Getting started on this blog has been a bit of a challenge. There's a lot to say, tons of gear to review, ideas and suggestions, common questions, all sorts of stuff. To start off, though, I'll just jump right in with a technique that I use often, and one that I don't hear people reference as often as I would expect.
"Multing" is the practice of splitting a signal, so that you have the same feed going into parallel circuits. For instance, you might send a vocal to both a light compression with some reverb, and to a parallel circuit with very heavy compression and eq. When the two signals are recombined, you get a vocal that has the nuance of an unprocessed track, but with the presence and shimmer of one that has been 'cooked'.
To do this in the analogue realm, you can use a simple "Y" cable, or you can use a half inserted "insert" cable. In the case of the "Y", simply plug the cable from your tape machine into the "y", then plug into the line-in on two channels of your board. To use the Insert, simply use a patch cable halfway inserted, so that it taps the signal without interrupting it, then plug that into the line-in on another channel.
In the digital world, simply copy the track you want to mult, and paste into a new track, making sure that the start points are the same. In Cubase, for instance, you can option drag while holding down the command key (on Mac), to make a copy that is perfectly aligned with the original.
You have to be a little carefule about phase issues, as some processors or plug-ins introduce a small amount of delay, which can be problematic. I usually insert the same plug-ins on both copies, and leave one turned off, to correct for any latency issues.
So, now that you understand the basics, where can this be helpful?
Generally, anytime that you wish you had more signal to work with, a mult can be helpful. Say, for instance, that you have a great bass tone, but you'd like it to have some fuzz in the upper registers. You try putting a distortion or overdrive plug in, but now the low end sounds wooly and lacks punch. This is a good place to use a mult. Keep one channel sounding nice and tight, but run the other through a fuzz patch, then cut everything below about 2khz. Now you have a bass that has an articulate high end with some edge, and a low end that still punches and feels tight.
Similarly, you may find that a kick drum isn't punching through the way you want it to. In this case, you might mutl the kick, compressing one channel hard, with a bit of boost in the lowe frequncies. This will give you nice boom and sustain, but now the attack is pretty much gone. You can try slowng the attack of your compressor, but the results may not be what you're looking for. In this case, you can use the second track to get a nice crack around 5k, and a good punch at 1k. I like to use a gate on my "attack" track, so that it only opens for a few milliseconds. Then, after the gate, I run it through a distortion patch. This give a very bright attack, but without adding a bunch of noise to the whole track.
You can use the same approach on a snare. Sometime, I get too much bleed from the high-hat on my snare track. If I boost the highs to get a good clear attack, I get a ton of hat. If I try to gate it, it sounds too mechanical, and fake. The solution? The Mult, of course! Set up one track with some eq cut in the highs, a bit of compression, and some boost in the 200hz range. Now, take the second channel, and set up a tight gate. Let it stay open for maybe 50 milliseconds, so that fast rolls can keep the gate open. Now, eq this channel for the high attack you want. You can even limit it, or distort it. Whenever the drummer hits his snare, this cracking track will be audible just for an instant, while the first snare track rings out naturally.
I use mults all the time, and it's a useful technique for solving problems, creating larger than life sounds, and getting mixes that can compete with the big boys.