Conceptually, Duoflux may be very straightforward, but it’s capable of producing some lovely results! It comprises two modulation engines, each of which is fed separately, according to the chosen Left/Right, Mid/Sides, Low/High or Quiet/Loud settings (there’s a variable crossover frequency for the two‑band Low/High mode). Each engine offers a tape emulation stage, with controls for saturation, wow, flutter and noise, as well as a modulation section. Each section also offers a Lock button so you can retain its settings when changing presets, which is a nice touch.
The plug‑in supports any sample rate used by your Mac/Windows DAW, and also supports up to 8x oversampling — though I found the plug‑in to sound perfectly clean and musical in standard mode. All the usual plug‑in formats are supported, and authorisation is via a personalised key file that allows you to use the plug‑in on all of your own computers. Updates are always free, and there’s a free 14‑day demo available too.
The two identical modulation sections have continually adjustable LFO waveshapes, which morph through sine, ramp and square waves with variable modulation depth. Either engine can run one of 17 modulation algorithms, with a choice of chorus, ensemble, two rotary speakers, tremolo, vibrato, phaser, high‑pass or low‑pass, where the relevant effects offer a choice of free or sync’ed modulation rates. Master controls set the wet and dry level (with or without a link option), and there’s also adjustment of the overall output level, along with input and output metering.
Rotary controls set the Width, Feedback and Character, the last of those being specific to the currently selected modulation type. For example, if you select chorus, it adjusts the delay time, whereas if you pick a filter mode it controls the resonance. Width adjusts the phase difference between the left and right channels but is disabled in the Left‑Right or Mid‑Sides modes. A spectral display shows the input and output audio spectra and hosts a couple of sliding controls for applying low‑ and high‑cut filters. The additional M‑S, Low/High (split‑band) and Quiet/Loud modes extend the creative possibilities. In M‑S mode, for example, you can apply a flanger to the Sides while keeping the Mid clean, or maybe treat it to an ensemble effect. In Loud mode, the two modulation channels are deployed so that one treats the quieter sounds and the other the louder parts.
When you bypass the plug‑in you get that feeling that something important is missing.
Unless you set a high modulation rate, most of the effects are pleasingly subtle, but they still make their presence felt such that when you bypass the plug‑in you get that feeling that something important is missing. By combining the tape emulation with two different types of modulation, the end result is less ‘in your face’ than using a single chorus or flanger, and I found settings that work well on bell or piano sounds as well as on guitar chords and synth pads. Presets for drums and vocals are also included. If you feel the need for some subtle, classy enhancement, Duoflex will provide it.