Electric Guitar
Compared to the acoustic guitar, there are many more variables involved in achieving the desired sound from recording. Most of these lie with the guitarist and his/her equipment. Guitars, amplifiers, cabinets and effects all add to their tone and usually the sound they have created has been perfected over many years. In come cases this is not so in which case the engineer has to intervene more.
The electric guitar works in the following way. The guitar is played and the vibrations are detected by the pickups in the body. Simply put, these are magnets which turn the motion of the string into electrical energy. The signal is then fed into the amplifier where extra tone and volume along with any other effects are added. This is sent along another cable into the speaker cabinet which is usually a 10" or 12" speaker. There are so many different types of guitar equipment but they all work using the same principles. By understanding the way in which it works, it makes it easier to work out signal flow so different guitar recording techniques can be employed.
The speaker cones within the cabinet are never short of power usually so getting a healthy signal level from a microphone is never a problem. As loud as amps are, the tone they deliver are never that pure because they are often noisy when distortion and effects are added. Because of this and the way that the speakers are designed, their high frequency response tends to be quite limited which means that usually only cardioids dynamic microphones are used. It is worth experimenting with condenser mic in some situations as they tend to give more of an 'American style' tone from the same guitar output. Again, the choice of microphone is dependant upon the sound that is required from the recording. With some guitar tones, they might sound quite piercing at the high end in which case using a mic with a presence peak is not advised as this will only exaggerate this. It can be used on amplifiers which may struggle with produced any high end and are very 'muddy' in sound tonality.
The constant war between most guitarists is the decision on whether valves sound better than solid state amplifiers. Both have their merits but this is down to personal preference and merit. Whichever one is to be recorded, different approaches to record them are needed. Valve amplifiers work their best with lots of gain and lots of volume so if working in a studio where more than one guitarist is playing the same room at the same time, problems with overspill could occur. It is always best record guitars separately, if possible, to avoid any overspill issues. Valve amps also provide a lot of hiss to their sound which is especially noticeable at low playing levels. This hiss is in the presence band and can be removed by eq usually but careful positioning of the mic to the cabinet can reduce this. Solid state amplifiers will produce the same sound at low levels and high levels so they can usually be recorded with ease if other people are playing in the room at the same time. However, depending on how good the amp is, most solid state amps tend to have a poor high frequency tone. This is usually noticeable when no matter what position the mic is in, the recorded sound still sounds very piercing and lacking bass end. A good balance between position of the mic and sound output level is required in this circumstance.
When recording cabinets, there is one key factor which governs the way the output is picked up by the microphone. The more on-axis and central the mic is to the middle of the cone, the brighter the tone. So as mentioned before, to achieve a well balanced sound from a naturally bright cabinet, you would position the mic away from the cone.
The number of mics to be used in the recording can be decided in a number of ways. If the cabinet is open backed, two microphones can be set up around it. Open backed cabinet produce around the same output from the front of the cone and the rear but the sounds differ slightly. It is sometimes worth positioning one mic round the back, also off axis. As you would then be recording the same output but from two separate sources in the room, it is worth altering the phase input on the desk if possible to see which sounds better.
On cabinets which have more than one speaker, i.e., a 2x12 and 4x12 more than one microphone can be used. However, as the impendence is split evenly among the speakers so technically there would be no difference in what you record. Excluding modified cabinets, some guitarists might say that the sound is different per speaker but this is only true to a certain extent. The effect is more noticeable with slanted cabs (where the top two speakers are slightly angled) as more of the sound is being projected towards the ears. The remaining two speakers are still projecting along the ground level so that seems bassier. In this situation a good way of setting up the mics is to have one pointing at the speakers as normal, then another about 12 foot away in front. Phasing issues will be less of a problem in this instance because the direction of the cone is always the same for when the sound hits both microphones. It is still worth experimenting with phase if possible. This however depends on the acoustics of the room sounding nice to begin with but in this case it is more forgiving as the guitar is such a big sound.
If the guitar player has several effects to be used in one song, it is important to note that the volume drop can often be quite great, especially when using stomp boxes. The best way to record these different sounds is by doing individual takes of them all (if the guitarist will permit!). All the sounds can then have individual eq and compression added later on as every sound is very different. The end result will be a much smoother and consistent transition in between sounds. This also means that it leaves the option open of letting notes fade out naturally as the lengths can all be adjusted post recording.
If the sound is too 'dry' and more of the actual guitar sound is needed, rather than the amplifier, using a condenser mic will help. As mentioned before, the guitar amplifiers frequency output is limited but the sound of the actual instrument isnt. The electric guitar is still very similar to the acoustic guitar even though the one is hollow bodied and the other is not. When the strings are played, sound still resonates out from the body of the guitar too. Miking up the strings as they are played will add a more natural sound to the overall output. This will add a lot more definition to the notes as they are played. For this method to work, the guitarist must be playing in a separate room to the microphone otherwise too much overspill into the condenser will occur. Setting the guitarist up in another room anyway is never a bad idea unless he/she needs to use the feedback and the sound from the amp to play.
A more modern and very effective way of recording electric guitar now is using the method of re-miking. This is useful in situations where the guitarist has lots of sounds or wants to use lots of sounds that he/she does not have. This is also useful to the engineer is not not happy with the tone but needs to record anyway due to time constraints and other pressures. This method can be done in a two ways. The first is to plug the guitar into the desk or preamp which then feeds through to a live room where a stack or combo amp is set up. The signal is then miked up and played back through the speakers for the guitarist to hear. The dry signal which feeds the amp is then recorded which can be later be fed into another amp or into emulating software on a different day. The second way is to do plug the guitar in to the desk or preamp then plug this straight into a software emulator and still record the dry signal. This way, no amp is even needed for recording and depending on the outcome, might never be used.
When recording guitar in a control room, the only other thing to look out for is interference from studio equipment. CRT monitors will produce the most interference which is picked up by the guitar's pickups. Active humbucking pickups (powered by a 9v battery) are affected least by interference. To avoid this, when recording turn off the monitors. The studio must be properly grounded in order for any unwanted frequencies to appear on the recordings. Metal computer cases or rack gear that is not earthed properly can transmit a mains hum along the signal wires.
Bass guitars behave in the same way to electric guitars in terms of acoustics. As their tone and pitch is much deeper, dynamic microphones sometimes struggle to pick up the acoustics well. Bass cabinets normally use 10" speakers but the same miking techniques for electric guitar still apply. Using a large diaphragm microphone will help pick up the very low end in order to achieve a better recording. The same type of methods of recording also applies i.e., re-miking.