What is a rotary speaker?
A real rotary speaker is a device constructed by Don Leslie as a way to get a Hammond Organ to replicate the spread sound of a pipe organ. It´s designed to get the sound inside the speaker cabinet directed by rotating objects, using amplitude and frequency modulation and the doppler effect. The result is a complex mix of tremolo, phasing, pitch-hifting and ambience which gives your tone a rather unique flavour. These original speakers are really big so an emulating pedal is way neater (and it doesn´t kill your back on your way to the gig!) and a really great invention.
Any good examples?
Beatles used the Leslie rotary speaker on many tracks and different instruments, the vocals in "Tomorrow Never Knows" is one example, the lead guitar in "While My Guitar Gently Weeps" is another (played by Eric Clapton, who has used this effect on many tracks, originally inspired by The Beatles great use of it). You can also hear the characteristic effect on the Tom Petty song "You Don´t Know How It Feels" and on Soundgarden´s "Black Hole Sun". Another guitarist that liked this effect was Jimi Hendrix, who employs it on the solo of "Little Wing". David Gilmour of Pink Floyd uses the rotary speaker effect on tracks like "Brain Damage" and "Any Colour You Like". A more modern example is Alex Turner of the Arctic Monkeys who uses the effect on tracks like "The Hellcat Spangled Shalalala" and on the solo on "Teddy Picker".
Which pedal should i get?
There´s two really great options, the Hughes & Kettner Rotosphere and the Strymon Lex. The Rotosphere may be a bit noisy, but that´s what a real Leslie speaker is as well. The Lex is a bit more quiet unit that´s also half the size of the Rotosphere pedal. But if you choose between these two pedals, let your ears be the judge instead of the size. Which one that sounds more authentic is for you to decide. Dunlop also makes a rotary speaker pedal in a somewhat different shape; their Rotovibe has been made in the wah-fashion with a switch that can be rocked forwards and backwards to change the frequencies. Another fan of rotary speaker emulation, Zakk Wylde, has his own signature serie of this pedal.
What is a phaser?
A phaser effect is produced when the guitar signal is split in two signals, one of them is altered by a filter which creates peaks and notches in the phasing spectrum. This signal is mixed together with the original signal, which results in two signals that are out of phase with each other and the notches that occurs gives the characteristic phase effect. A flanger is a similar effect, the difference is that a flanger delays the altered signal where the phaser does not.
Any good examples?
There are many different examples, for instance the phaser played a big part in Eddie Van Halen´s "brown sound", which ca be heard on tracks like "Atomic Punk" and "Eruption". A very different guitarist that uses the phaser in many songs is Radiohead´s Johnny Greenwood, listen for example to "Paranoid Android" for it. Classic Rock guitarists Brian May of Queen and Jimmy Page of Led Zeppelin likes to emulate their sound with a phaser, listen to "We WIll Rock You" and "Ten Years Gone" for good examples. A modern alternativa band that likes to use a phaser is Tame Impala, you can hear it on tracks like "Solitude Is Bliss". Nu-metal act P.O.D. and alternative rockers Incubus are also fond of the phaser effect and uses it everywhere, Incubus even has a song fittingly named "Just A Phase".
Which pedal should I get?
To begin with the classics, the EHX Small Stone is a great pedal, so is the MXR Phase-90. The first one is used by Johnny Greenwood and Korn guitarist Munky, the latter has fans like Tom Morello (Rage Against The Machine, Audioslave), Dave Grohl (Foo Fighters) and John Frusciante (Red Hot Chili Peppers). But there are other choices too, like the versatile Boss PH-3, the Digitech Hardwire SP-7, the T-Rex Tonebug Phaser or the Epress Effects Phaser Pedal. From one knob to five, the choice is yours. Remember that sometimes simplicity is best, but not always, it all comes down to your taste.
What is a flanger?
A flanger effect is produced when the sound from your guitar is mixed with a copy of your signal that is delayed by a small and gradually changing period. When this signal is mixed with the original signal the frequency spectrum is changed in peaks and notches which produces a sweeping sound. The two signals kind of moves around and relates to each other in a linear harmonic serie. The flanger sound can often be described as a "jet plane" or a "swoosh".
Any good examples?
An early example of flanging can be heard on the rocket launch sound effect on The Ventures version of the song "Telstar". John Lennon became a fan of flanging when he got tired of double-tracking his vocals and engineer Ken Townsend solved the matter by inventing something he called Artificial Double Tracking, which was a kind of flanger. Lennon loved the sound and tried it on many tracks, the first one in the Beatles catalog is "Tomorrow Never Knows". Eddie Kramer did the fisrt stereo flanging on the coda, the fantastic outro solo, on the Jimi Hendrix song "Bold As Love". Jimi stated that this was the sound he hd heard in his dreams. Another famous user of flanging is Eddie Van Halen which can be heard on several Van Halen tracks, a good example is "...And THe Cradle Will Rock". Other examples of a flanger can be heard on songs like "Animal Nitrate" by Suede and the breakdown section before the solo in the Lenny Kravitz song "Are You Gonna Go My Way".
Which pedal should I get?
The two Boss pedals BF-2 and BF-3 are classics, but although their names are similar there´s many differences betwen these two pedals. To use an easy explanation the BF-2 sounds analog while the BF-3 is a digital unit. For the Van Halen-fan there´s an easy choice - the MXR EVH117. Another guitar hero with his own signature flaner is Paul Gilbert with his Ibanez AF-2 Airplane Flanger. Electro Harmonix has their own flagship in the Electri Mistress Flanger, famously used by David Gilmour on Pink Floyd´s classic album "The Wall". And ther´s of course more options out there, so go on and try a few before you make your decision. It´s your ears that decides which flanger that suits you best.