Following Sennheiser’s January release of the AMBEO ambisonics mic and accompanying A Format to B format conversion plug-in, Sennheiser has announced the first update of the conversion plug-in. V1.1.2 promises a better “ambisonics correction filter” resulting in improved spatial accuracy and reduced colouration of the sound output. Sonnox Community Award winner Tom Lowe owns a Sennheiser AMBEO mic and has been experimenting with it and a variety of tools ever since. Over to you Tom...
I’ll be comparing the new version (1.1.2) to the original (1.0.3) as well as the new Harpex-X ambisonics plug-in, which now features its own input setting for the AMBEO microphone based on measurements and some reverse engineering by Harpex. Prior to this the only way to convert the AMBEO’s A-format output was with Sennheiser’s own software.
I have also tested the recently released v1.3 of Noise Maker’s Ambi Head product, which now features new HRTFs (Head Related Transfer Functions) to take B-format and create a binaural output. In the latest release, the team at Noise Makers have worked with the Sennheiser AMBEO team to recreate the classic Neumann KU100 binaural dummy-head using the AMBEO VR mic. They have also included an HRTF which emulates the one used by Google when playing back 360 videos from YouTube.
The following software is used and is either free to use, or a demo is available:
- Sennheiser AMBEO A-B format converter (versions 1.0.3* and 1.1.2)
- Soundfield SurroundZone 2
- Noise Maker’s Ambi Head
*this version is no longer available for download from Sennheiser
Specially Recorded Demo Files
I recorded some new material in central London, especially for the test. With various sirens, people talking, building work, and buildings for the sounds to reflect off, I felt this would be a good test of spatial definition and positioning of sound. This was recorded without a windshield to get the purest sound from the microphone. The downside was this requires recording in an area with no more than a light breeze, and certainly isn’t recommended for day-to-day recording with any mic. I used the Zoom F8 multitrack recorder at a sample rate of 96KHz, 24-bit.
Other than the decoding plug-ins, no other processing was used on the audio, and I have also provided the un-processed A-format audio from the AMBEO mic so you can do your own tests. All software was left in default settings, other than changing the input and output formats where necessary.
Once the resulting audio was loaded into Pro Tools, I set up a quad (4.0) audio track for each example and inserted the required plug-ins on each track.
To compensate for output levels differing between plug-ins all examples have been normalised to -30LUFS. Due to the nature of the recording being ambience, -30 was chosen over the more common -23LUFS.
For the Sennheiser AMBEO A-B format v1.0.3 test the following plug-ins and outputs were created:
- AMBEO A-B format converter followed by Noise Makers Ambi Head for a binaural output
- AMBEO A-B format converter followed by Harpex-X for a binaural output
- AMBEO A-B format converter followed by Soundfield SurroundZone 2 for a stereo output
- AMBEO A-B format converter followed by Harpex-X for a stereo output
- AMBEO A-B format converter followed by Soundfield SurroundZone 2 for a 5.1 surround output
- AMBEO A-B format converter followed by Harpex-X for a 5.1 surround output
The session was then saved and v1.1.2 of the Sennheiser A-B converter was installed and the exact same tracks were exported using the new version.
As the Harpex-X plug-in offers its own A-format decoding for the AMBEO mic, I conducted another test using this. This also has the added advantage that only one plug-in was required in the channel, as it handles all processing, and SurroundZone 2 is therefore not required to convert B-format audio to the desired output format.
- Harpex-X AMBEO to binaural
- Harpex-X AMBEO to stereo
- Harpex-X AMBEO to 5.1 surround
The Test Files
We have made all the stereo and binaural files available on a Soundcloud playlist. In addition, you can download all the demo files which include the 5.1 files as well as the stereo and binaural files and the original A format file from the AMBEO mic so you can conduct your own listening lists.
Having exported the audio from the 3 sessions, I then setup a 4th session for easy comparison, and soloed each track. Starting with the conversion from A-format to binaural, my initial thoughts were the updated Sennheiser A-B format converter is a definite improvement. The sound seems brighter, clearer, and the reverb of sounds bouncing off the surrounding buildings seemed more natural. For converting binaural output, Harpex-X was my preferred plug-in. Ambi Head v1.3 is a definite improvement over v1 and has more low-end and lots of depth, however, the spatial localisation in Harpex-X is far more accurate. It also has a brighter top end which doesn’t sound forced or unnatural. Listen out for the motorbike at 1 min 20 seconds to compare the spatial positioning. For a fair comparison, I used the KU100 option which becomes available in Harpex-X when the output is set to binaural.
Next came the stereo output test. In this test, I preferred the output from Harpex-X rather than SurroundZone2, as it seems a little brighter, with more clarity and definition. The improvement with the new AMBEO A-B converter is also still obvious. As in the previous tests, I kept the default settings, other than turning off the high-pass filter, as the AMBEO plug-in was taking care of this. There are a huge number of controls to affect the sound in Harpex-X, far more than what is available in SurroundZone 2, however, the Harpex plug-in costs €498 + VAT, and so more control is to be expected. It may be hard to justify the cost, especially if you only intend to output to stereo or binaural, but for 5.1 and higher channel widths, Harpex-X really comes into its own and is incredibly useful if working in immersive formats such as Dolby Atmos, or any format with height channels. When it came to the 5.1 surround test, I felt Harpex-X gave a nicer sound again, and the additional controls for focusing or diffusing the sound are great additions.
In the final test, just using the Harpex-X to take care of all conversion, I felt the difference even more pronounced than between the 2 versions of the AMBEO A-B converter. There was a definite improvement in definition, and the resulting sound is brighter, but not too hyped. However, for the binaural output, I preferred the result from the second test using the latest AMBEO A-B converter followed by Harpex-X for conversion to binaural. I found using Harpex-X for the whole process gave a lighter sound, which was a little harsh for my liking, as well as sounding EQ’d and a little unnatural.
To sum up, I would say Sennheiser have done great work and v.1.1.2 is a much welcome improvement. If you intend to use recordings from the AMBEO directly in 360 videos with minimal processing, or pass them directly to the Facebook Spatial Workstation, or convert them to binaural, then there is little reason to purchase Harpex-X plug-in. For more complex workflows with Dolby Atmos, Dolby Atmos for VR, or other immersive formats, then the price is easily justified and a good investment. Although I preferred the binaural output from Harpex-X I do feel Ambi Head is a useful tool, especially to test 360 video content destined for YouTube, and for this alone it’s worth the €189 + VAT price tag.