Review: Nugen Audio Halo Upmix

Simon Allen travels to the Hertfordshire HQ of PMC – generous provider of a 5.1 system and demo room for this review – to test out this new mixing tool for film and TV post-production.

Obviously, if a 5.1 mix is required, we’d all much prefer to purposefully create one at the mixing stage. However, this isn’t always possible, for a number of reasons, most common of which is there isn’t the time and budget, or the source material doesn’t exist as stems or in multichannel form.

These ‘upmix’ plug-ins are becoming more abundant, but each has their own strengths, and let’s be honest, often some issues. The problem is simple: trying to create more information from what you started with, for example how to either place music and sound effects in your surround environment, or focus elements centrally, such as dialogue for the big screen from a stereo mix?

Once you’ve created your surround sound, there can then be other issues to consider. For example, how will the new surround mix downmix to stereo again? As most of us know, often the stereo mix, which most domestic systems play, is actually the 5.1 downmixed. Therefore, all this processing can leave the final stereo mix that is heard by the listener a long way from your original stereo mix as you intended it. I set out to find if Nugen’s first release of a solution to this problem could turn out to be as renowned as the company’s measurement tools.

In The Lab

In order to make this review, I was offered one of the 5.1 demo rooms at PMC’s headquarters in Biggleswade, UK. This was great as it avoided installing a system elsewhere. Utilising the surround demo room equipped with some of the best monitoring available meant these were ideal conditions.

I used a complete twotwo system, with twotwo8s along the front for LCR, twotwo6s (pictured, below) for surround and a sub2 for the LFE. The full range of the twotwo8s with their great bass extension meant switching between having the sub2 in the game or not was very transparent. It sounded great, so thanks PMC!


The layout and choice of colours that Nugen has used for Halo look great and feel professional at the same time. The focus of the design being the sound scope actually works very well. Although I don’t usually get on with visuals like this, the way that the real-time display of the sound is sitting in the surround field is accurate, and gives you a sense of confirmation when you’re still working on some settings.

There are generally more user definable parameters than other similar plug-ins, and too many to explain one-by-one in this review. Immediately you can tell this is an all-inclusive tool, and I would recommend spending some time with it before implementing it on a job.

The first most obvious setting is your destination mix type. Used to select between 5.1, 7.1, LCR and virtually any number in between, such as 4.0 or 3.1, Halo covers most types of surround sound format. Once your desired output format is in place, you can see the appropriate outputs displayed around the surround scope and their output meters at the bottom of the window. By default, any speaker or pair of speakers can be soloed from the surround scope, or muted from their retrospective meter. Although you can configure it any way you prefer, this default works well and is very intuitive.

Panning your stereo sound in the surround field is achieved by a couple of arcs. Ultimately this sets how much of your original stereo track is sent to the surround and centre speakers. Halo also features an ‘Arc Link’, which enables you to move the panning as one, in order to affect the overall ‘size’ of the sound.

The arc for the centre speaker, aka the ‘Divergence’, allows some of the extracted content that Halo has identified as centrally panned in the stereo field, back into L and R rather than isolating it in the centre speaker. Therefore, with this arc set to hard centre, Halo will isolate as much content as possible from the stereo image that sits centrally, and push it through the centre speaker. This can be further enhanced with the advanced settings for dialogue rich content, to try and place the dialogue through the centre speaker as you would expect to find in films.

There is also a ‘Diffusion’ setting, which controls the definition of the upmix. With high values of diffusion, the idea is to have a smoother sound that is less focused, i.e. the sound is more spread out in the surround field. With lower values of diffusion, there should be more detail particularly in the front speakers, and it should sound more focused.

When going with higher levels of diffusion for a well-balanced surround experience, another great trick Halo has to offer is a rear shelving EQ filter. This means that by dulling down the top end clarity of the surrounds, the details can remain at the front and the surrounds don’t become distracting.

The way you work with the LFE channel is well thought out. Typically, downmixes into stereo omit the LFE channel. Therefore, the default mode in Halo is to ‘add’ some of the low frequency content through the LFE channel at a reasonably low level. This means you can supply some information to the LFE channel that should help some surround systems that don’t have full range satellite speakers to sound balanced, or simply to make it more exciting. However, if you know your downmix will consider the LFE channel, or you’re not interested in the downmix for certain applications, then Halo also offers a ‘Split’ function. As you’d expect, this operates more along the lines of a typical crossover, where the low frequency energy only exists in the LFE channel.

One key feature you would expect to find on an upmix plug-in such as this is a downmix preview. The calculations for the downmix can be manually set, but the default is based on the typical method. It is obviously important for most 5.1 or 7.1 mix engineers to check how the mix is translating to stereo, and Halo offers a very quick and accurate way of doing this. What’s more notable however is the ‘Exact’ feature. This doesn’t actually change the processing of the upmix, but simply locks out features from the user that have an impact on the downmix compatibility. As you would expect, Halo also offers standard parameters such as channel levels and output channel ordering, making this a very comprehensive tool.

It felt like high values of diffusion pushed the ‘room’ sound to the back and at lower values, the room sound ‘returned’ to the front. It’s very smart, working in-line with the individual reverbs and spatial effects from each stereo mix I presented it with. I found that in most cases some level of diffusion was needed, otherwise the content in the rear didn’t seem rich enough. Most of the time, diffusion levels over 50% were the most desirable.

One very useful feature of Halo was the centre LF split. If you are trying to create a very centre-heavy upmix, perhaps with dialogue, then there is the risk of the centre channel clipping. To help avoid this, Halo can move some of the low frequency content to the L and R channels. This provides a much more efficient and balanced upmix, which will still downmix successfully.

For me, the big news regarding the sound quality of Halo is the fact it identifies and extracts locational sounds in real time. This extends the stereo field without adding any reverb, chorusing or delay so that the downmix is very close to the original mix. In fact, especially with the ‘exact’ feature enabled, it was quite astonishing how extreme the surround image could be; yet the downmix was almost identical to the original.

A couple of other operational functions should be noted. Firstly, as this plug-in can be used in real time without the need to identify a spatial environment, features such as the dialogue separation into the centre channel can be fully automated across a program. This allows a more accurate and interesting sound field to be created as the content changes. I was also particularly impressed with how well loudness translated between the stereo mix and the upmix.

I typically like to avoid using presets, especially when testing plug-ins, but in this case the use of presets is very helpful. There aren’t too many to chose from, but they certainly guide you into using the plug-in in ways you might not have thought possible, or at least take you 90% of the way in one step. For example, Halo can create a large cinematic feel, or a more engaging musical approach via its many parameters.


Nugen has released a very professional product with Halo right from the onset. The parameters are surprisingly flexible, offering many different effects and solutions for a single stereo file. The quality of the processing is generally very pleasing, and competes very highly against other solutions. I can see future updates from this highly reputable manufacturer will not only ensure Halo remains at the top of the upmix game, but will continue to push the boundaries.

Key Features:

Available in AAX, VST and AU formats
Exact downmix matching
Precise centre channel control
Performs powerful real-time analysis of original stereo material
Neural network dialogue isolation

RRP: $449 (until 31 October)

Simon Allen is a recognised sound engineer and pro audio professional with over a decade of experience. Working mostly in music, his reputation as a mix engineer continues to reach new heights.