In the past, we have covered upmixing from stereo to 5.1, 7.1 and immersive formats like Dolby Atmos. In this article, we demonstrate how to upmix both stereo and surround examples into 3rd order Ambisonics using Penteo 16 Pro from PerfectSurround and Halo Upmix with the 3D Extension from Nugen Audio.

We have ambience and music examples that you can both listen to and download to compare for yourself how these two upmixing plugins perform when delivering Ambisonic immersive audio files. However, before we get into the ‘how’, we and going to look at the ‘why’.

Reasons For Upmixing To Ambisonics

In recent years the amount of content is being filmed with 360º cameras has been on the rise. As a result, ambisonics audio, which has been around since the 1970s, has found a new purpose, providing immersive soundtracks to go alongside 360º video. In addition, there are an increasing number of VR experiences, games and apps that require immersive audio in which Ambisonics can play an important role. The good news is that several DAWs now support Ambisonics audio, and a growing number of plug-ins now support the format too.

Tools like the Facebook360 Spatial Workstation enable you to work with stereo recordings in one of two ways. The first is to place the stereo sound somewhere within the soundfield, which follows the viewer's head movements. This method works well for sounds attached to an object but doesn't provide a fully immersive sound, which can be beneficial for music or ambient sounds. Alternatively, it's possible to place music and other elements in the stereo headlocked track, however, this means they don't respond to the viewer's head movement.

When using surround recordings in Ambisonics productions, the Facebook360 Spatial Workstation gives options for these to be part of the Ambisonics soundfield. However, as with stereo recordings, no additional spatial information is added, so lacks the fully immersive experience that you get from using Ambisonics recordings.

It may have been the case that the production used a portable sound recorder alongside the 360º video camera. A lot of these only record in stereo, but some models allow a form of surround recording as well. Using these plug-ins enables such recordings to be used to their maximum potential during the post-production stage of a 360º video.

With this in mind, Halo Upmix with the 3D extension, and Penteo 16 Pro have options to upmix to either first, second, or third-order Ambisonics, catering to the growing needs of post-production audio for 360º videos and VR. Using such plug-ins enables you to maximise the usage of existing location recordings, as well as sound effect libraries, in 360º videos and VR experiences which require a fully immersive soundtrack.

The Recordings

In this first set of tests, I'm using stereo recordings made on a Sony PCM-D50 portable recorder. These recordings are from 2008 in Ljubljana, Slovenia, and the first recording is of a group of singers and an acoustic guitar in a church. This recording contains a lot of reverberation, and although recorded in less-than-ideal circumstances, this means there's a significant amount of spatial information that potentially can be upmixed to create an immersive soundfield.

The second recording is people talking and walking out on the street, and again there is a lot of movement and varied placement of the sounds in it, making it an excellent test for the plug-ins to see how they place the various sounds.

The first recording used for the surround tests originated as a double mid-side recording by Mike Thornton, using Sennheiser microphones, which was converted to 5.0 surround ready for upmixing in the plug-ins.

For the second test, a Sennheiser AMBEO mic was used to capture a location sound recording of street ambience, Although this is a first-order Ambisonics microphone, a 5.0 surround version was used in this test, which removed all existing height information.

We Recommend You Listen On Headphones

Since the videos and audio examples are played back in stereo and some example audio is 5.0 surround, they've had to be encoded to binaural. This process used the Facebook360 Spatial Workstation and Ambi Head HD, and the original 5.0 recordings are also available to download for use with demos of these plug-ins.

Nugen Halo Upmix with the 3D extension

In 2017, Nugen released the 3D extension to their popular Halo upmix plug-in. It is now possible to upmix to immersive formats, such as Dolby Atmos, Auro3D, and Ambisonics. The UI is essentially the same as the standard version of Halo, with added controls for vertical distribution. The description of these controls is taken directly from Nugen's documentation…

“On-phase Vertical. This slider determines the amount of on-phase, correlated signal derived from the planar surround layer, that is distributed to the overhead channels. In general this is the 'core sound' and creates a sense of moving the audio energy upward, whilst retaining the 'space' in the planar surround layer.

Off-phase Vertical. This slider determines the amount of off-phase signal that is distributed to the overhead channels, ie. Signal derived from the planar surround layer with a correlation of less than 1. In general this contains a greater sense of 'ambience' and can be used to add air or space into the vertical distribution.”

There are also controls for excluding the Center and LFE channel from the vertical distribution, and a shelf for the overhead channels.

We have uploaded the original stereo recordings, as well as the upmixed results after processing through Halo. There are 3rd Order Ambisonics files as well as versions encoded to binaural through Ambi Head HD.

PerfectSurround Penteo 16 Pro

Towards the end of 2019, PerfectSurround released the latest version of their popular Penteo upmixing plug-in, Penteo 16 Pro. It supports upmixing to various immersive formats, including first, second, and third-order Ambisonics in either AmbiX for FuMa channel orders.

There are several ways to control how the sound is upmixed, and some of these have various settings you can use. The following descriptions are from the developers own documentation…

“Center Channel Modes. Penteo provides three different modes for how sound energy is processed to the center channel:

Default. A good general purpose setting for the center channel where the discrete energy partly replaces the phantom center provided at the input.

Discrete. Creates a totally discrete center channel. Ideal when the level or position of the mono content may need later adjustment. Phantom center is completely eliminated with the faders at zero. If the C Fader is pushed beyond 0dB, slight anti‐phase phantom center is added for a narrowing effect (use with caution). Backing off to a negative setting puts back some of the original phantom center.

Composite. A more subtle center energy setting where front L and R outputs differ from the input in level only. Particularly suitable for "set and forget" use or when surround channels might be lost further down the processing chain. In this mode, the C fader is cross‐linked to the Lss‐Rss fader.

Boost. Increases the energy in the side surround channels by reducing some energy from the rear channels. Boost is ideal for some sound source types when the user wants to reduce the energy from the rear channels. This can have the acoustic effect of moving the rear channels forward, better connecting them with the front sound stage.

Overhead channel modes:

Low: Contains low, ambient energy in the upper channels, favouring center (on‐phase) energy in the bed and off‐phase energy in the upper channels with a slight high‐frequency boost. Low mode is best used to create subtle vertical effects and is excellent when used on high‐frequency, transient sounds.

Raise: Medium, balanced energy in the upper channels ‐ still favoring center (on‐phase) energy in the bed and off‐ phase energy in the upper channels with neutral high‐frequencies. Best to push more sound into the upper channels while maintaining a higher correlation to the bed. Raise mode is useful when the user wants to create a greater size of the overall 360-degree soundfield around the listener.

Max Lift: High energy in the upper channels ‐ keeping off‐phase energy in the bed while favoring center (on‐phase) energy in the upper channels with a high‐frequency boost. Max Lift is best used when a strong more intense emphasis to the overhead channels is needed.”

Again, we have uploaded the original stereo recordings, as well as the upmixed results after processing through Penteo 16 Pro. There are 3rd Order Ambisonics files as well as versions encoded to binaural through Ambi Head HD.

Conclusion

Rather than give my detailed thoughts and opinions about each plug-in, I suggest you download a demo of each and try it for yourself. All I will say is that during my time using and testing these plug-ins I couldn't say there's an overall winner, and upmixing various content makes it clear there's room for both in my workflow. The following plug-ins were used in these tests…

• Halo Upmix with 3D extension () £489 / $699 / €594 (all prices exclude VAT/sales tax.)

• Penteo 16 Pro $499 (excluding VAT/sales tax)

• Ambi Limiter HD €169 (excluding VAT/sales tax)

• Ambi Head HD €189 (excluding VAT/sales tax)

• Facebook360 Spatial Workstation Free