Do they make pedals that can do this?

[Tupac]

Drop the pitch of all notes to whatever amount of half steps you want? It's be like drop tuning... without the tuning.

[natw42]

Morpheus Drop Tune... any users?

Morpheus Drop Tune pedal - according to the thread I linked, it doesn't work well on low freqs.

Never used it myself.

[Crystalman85]

Actually there is...a whammy pedal can do that.

[alec]

There's the Morpheus Droptune http://morpheusefx.com/droptune.php and plenty of others. Eventide for example.
A lot of multi fx do that sort of thing.

[cybersnyder]

I tried the Morpheus and didn't like the results. Played around with some pitch shifting on my M5 and was more pleased with the results. There will be some synthetic texture to the sounds so I feed it into my EVH Phaser in script mode with the knob turned all the way down. That, for some reason, tames the pitch shift synthetic sound. Still not perfect, but it'll work.

[sillyfabe]

I use the Boss PS-3 Digital Pitch Shifter/Delay for this. Its a D/C'd model but can be found from time to time in the classifeds. VERY versatile pedal but it can do polyphoic tuning with semitones avaliable from -1OCT all the way to +1. It can also do -2 and +2 OCT. I use this in mode 10: which blends 2 different pitch shifts with your clean (or you can dial out your clean) for some cool sounding harmonies.

I either use:
clean/-4th/+5th
no clean/ -3rd/+3rd
and a few more...

[G3Mitch]

whammy DT sounds like exactly what u need??

[ACalbass]

Tupac
You have to keep this in mind :
All effects that will do this work taking the incoming sound,which is analog,converting it to digital,then manipulate it produce the effect,then converting it into analog again to output to the amp.
In all this process,there is big amount of quality involved that is lost.
If you plan to run ONLY the effect's output,as to listen the detuned notes alone,you must know that you will get a sample of your actual sound,not the sound per se.
This sample sound might not be perfect and can have a lot of artifacts,depending on the quality of the the A/D and D/A converters,plus the sample quality.
As most people run the effects in the background,meaning a MIX between the clean sound and the effect,this artifacts don't make a significant problem,but I can see that will be significant in the way you propose to use it.
I am writing this after testing some effects only output from my rackmount fx processor,actually a digital delay that can detune by semitones the output.
It is possible to do what you say,but is clear the output is not keeping the original sound quality.