It's 'Parametric Distortion Filter', just in case you were wondering, and a quick look at Stone Deaf's user list hints at what we're dealing with here - Chris Shiflet (Foo Fighters), Josh Klinghoffer (RHCP) and Josh Homme (QOTSA/Them Crooked Vultures)…
But what does it do? Well, the PDF-1 gives you up to 20dB of volume boost (height) with a parametric EQ filter (freq) that sweeps 65Hz to 3KHz.
The bandwidth control is a five-position switch that focuses the point of the frequency sweep from wide (fat) to narrow (thin). The clean/dirty switch offers you a medium, fuzz-tinged distortion in the latter position and finally, in addition to the main output, there is an uneffected aux out to send a clean signal to a separate amp: useful.
Inside we have a quality 3PDT true bypass switch, a dual-stacked pot for 'freq' and generally high build quality.
If you want a basic, no-brainer distortion, this is not it. The EQ and filtering controls on the PDF-1 offer a colossal breadth of tones many of which, in isolation at least, can sound pretty terrible.
The point of all this tweakability is that it enables you to fine tune your sound to really sit perfectly within a mix, or indeed leap out from it at a specific frequency range. You can have thin, pseudo transistor radio sounds, rasping edgy grind and vocal wah-like sounds.
The more you put the bandwidth towards thin, the more pronounced the effect of the filter, so all the way over to fat is where you'll find the full blooded tones. Any of them will fit right in with the bands named above.
This is a very different take on a distortion/boost, aimed at rock players who want to get their sound dialled in perfectly to a band mix. It has all the filter flexibility you need, with clean boost and an optional edgy rock distortion sound. We like.