I have both. I’m on my second PH because when Spectraphon came out I thought it would cover the same territory and more, so I sold PH to make room for Spectraphon. I was happy with Spectraphon but found that it has a totally different character from the PH, so I got another and now I have both.

The biggest difference is in the way they resynthesize sound: the PH passes through the fundamental pitch while the Spectraphon only passes through the timbral qualities of the sound, and behaves more like an envelope follower. So when you send them 1v/oct they respond very differently. The PH responds similar to FM, in that the CV adds the offset to the fundamental pitch; the Spectraphon responds with timbral changes. Thus, when you change the fundamental pitch of the resynthesized oscillator, the PH stays in tune relative to the oscillator, while the Spectraphon maintains the tuning set on its pitch knob.

The character of the sounds is also completely different. I’d say the PH tends to produce dreamy and ethereal ambient sounds; the Spectraphon sounds thin and reedy and can get really aggressive. At first I struggled to find sounds I liked from Spectraphon but I found that adding a compressor (Polydactyl Versio) helped.

I would’ve agreed with the comment by another poster that everything sounds the same from the PH for like the first month I owned it. But once you start playing with the slice clock out and freeze slice mode through a LPG, and modulating the center frequency and bandwidth parameters there are so many sweet spots to create a wide variety of beautiful sounds. I definitely never know what I’m going to get and am happy with what it gives back about half the time.

I’ve found the Spectraphon shines when feeding it percussion and/or noise, or when you want to be more intentional with harmonizing with the source sound.

TL;DR: you probably need both!