Last time we discussed double-tracking problems you can avoid by doing Guitar 1 well, so this time we'll cover the same for Guitar 2.
Aside from the difficulties mentioned under "Performance Issues" below, there are some disadvantages to double-tracking:
Let's tackle these one by one. It's true that individual character can be overshadowed, but this will depend largely on your style. More improvisational players are more affected, but some find it easy to play something repeatedly. It's a judgment call only you can make. In exchange for some individuality, you get a thicker, fuller sound. One or the other will be worth its weight in gold to you.
If you record in your own studio, the extra time for double-tracking won't cost more money, but in either case, consider this: if it takes you 20 minutes to record Guitar 1, it will not take you another 20 minutes to record Guitar 2. In my experience, it takes a quarter of the time for Guitar 2 (5 minutes). This happens because your playing is already smoking by the time Guitar 1 is done. If you're not improvising, you've also been playing the same line for 20 minutes.
As for guitarists assuming you couldn't double track something, not every guitarist has this competitive attitude. Many are just good musicians who, like you (hopefully), care more about the song than their ego.
If you're a metal head, the traditional mixing approach is riffs hard-panned right and left, lead guitar straight up the middle, but the whole point of double-tracking is to have full stereo leads, usually hard panned, too. Now you've buried your rhythm section!
If Guitars 1 and 2 play in unison and then break into harmony, or into two completely different lines (Guitar 1 is a slow melody while Guitar 2 is a fast scale), both guitars may sound quieter overall.
Both issues can be solved by double-tracking the original lead all the way (Guitars 1 and 2), then make the harmony/dual part into Guitar 3 (and maybe Guitar 4, if you double-track this, too). Be aware that you're more likely to bury the riffs this way. A lesser solution is to raise the volume where needed, though this doesn't always work.
In the previous column, I mentioned using two different articulations for Guitars 1 and 2, in which case the performance will not be exact by definition. If you use the pick throughout Guitar 1 but use slurs within Guitar 2, for example, you may have to experiment with exactly what is different (and when) to make this sound good with full stereo separation. Sometimes there's no choice but to put both guitars in the middle of the mix instead.
This is the most obvious issue with double tracking and is why most people don't do it.
Practice. Guitarists practice all sorts of things with a metronome, but you need to practice double tracking itself. There is nothing like playing along with yourself to discover how inaccurate your timing is. You need to learn your own habits to fix them.
Whether ear fatigue, the cord getting in the way of your windmills, or just a fashion emergency, headphones can drive people crazy when recording, so how do you double-track without them?
Sometimes the guitar just goes out and you can't get it back in tune with Guitar 1. Now what?
Sometimes you let go off the last note at different times for each guitar, or one has better sustain. We're not talking huge differences here, but even small ones can sound bad, especially if there's a rest in the whole band right then or your digital delay repeats the two slightly-off endings over and over!
If you decide to double-track certain lead phrases and not others, it is good to know this in advance. After all, let's say you decided to double something, did so, and change your mind later? Simple. You just turn off one guitar. But what if you didn't double it and now wished you had? Can you get the gear set up (if it's gone) and re-perform it days or weeks later? My solution is simply to double everything and make my decisions during mixing, but I own my studio and am a glutton for punishment.
So is double-tracking worth it? Here's a final thought. It often sounds good to double your themes, which tend to be simple and easier, and not double your more solo-like passages. You keep spontaneity where you need it and get fuller sounding themes. It's the best of both worlds.
Best of luck, and may your fingers fly true... both times.
Randy Ellefson is an instrumental guitarist with endorsements from Alvarez Guitars, Peavey, and Morley Pedals, and a Bachelors of Music in classical guitar, Magna Cum Laude.
His most recent album, "Some Things Are Better Left Unsaid", was independently released in July 2007. Ellefson is also known for his extensive experience with tendonitis, which once took away his playing for five years.