Stereo Imaging plug-ins, often referred to as stereoisers, use psycho acoustic principles to spatially enhance audio, in short, these types of plug-in transform mono audio tracks into wide and luscious sounding stereo tracks. Over the years I've used stereo imaging plug-ins to enhance a variety of mono tracks. My typical stereoiser plug-ins application are:

• Creating natural sounding stereo acoustic guitars from mono tracks recorded with a single microphone
• Creating deep synth parts
• Sitting single background vocals behind lead vocal parts
• Creating width to mono effect tracks such as delay

There are quite a few different ways in which stereoiser plug-ins can produce realistic sounding stereo content from mono source tracks. There are a number of third plug-ins available that make the stereo imaging process easy to apply to any track in a mix. This article lists a selection of stereoiser/stereo imaging plug-ins that I've used over the years to transform mono tracks into rich-sounding stereo tracks. Before and after audio examples, mono compatibility opinions and examples of my typical applications for each plug-in are also included.

Little Microshift Plug-in By Soundtoys

Many years ago Soundtoys ran a short promotion that enabled users to download the Little Microshift plug-in for free, it was during this promo I downloaded my copy. The current version of Little Microshift looks slightly different in design but features the same controls and from what I understand the same sonic characteristics as well. The Little Microshift creates the stereo width effect by processing audio using a blend of pitch shifting and delay. There are three different flavours of the effect that to my ears sound very similar. Truth be told, I only use the first effect colour and dial in the intensity of the effect to taste with the Mix control. This is a very simple plug-in to use and the results are very pleasing if used sparingly.

Mono Compatible? Yes, to a point though. Extreme amounts of this effect do sound similar to modulation effects rather than stereo widening. When monitored in mono listen to make sure the effect doesn't sound too "Chorus like" if only a small amount of widening was desired.

NUGEN Audio Stereoizer 3 Plug-in

At first glance, you would be forgiven for thinking that the NUGEN Audio Stereoizer would be a complicated plug-in to use, it's not. Don't get me wrong, the NUGEN Audio Stereoizer does perform a lot of magic in the background but the design of the UI has been presented in such a way that makes this plug-in easy to dial in natural sounding stereo width from mono source tracks. There are two algorithms that Stereozier features:

• Inter-aural Intensity Difference (IID):  Difference in volume levels between the left and right channels.
• Inter-aural Time Difference (ITD): Differences in time of arrival between left and right channels.

Both these processes can be workings at the same time within the plug-in, this produces some rather interesting effects, especially on synth parts.

• Free Tutorial - How To Add Stereo Width To Mono Synth Tracks Using Stereoizer By Nugen Audio

I find this plug-in performs really well in IID mode when stereoising organic mono instruments such as acoustic guitars. Setting the IID mode within the upper frequencies ranges really helps mono acoustic guitars sound as though an XY configuration was used to track the guitar.

Mono Compatible? Yes. Stereoizer by NUGEN Audio does a fantastic job of creating natural sounding width without any of the audible artificial downsides.

Stereo Savage Plug-in By Plugin Boutique

Stereo Savage by Plugin Boutique is very much a swiss army knife of stereo enhancement plug-ins. This plug-in features four different stereoiser programs that produce very different stereo imaging results:

• Vox: Users can set a value of detuning to produce stereo width
• Delay: Users can set a delay value between -40ms to +40ms to widen sound
• Expand: Users can set an amount of early reflections to produce stereo. The results sound similar to room reverb.
• Split: Mono sound is split into multiple frequency bands. These bands are panned left and right.

Mono compatible? It depends on the program you are using and the intensity of the effect. Stereo Savage features a very useful Bass Bypass control that enables users to set a frequency point between 50Hz - 8KHz that simply bypasses the stereo imaging effect below that point. If you hear mono compatibility problems then this features makes it very easy to fine tune the effect to fix any issues.

• Pro Tools Expert Video Review - Stereo Savage By Plugin Boutique

Waves PS22 Stereo Maker Plug-in

The PS22 Stereo Maker plug-in is a set of three separate stereoiser tools by Waves:

• PS22 Spread: This plug-in produces stereo width by spreading frequencies across the stereo image (see image). Spread includes an LFSpread control that helps to widen or narrow bass frequency range width.
• PS22 Split: This plug-in doesn't feature the LFSpread control, instead a frequency point can be set and the lower end width is narrow by default. The shape of the frequency spread can be altered.
• PS22 XSplit: This plug-in is a variation of PS22 Split.

This plug doesn't delay audio nor detuned to produce stereo width. Instead, PS22 uses a variety of frequencies evenly across the spectrum to trick the ear into perceiving width. I prefer using the Spread plug-in within the PS22 suite as I like to have control over the bass width. This is a very useful plug-in for adding width to mono effects such as delays.

• Free Tutorial - How To Add Stereo Width To Mono Delay Effects Using Waves PS22 Spread Plug-in

Mono Compatible? When I use the PS22 Spread plug-in to stereoise mono delay effects I don't really notice if I'm having mono compatible problems as the stereo effects I produce with the PS22 is only ever meant to be subtle.

Pitch II

Pitch II is a plug-in that's bundled free with Pro Tools. This can be used to widen tracks if the Pitch II (mono/stereo) instance is used by following these steps:

• Unlink the Pitch Shift L and Pitch Shift R as these two modules are linked by default
• Detune the Pitch Shift L between -10 to -5 cents and sharper the Fine tune of the Pitch Shift R by the opposite + amount.

This is a simple and free way of creating stereo width from mono tracks in Pro Tools. I've find I get more natural results when using this setup in an effects return so that I can blend back some of the original mono signal.

Mono compatible? This depends on how much detuning is applied. If the left and right delays are being used to further the effect then phasing problems can occur in mono foldback - again depending on the values set.

• Understanding The New Avid Pitch II Plug-in

Ozone 7 Plug-in - The Imager Module By iZotope

My first third party plug-in purchase for Pro Tools was iZotope Ozone 3. Ozone 3 featured a Multiband Stereo Imaging module, it was this very module that introduced me to the whole stereo widening process. The Ozone plug-in has developed over the years but it still features an Imaging module at the core of its feature set. Like the Imager in Ozone 3, Ozone 7's Imager is presented in a four band multiband compressor layout. The widening results are clean but can get extreme if care isn't taken. The Imager defaults the lowest band crossover position at 140Hz which I feel is a great place to leave that band as it really isn't worth widening low sub frequencies as the results sound flabby. Creating stereoness from mono audio needs to be a gentle process so that natural results can be produced. The three other bands being low mid, high mid and high can easily be set with each band featuring a control for Width. Tip: Try to not overcook the Stereoize slider as the results can start to sound too unbalanced. I set the Stereoize slider at values below 10.

What Stereo Imaging Plug-ins Do You Use?

Those are a selection of stereo imaging plug-ins that I have used over the years to transform my mono audio tracks into natural and realistic sounding stereo audio. I am fully aware that there must be a handful of plug-ins similar to these six that I haven't come across so please share your processes and stereoiser plug-ins that you use to get your mono tracks sounding stereo.