There are a number of factors that affect the recorded sound of guitars. Let’s start at the very beginning; the instrument itself. In the introduction, we discussed the various types of pickups and three basic guitar sounds, but there are other factors inherent in the guitar that determine how it will sound when recorded.
Setup: Of primary concern before we record a note of music, is how well the guitar is set up. This includes issues such as string height and pickup height. If not adjusted properly, improper string and pickup height will cause uneven volumes on different strings and different notes. Also, if the bridge is not properly set up, a guitar can have intonation problems. This will result in notes being out of tune in relation to one another as you go up the neck of the guitar. If a guitarist shows up to a session with one of these problems, there are solutions that will yield good results. If he shows up with all of these problems, cancel the session. On the other hand, recording a guitarist with a properly set up instrument will make your job that much easier.
Another issue to contend with is the wide dynamic range of the electric guitar due to guitar amplifiers and the various effects “stomp boxes” that are often used. Between uneven string levels and a wide dynamic range, we need a device that will even everything out and allow the parts to sit properly in the mix, and that’s where compressors come in.
A compressor evens out the sound of the guitar and brings it forward in the mix. (Another description of that effect is “the smooth and in-your-face sound”) By narrowing the dynamic range of the guitar and raising its overall average level, rhythm and lead tracks will sound more consistent with one another.
Considering the number of stomp-box compressors designed specifically for guitar that are available, you probably won’t have to compress at all. (Of course, their are always exceptions.) Since most guitarists spend a great deal of time developing their sound, all an engineer need do is record the sound accurately rather than being concerned with shaping the sound. You can add compression to the signal that’s coming into the mixer is you need to, but more than likely, if the guitarist has a compressor in his rig, you won’t have to. For a final mix, you may choose to, but that’s a topic for a later discussion.
In a multi-effect setup, and this applies to a rig with a number of effects units, the compressor should come first in the signal chain. This sounds best and will guard against strong input signals that might overdrive the inputs of the other effects processors.
Well-handled compression will add sustain to a guitar, which tends to make guitar players happy, and can also make each note more audible, which tends to make engineers happy as well. Be careful not use too much compression or the guitar will become lifeless. You can hear when a guitar is over-compressed by the fact that the attack of the pick will be exaggerated in comparison to the sustain of the note. For most musical applications, stay with compression ratios between 4:1 and 8:1, but feel free to experiment. You may find that a higher or lower compression ratio suits the sound you wish to create, especially if you experiment with different attack and release times. Also, a gain reduction of about 10dB seems to be effective in rock music. Another problem with over-compression is that you get a pumping or breathing effect, usually due to a short release time. Pumping can sound terrible, or can contribute to musical drive, particularly when timed to the music and used with percussive sounds. (See Live Sound Month, Processors-Compression)