Creating binaural content with Spat Revolution

Felix Niklasson — Tue, 21 Jul 2020 18:46:49 +0000

FLUX:: IRCAM Spat Revolution is an object-based immersive audio mixing suite that includes a stand-alone rendering and processing application, and a set of plugins for audio and automation integration with various DAW hosts.

Spat Revolution renders virtual environments (Rooms) using a variety of spatialization techniques and panning protocols, and integrates the fundamental channel and scene-based approaches; Ambisonics and HOA.

While rendering to loudspeakers, which often is the final destination, one of the most often-used techniques in Spat Revolution relies on binaural synthesis and the ability to render the source objects, arbitrarily positioned in a virtual environment, to a pair of standard headphones using the same two audio channels.

Binaural takes two forms: First, binaural can be chosen as a stream type in order to virtualize every individual source-object and the room effect (acoustic simulation) of a Spat Revolution room (your object-based mix). This is the ideal scenario when creating content for live streaming, or for bouncing the two audio channels as a binaural deliverable.

Because multiple rooms are supported, some scenarios may include having some source objects connected to a binaural room, while others are connected to a standard stereo room. This strategy enables the mixer to, for example, keep some instruments that are rich in transients, like a kick drum in a stereo pan law, very much locked in between the ears. A simple summation then returns everything together in the headphone mix in the end.

The second form of binaural is binaural monitoring. This makes it possible to audition any channel-based speaker arrangements over your headphones. In this particular case, you are virtualizing each speaker as a source, which is extremely convenient when you don’t have access to the diffusion system you are preparing the content for.

In the two binaural modules in Spat Revolution, Room or Monitoring, there is an option to choose an HRTF. By default the HRTF used is Kemar, though this can be changed in the set up in the Spat Revolution preferences page.

Want to read more?

Read on Getting your Aural ID for binaural reference accuracy and Managing and Importing HRTF.

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Managing and Importing HRTF

Felix Niklasson — Tue, 21 Jul 2020 18:12:44 +0000

Using binaural audio means dealing with HRTFs. In the HRTF section in the Spat Revolution preferences menu, you can access and manage HRTFs. The HRTF used by default is Kemar, which can of course be changed and another HRTF can be set up as default instead.

In the Manage HRTF section you have access to a database listing locally available and downloadable HRTFs. When an HRTF is downloaded, or locally available on your computer, you can set up, with Include or Exclude, which HRTFs are displayed as available in the Spat Revolution Binaural Room or Binaural Monitoring modules.

As an example, the KU100 Neumann HRTF, commonly used in 360/VR pipelines and in VR SDKs (Google, YouTube, etc.), is available in the database and can be downloaded and included in your workflow.

Choosing the KU100 Neumann as the default HRTF will assure it is selected automatically every time you use a Binaural Room or Binaural Monitor module.

If you are fortunate enough to have your own HRTF, you can simply import your file to Spat Revolution in a few simple steps. First, verify that your HRTF is using a SOFA file format and that it’s Diffuse Field Equalized – this means that the direction-independent component in the HRTF is removed. This direction-dependent component is referred to as a DTF (Direct Transfer Function) version. Supported are SimpleFreeFieldHRIR or SimpleFreeFieldSOS IIR. HRTF Modeled as IIR filters are preferred.

Ideally, your file name ends with SampleRate.SOFA. With this file name structure, Spat Revolution will import all your HRTFs as one single entity, with various sample rates available. (Without this file name structure, each sample rate will be imported as a separate HRTF, which is not as convenient. File example “My HRTF name”_44100.sofa “My HRTF name”_48000.sofa :My HRTF name”_96000.sofa)

Importing your HRTF to Spat Revolution will require four simple steps:

1. Locate your files and open Spat Revolution.

2. Go to Preferences, HRTF section, Manage HRTFs.

3. Press the import button and select your .SOFA files (You can select all sample rates).

4. Make sure to choose the DTF version of your HRTF.

Success!

When your HRTFs are imported, you will see them as available files, which from now on will automatically be included in your Spat Revolution software preferences. Your last step is to simply choose your HRTF as the default in the HRTF section in the Spat Revolution preferences.

The post Managing and Importing HRTF appeared first on FLUX:: Immersive.

Managing HRTF Archives - FLUX:: Immersive

Creating binaural content with Spat Revolution

Managing and Importing HRTF