Pigtronix Philosopher's Tone: This new pedal from Pigtronix is an adaptation (and improvement) of a circuit they developed for their Attack-Sustain and Mothership pedals, and they assert it is not based on the same old Ross or Armstrong designs as so many other comp pedals are. It is chiefly intended as a sustainer, with the goal of long clean sustain with low noise. It achieves this by using an infinity:1 ratio and a low (but adjustable) threshold, which means you have to consciously use those qualities in order to get good results, whether for sustain or for any other type of compression.
The sustain is not "infinite" as the ads claim unless you choose a ridiculously low threshold. The high ratio makes it an excellent peak limiter, it really clamps down solidly no matter how hard you hit it. However the envelope of the effect (shape of the volume dip/swell) will not suit most slappers. The fixed attack is very fast, and the overall envelope is unusual: upon crossing the threshold your signal is dipped below unity gain, and then about half a second later it rises back up above unity and stays there. So the initial part of your note can sound extra rubbery and squashed, followed by an extended swell of sustain. This effect is more exaggerated the higher you set the sustain knob (which means the lower the threshold). If you set the threshold so that only your stronger peaks trigger it, then the rubbery attack is minimized somewhat. Also there is a blend knob, which is a bit confusing because Pigtronix says it is actually a ratio control. Do they mean ratio of compression, or ratio of compressed and uncompressed signals? It's actually a similar result either way, because the lower you set the blend knob, the more that your bigger signal peaks can get through.
The range of the sustain knob is essentially from "strong" to "ultra extreme"; in other words I was only able to get non-squashy sounding results by setting the sustain knob low, and using a bass with moderately low output levels. Using a bass with very high output, I found that it got quite squashy even with the sustain knob set all the way minimum. Aside from this envelope effect, the sound quality is very transparent, with no notable tone changes and no loss of highs or lows. There is very little inherent noise, however any comp that acts as extremely as this one will raise the levels of any background noise on your instrument line, and this one can do that to a glaring degree if you choose higher settings. At lower sustain settings it is quite tolerable.
There is a "grit" knob, which introduces a layer of distortion onto the effect. This is a somewhat fizzy hard-clipped dirt, not as smooth as their Disnortion overdrive but not a harsh "metal" distortion. At minimum settings it sounds pretty decent; turning it up higher does not sound so great to me, and loses lows badly for the first half-second of each note. Also I found the best results with the blend knob set at 100% wet, because otherwise the lows really sounded gutted and weak; although this can be mostly fixed by just turning up the output volume more. Again though, at a low setting with no blend, the OD flavor is entirely usable without having to crank up the output. There is also a treble-cut knob, which operates on a fairly high frequency range, and I didn't find it all that helpful. But if you are also using a dirt pedal that has too much harsh high end buzz, then the treble cut on the Philosopher could be useful to you.
The pedal runs on 12-20 VDC, and comes with a 15 VDC wall wart adapter. Many people don't like pedals that require special power supplies, but in the case of a compressor, extra voltage and/or amperage can really noticeably improve the headroom and reduce noise. However I was able to run the pedal successfully off a 12V/100mA outlet with no significant drop in performance. The construction overall seems rugged enough, and the footswitch is true bypass. This pedal was clearly designed with guitarists in mind; I wish they would produce a more bass-friendly version with an attack control and a much wider range of threshold, and maybe a different "grit" voicing. But even as it is, it's an excellent-sounding and very effective compressor, as long as you can live with the slightly weird envelope of the effect. It's also very small, which is remarkable with all the controls provided.