Given the fairly bold name, you might be forgiven for thinking that MSXII Sound Design's Lo‑Fly Dirt is another take on the overdrive/distortion effect genre (of which iOS has quite a few), but that's not quite what is being offered here. While Lo‑Fly Dirt can make things very grungy, it is perhaps more akin to the analogue saturation plug‑ins that have become very popular on desktop platforms over the last few years. As a music technology company, MSXII have been around for some time and have a large catalogue of sample library products but, on release, Lo‑Fly Dirt represented their first iOS music app. They have since added the very quirky Fly Tape, a tape effects app.
Lo‑Fly Dirt is provided as an AU3 plug‑in only but should run fine in any iOS AU host such as AUM, AudioBus, BeatMaker 3, GarageBand or, as I did with my own testing, Cubasis. Having inserted the plug‑in on a suitable track, the app is simple enough to use. Bottom‑left are the input and output faders (by default, these seem to be set to zero; raise them to hear what the effect is doing), while the large dial that dominates the GUI is a dry/wet knob rather than a gain control. Wound increasingly clockwise, you get 'more' of the effected audio.
In terms of lo‑fi processing, the app offers seven modes, each with a different flavour of lo‑fi treatment. These are arranged along the top of the display and you cycle through them using the Mode button. With none of the virtual LEDs alight, you get the Default mode which delivers a very light saturation effect. This is really rather nice and can be used on almost any audio source. This includes vocals, where a little can add a nice warmth and a lot can give you some grit without things ever going too far.
The rest of the modes — 60, 404 (two different flavours), 1200, 8‑bit and SK‑5 — are generally less subtle. So, for example, 60 mode gives you a 12‑bit‑based sound allied with saturation, compression and a little top‑end EQ. It can be great to make a tame drum machine into a bit of a monster. In contrast, SK‑5 mode provides an 8‑bit sound but adds high‑pass filtering and some punchy compression. Again, you might not use it for a delicate plucked guitar but it works great for aggressive drums or synths. If you want something a bit grittier than the default mode, but less so than the SK‑5 or 8‑bit modes, then the 1200 mode also has that covered; subtle, but not too subtle.
The app is very easy to use and, with the wet/dry option, you can dial in just as much, or as little, as you need. I had no technical issues with Lo‑Fly Dirt in testing and, while this is most certainly a specialist audio processor, given the modest asking price, if you like to experiment with adding grunge to your audio, then this is a simple and effective way to do so.