A whammy bar or tremolo arm is a popular tool used in guitars that opens up a whole world of tonal possibilities, the basic mechanics of this is the when the bar is pushed down (into the strings), the strings get loosened and this effectively de-tunes them and makes them go down in pitch creating cool effects that can supplement your riffs.
The way I use my whammy bar is as an extension to my bends, you should approach the use of the whammy bar as you would to normal string bending using your left hand, by this I mean using it sparingly, to add dashes of colour, some guitarists like to go crazy with it which is great but I believe it should just supplement your guitar playing rather than being the key feature. The way I like to prepare for using my whammy bar is having it under my palm ready to be used in a split second, this way is more convenient than grabbing it when you need it but can be restricting when you're not using it, the choice is all personal preference and you need to find what works for you. It's also important not to accidentally touch the whammy bar when you're playing unless you're using it fully, as this will effect the pitch of your strings and make it sound out of tune.
Whammy Tricks (Video Below)
The most common whammy trick is to use it to create vibrato, vibrato is usually done manually by bending the string up and down swiftly, but not bending the string too far, this creates an effect that sounds very vocal, because that's how singers sing their notes, by slightly quivering the note, so to create vibrato with your whammy bar just play your note and wiggle the bar up and down fairly fast.
If you take a look at riff 1 in the video above you'll see the downward bend whammy trick, you've just got to push the whammy bar a bit deeper and faster than you would for the vibrato and only push it once per note, after you've bent your string down using the whammy bar you have to play the next note without bending up slightly before when you release the whammy bar, this is a difficult trick to get right but if you do it will really make the guitar sing.
One of the most common and cool sounding tricks is the dive bomb, used heavily in metal by guitarists like Zakk Wylde and Eddie Van Halen, the trick is to play natural harmonics (usually a mix of two strings- fret 3, 5, 7, 12) once you've hit that note or collection of notes, pull down your whammy bar and it'll sound transformers level crazy.
A similar trick is the elephant trick, created by Eddie Van Halen, with an amp channel with lots of gain you need to start with your guitars volume turned all the way down using the tone pots - or a volume pedal if you have one, then play:
The 3rd string on fret 5
The 2nd string on fret 7
The 1st string on fret 12
Once you've played those notes together clearly with the volume still down on your guitar you need to press your whammy down a bit (not too much) and then bring up your volume on the guitar while bringing up your whammy bar and as long as the notes are still restating you should get a super cool sound of an elephant squeal.
Steve Vai's Trick
The last trick I like to use is a trick that used a lot by guitarist Steve Vai, if you take a look at riff 2 in the video above you'll hear a variation of it, the basics of it are to give the whammy bar a fairly quick pull on every note you play, while going up or down a scale/arpeggio or any lead line, so you play a note and then play the same note as a whammy, this make it sound like you're playing the same note twice with a dip in between them and sounds incredibly melodic. The trick to this one is to keep the whammy bar close to you so that you can use it after every note without having too much of a break in-between, just look at how I'm holding it in the video.
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