A Uni-Vibe is a modulation effect that is often labelled as a Chorus/Vibrato but is in fact a phaser. The difference lies in how it's done: the uni-vibe uses a series of staggered filters that are phased, rather than aligned filters like you'd find on a standard phaser. Uni-vibes also do not use op-amp circuits for their sound. The result is that incredible swampy, pulsating effect that you hear on songs such as Jimi Hendrix's 'Machine Gun'.

Should my modulation pedals go before or after my distortion on my pedal board?

Popular consensus would dictate 'after', since the distortion will be flanged, (rather than a flanger being distorted, if you see what we mean) and will therefore sound more obvious and dramatic. If you are using a flanger, this is how you'll achieve those 'jet engine' noises. Not every one does this, though: one very influential moulation user, Eddie Van Halen, had neither a distortion pedal nor an effects loop and so he simply put all of his MXR pedals into the front end of his end and turned everything up. He changed history with his guitar sound so who are we to argue?

How many modulation effects can I use at once?

You can use literally as many as you can get your hands on! Blending modulations and stacking them up can be interesting and rewarding but there does come a point where, without sounding too facetious about it, four flangers doesn't really sound that different than three. With modulation effects, less is very often more, especially if big sonic gestures are being made. Don't let us stop you though: experimentation is what it's all about!

What is the best setting for the single knob on the MXR Phase 90?

Whether you want that awesome 'Eruption' sound or the haunting Pink Floyd 'Shine On' tone, your Phase 90's rate control should be set between nine and ten o'clock. Perfection lies therein.

Did Andy Summers use a Chorus or a Flanger with the Police?

Andy Summers' famously effected sound is responsible for lots of guitarists buying up chorus pedals left, right and centre in a quest to nail that tone. It's a shame for them all because that is most definitely a flanger on Summers' pedalboard. Namely, an Electro Harmonix Electric Mistress. Unlike the Deluxe model which had both Flanger and Chorus settings, Andy's regular Electric Mistress was a Flanger only. Medium settings on most vintage-styled flangers will get you close and, as ever, listen with your ears and not your eyes!