By Robin Shore
Upmixing is nothing new. The basic goal is to take stereo audio and convert it to higher channel count formats (5.1, 7.1, etc.) that can meet surround sound delivery requirements. The most common use case for this is when needing to use stereo music tracks in a surround sound mix for film or television.
Various plug-ins exist for this task, and the results run the gamut from excellent to lackluster. In terms of sonic quality Nugen Audio’s new Halo Upmixer plug-in falls firmly on the excellent side of this range. It creates a nice enveloping surround field, while staying true to the original stereo mix, and it doesn’t seem to rely on any weird reverb or delay effects that you sometimes find in other upmix plug-ins.
What really sets Halo apart is its well-thought-out design, and the high level of control it offers in sculpting the surround environment.
At the top of the plug-in window is a dropdown for selecting the channel configuration of the upmix — you can select any standard format from LCR up to 7.1. The centerpiece of Halo is a large circular scope that gives a visual representation of the location and intensity of the upmixed sound. Icons representing each speaker surround the scope, and can be clicked on to solo and mute individual channels.
Several arcs around the perimeter of the scope provide controls for steering the upmix. The Fade arcs around the scope will adjust how much signal is sent to the rear surround channels, while the Divergence arc at the top of the scope adjusts the spread between the mono center and front stereo speakers. On the left side of the scope is a grid representing diffusion. Increasing the amount of diffusion spreads the sound more evenly throughout the surround field, creating a less directionally focused upmix. Lower values of diffusion give a more detailed sound, with greater definition between the front and rear.
The LFE channel in the upmix can be handled in two ways. The “normal” LFE mode in Halo will add additional content into the LFE channels based on low frequencies in the original source. This is nice for adding a little extra oomph to the mix and it also preserves the LFE information when downmixing back to stereo.
For those that are worried about adding too much additional bass into the upmix, the “Split” LFE mode works more like a traditional crossover, siphoning off low frequencies into the LFE without leaving them in the full range channels.
An Easy And Nuanced UI
The layout and controls in Halo are probably the best of I’ve ever seen in this sort of plug-in. Moving the Fade and Divergence arcs around the circle feels very smooth and intuitive, almost like gesturing on a touchscreen, and the position of the arcs along the edge of the scope seems to correspond really well with what I hear through the speakers.
New users should have no problem quickly wrapping their heads around the basic controls. The diffusion is an especially nice touch as it allows you to very quickly alter the character of the upmix without drastically changing the overall balance between front, rear and center. Typically, I’ve found that leaving the diffusion somewhere on the higher end gives a nice even feel, but for times when I want the upmix to have a little more punch, dragging the diffusion down can really add a lot.
Of course, digging a little deeper reveals some more nuanced controls that may take some more time to master. Below the scope are controls for a shelf filter which, combined with higher levels of diffusion, can be used to dull the surround speakers without decreasing their overall level. This ensures that sharp transients in the rear don’t pop out too much and distract the audience’s attention from the screen in front of them.
The Center window focuses only on the front speakers and gives you some fine control on how the mono center channel is derived and played back. An I/O window acts like a mixer, allowing you to adjust input level of the stereo source, as well levels for each individual channel in the upmix. The settings window provides a high level of customization for the appearance and behavior of the plug-in. One of my favorite things here is the ability to assign different colors for each channel in the surround scope, which aside from creating a really neat looking display, gives a nice clear visual representation of what’s happening with the upmix.
One of the most important considerations in an upmix tool is how it will all sound once everything is folded down for playback from televisions and portable devices, and Halo really shines here. Less savvy upmixing can cause phasing and other issues when converted back to stereo, so it’s important to be able to compare as you are working.
A monitoring section at the bottom of the plug-in allows you to switch between listening to the original source audio, the upmixed version and a stereo downmix so you can be certain that your mixing is folding down correctly. If that’s not enough, hitting the “Exact” button will guarantee that the downmixed version matches the stereo version completely, by disabling certain parameters that might affect the downmix. All of this can be done as you’re listening in realtime, allowing for fast and easy A-B comparisons.
Nugen has really put out a fine well-thought-out product with the Halo upmixer. It’s at once simple to operate and incredibly tweakable, giving lots of attention to important technical considerations. Above all it sounds great. For mixers who often find themselves having to fit two channel music into a multi-channel mix you’ll be hard pressed to find a nicer solution than this.
Halo Upmixer retails for $499 and is available in AAX, AU, VST2 and VST3 formats.
Robin Shore is a co-owner and audio post pro at SilverSound Studios in New York City.