binaural, place a binaural converter directly after Spatial Mic Converter.
Here are some plugin bundles that contain binaural decoders:
- IEM BinauralDecoder (Up to 7th order ambiX ; VST)
- SSA Monitor (Up to 7th order ambiX; VST & AAX)
- FB360 (Up to 3rd order ambiX ; VST & AAX)
- Waves Nx (1st order ambiX ; VST & AAX)
- ATK Binaural Decoder (1st order FuMa ; JSFX for Reaper )
Here is Spatial Mic Converter and SSA Monitor setup for binaural decode:
Ambisonics can also be decoded to different speaker arrays and setups using decoders from various plugin manufacturers.
ATMOS
In a previous journal article we learned how Lenny Jones (Ancient Aliens, Curse Of Oak Island, Unsolved Mysteries) delivers sound effects in Atmos 7.1.2. Let’s take a closer look at the various ways in which this can be done.
To decode from Spatial Mic Converter 2nd order ambisonics output to Atmos 7.1.2 there are different approaches you can take. They all require a DAW plugin to be inserted between the Spatial Mic Converter plugin and the Dolby Atmos Production Suite plugin. Keep in mind that Atmos Production Suite requires Pro Tools Ultimate and only works on macOS.
Here are a few options to convert from Spatial Mic Converter Plugin to Dolby Atmos:
- Blue Ripple Sound ATMOS decoder. This plugin is Pro Tools compatible and accepts up to 3rd order ambisonics, so put the 9 channels from Spatial Mic Converter plugin into the first 9 slots and then leave 10-16 silenced.
- Harpex. Another Pro Tools compatible plugin. Route the first 4 channels from Spatial Mic converter plugin output into the plugin. Even though only 1st order ambisonics is used, the spatial resolution will be higher from the 8 capsule Spatial Mic array than other 4 capsule 1st order microphones.
- Use the Sparta Compass Decoder or IEM ALLRAD Decoder, both of which are free but not available as AAX for Pro Tools. Using one of these plugins, render 7.1.2 in a separate DAW like Reaper and then bring the resulting files into Pro Tools Ultimate for conversion with the Dolby Atmos Production Suite.
Surround
If you’d like to listen on 5.1, 7.1 or other channel based surround formats you can use some of the same tools we looked at for Atmos like Harpex and the Blue Ripple Sound decoders. Blue Ripple Sound also has a free 03A Core plugin suite that includes a 5.1 Basic decoder. The difference is that you will not need to use the Dolby Atmos Production Suite, but rather use the output from these plugins as your speaker feeds.
A quick way to audition channel based formats is to use the Sparta ambiDec or compass_decoder plugins. These are both free VSTs included in the Sparta plugin installer. The Sparta website describes ambiDec is a “A frequency-dependent loudspeaker ambisonic decoder (up to 7th order) with user specifiable loudspeaker directions (up to 64)” while the compass_decoder uses a parametric approach up to 3rd order. Here is a setup with ambiDec showing the various decode presets available:
Going Further
As you can see there are many approaches to decoding. Beyond the methods we covered in this article, other third party tools like SPAT Revolution from Flux include options for advanced panning techniques and loudspeaker configurations.
Do you have a favorite method to decode spatial audio? What method or virtual mic pattern sounds best to you? Let us know
Finally, a big thanks to Dreamers’ Circus ( http://www.dreamerscircus.com) for letting us use this recording and to Matt Birchmeier (http://www.mattdbirchmeier.com) for making this happen.
