Photo: Richard Ecclestone
This article effectively covers two areas — the basic methods of recording the electric guitar and some techniques for recording and processing that are specific to Logic. So, if you're not a Logic user, the majority of this article will still be useful to you, and most of the Logic part can be applied to other software platforms. At one time the only accepted way to record the electric guitar was to mic the amplifier, but now there are guitar recording preamps (both analogue and digital), active and passive speaker simulators, and software modelled guitar preamp plug-ins to choose from. There's also the option of buying a speaker cabinet in a soundproof enclosure, which you can connect to your own amplifier and then mic up conventionally (the mic goes inside the box with the speaker, just in case you were wondering!) without allowing more than a whisper of sound to leak out into the room. Which option you choose depends both on your recording situation and on the sound you wish to achieve. Most players agree that a nice amplifier, properly miked, still gives the best results for traditional electric guitar sounds, but some of the digital emulations now get very close indeed. Interestingly, we tried all these options recently during a seminar that we put on for the London Guitar Show and the results were most enlightening.
If you are going to mike up an amplifier, it obviously needs to be a nice-sounding amp, and for most discerning players that means a well-maintained tube amplifier of some kind. Unless you have a very large recording space, a smaller amplifier is easier to mike up than a large one and the 6W Cornford amp that Dave Lockwood played through at the guitar show proved to be so loud that we still needed to use a power soak with it to cut down the level reaching the speakers. If you have a larger amplifier than this, and most people have, then a power soak between the amp and speaker is a good way to keep the level down while still allowing your amplifier to work hard.
While it's easy to suggest mic types for vocals or specific acoustic instruments, you can try just about anything you have on a guitar amplifier and get an interesting tonality. The old standby is a Shure SM57 or Sennheiser MD421 dynamic cardioid, but you can try literally any dynamic or capacitor mic you have in your locker, from the cheapest to the most esoteric. Often where you place the mic makes more difference than what the mic is, and sometimes a mic that sounds dreadful on vocals can sound very musical on guitar.
You'll notice that the sound becomes more focused as you move the mic closer to the speakers, and it also gets more mellow as you move away from the centre of the speaker towards the edge of the cone. You can also turn cardioid mics slightly so the sound is hitting the mic off axis if you need less top end. In most studio situations, cardioid mics are used to reduce the amount of spill or room interaction, but as guitar amps are relatively loud and the mics generally set up pretty close, you can also try omnis or figure-of-eights if you have them and the spill shouldn't get much worse.
Although the traditional rock approach is to put a dynamic mic right up against the grille, you can often get a better sound by backing off from the speaker slightly, just by a few centimetres. I've also had good results miking the back of an open-backed cabinet or, in a decent-sounding room, putting the mic up to a metre away from the front grille. In this latter case, placing a reflective board on the floor between the amp and mic can liven up the sound in a very useful way. You'll also find that the sound changes depending on whether the amp is on the floor or on a stand (or chair), as the floor reflections will interact in a different way. Open-backed cabinets tend to have a 'bigger' sound than closed ones, as the speaker doesn't have a cushion of air to damp it, so low-frequency sounds seem more pronounced. Where you have the facilities, you could also try combining the outputs from two mics, one close, and the other further away, or one in front of the amplifier and one behind.
Of course, using two mics on any source raises the issue of phase. If your mixer has a phase switch, listen to see what difference reversing the phase of the distant mic makes, as this will affect the way the sounds combine — you can also vary the mic distance to adjust the relative phase of the two mic signals. If you want to be purist about it, you can use Logic's Sample Delay plug-in to delay the close mic so that it is in phase with the distant mic. Sound travels at roughly one metre every three milliseconds, so to add three milliseconds of delay at a 44.1kHz sampling frequency you'd need to add a delay of about 132 samples. You can fine-tune the result by ear to see what value gives the most solid sound.
Where the sound of a cranked guitar amplifier would cause problems with spill (or neighbours!), a good combined power soak and speaker simulator will allow you to DI your guitar amp without the speaker connected and still capture something very close to its natural tone. However the results vary drastically from model to model.
A typical speaker simulator comprises a reactive dummy load, allowing the amplifier to work normally, followed by circuitry that approximates the filtering effect of a guitar loudspeaker. Apart from the dummy load, which is, of necessity, passive, the filter circuitry that replicates the speaker's frequency response may either be passive or active. The output appears as either a mic- or a line-level signal, which can be plugged directly into a mixing console. Most power soaks can handle between 50W and 100W of input power, which means that the majority of guitar amps can be run flat out to get the best overdrive sound.
Isolation cabs can work exceptionally well and also allow you to experiment with different microphones, though the tonality of the speaker in the cabinet may not exactly match the one in your amplifier. Nevertheless, this is a very practical way to work where you wish to retain the essential character of your amplifier, even though a little EQ may be needed to get closer to the sound of your own speakers. Using power soaks or speakers inside isolation cabinets falls somewhere between true amp miking and the 'short cut' world of digital amp emulations.
Although there are still some excellent analogue recording preamps made for guitar, digital models are currently the most popular and arguably the most versatile. Both are used in essentially the same way, by DI'ing their outputs at line level, though with an analogue model you'll probably have to add your own delay, chorus, and reverb effects afterwards if you need them.
Some of the digital emulations are incredibly good, and very versatile tonally. If anything, they miss out on capturing the real low-end thump of a close-miked tube amplifier, but they can get pretty close to the sound of a range of real amplifiers, and the better ones also respond well to playing dynamics, such as picking intensity or backing off the guitar's volume control. Logic Pro now includes a very simple but useful guitar preamp plug-in, and an even simpler version (lifted from Garage Band) is included with Logic Express.
The only technicality to consider when recording a guitar for processing via a software plug-in is that guitars need to be fed into a high-impedance instrument input, not a mic or line input, so if your audio interface doesn't have one of these you'll need to buy an active DI box with a high-impedance input, and then connect this to the mic input of your audio interface (or the mic preamp connected to your audio interface). Most active DI boxes can be run from a phantom-powered mic input to save on batteries. You'll also need to set your system latency (buffer size) to its lowest stable value if the player is going to monitor the sound with Logic's effects and amp modelling added.
The only realistic way to evaluate a modelling guitar processor or plug-in is to listen to the sound over the studio monitors and see how it stacks up against the guitar sound you hear on records in a similar style. You can't expect to get the same listening experience sitting in front of studio monitors that you get standing in front of a 100W stack, because the volume level when you play back a record is very different to what the guitarist hears at a live gig. This may sound obvious, but it's surprising how many guitarists comment that the sound isn't as big or powerful as it is when they're actually playing.
Electric guitars don't have great signal-to-noise ratios, especially those fitted with single-coil pickups which are prone to receiving hum from surrounding wiring and equipment. In particular, CRT-type computer displays and TV monitors affect guitar pickups very badly, so a flat-screen computer display is strongly recommended. Logic doesn't have a specific de-humming plug-in, but by using two EQs in series you can set up a whole series of very narrow notch filters starting at the fundamental frequency of your mains supply. In the US this is 60Hz, but in Europe we like to do things a little more slowly, so we have a 50Hz supply. In Europe, the filters can be set for 50Hz, 100Hz, 150Hz, 200Hz, 250Hz, and so on. If the hum doesn't have too many buzzy harmonics, four or five filters should be enough. Because of the precision available with digital filtering, even quite severe buzzes can be removed with little subjective effect on the wanted part of the guitar sound. However, don't make the filter notches any deeper than you need to, as you may then hear too much tonal difference.
Broad-band noise can be removed with de-noising software, but sadly Logic's Denoiser plug-in is next to useless (aside from emulating live news reports from war zones!), which is odd when you think how good the other plug-ins are. If you have really serious noise problems, then the TC Powercore or Waves sound-restoration plug-ins will do a good job on steady background hiss, as will Bias Sound Soap and Sound Soap Pro.
Logic's Noise Gate or Expander may be used to clean up the pauses between notes or phrases, but as electric guitars can sustain for a long time, there may be few periods of true silence where the gate can be effective. In any event, the gate release time needs to be set long enough to allow the guitar to decay naturally without being cut short. Any such noise-removal processing should be applied before any delay or reverb effects are added. This way the reverb or delay will still decay naturally and help cover up any audible artefacts caused by the gate or filter action. Where you're using a lot of overdrive, cleaning up the sound with a gate or expander is a good idea.
Logic's High Cut EQ and Low Cut EQ can also be effective in cleaning up the sound of the electric guitar, because, as a rule, the guitar sound has quite a limited frequency response, while the noise may continue right to the extremes of the audio spectrum. By setting the upper cutoff frequency to between 2.5kHz and 4kHz, it is often possible to significantly improve the signal-to-noise ratio of a typical electric guitar sound without dulling it excessively — use a filter slope of between 12dB/octave and 24dB/octave. Rolling off all frequencies below 80Hz or so may also help clean up the low end.
Finally, some of the best clean electric guitar sounds are obtained simply by connecting the guitar to the computer's audio interface via a DI box — just add a little compression, gentle EQ, and perhaps a hint of reverb. This style of recording can suit funk music, though rumour has it that the guitar on Pink Floyd's 'Another Brick In The Wall' was also DI'd clean and then compressed.
Recording engineers tend to like leaving as much processing as possible to the mixing stage so as to keep their options open for as long as possible, whereas guitar players like to hear something approaching the final sound as they record — what they hear affects the way they play. For that reason, stomp-box effects are often recorded rather than added later, though effects such as delay or reverb might be safest left until mixdown. If the player needs to hear these to feel comfortable, they can be mocked up in Logic for monitoring using any of the available reverb or delay plug-ins. Ultimately, the performance is what really counts, so whatever keeps the player most happy tends to be best in the long run!
Some engineers have been known to re-amp a guitar track by feeding it out through a guitar amplifier, which is then miked up and re-recorded onto a spare track. This can sound very effective, but can also be a bit tedious to set up. However, if you have the facilities to do it, then give it a try. It's also a great way to take the nasty edge off a guitar track that has been recorded with some inadvertent clipping!
A lazy equivalent is to take a basic guitar track and then further process it through a modelling preamp plug-in such as Logic's Guitar Amp Pro, and I've done this very successfully with both guitar and bass-guitar parts. If only the tonality needs changing, you can pick a clean, benign amp model (or even bypass the amp model altogether) and then try out different speaker types, whereas if you want more overdrive you can add that by picking an amp model designed to produce overdriven tones. The electric guitar sound is not, and never was, natural, so there are no real rules as to how it should sound.
You can also use Logic's Channel EQ to shape the sound. Some of the frequency ranges described below may be of help:
Cut applied at between 120Hz and 280Hz can help reduce lower mid-range muddiness or boxiness. Boost in the same range can fatten a thin sound, often in combination with some upper mid-range cut.
Cabinet thump can be accentuated by boosting at around 75-90Hz, though how successful this is depends on what is present in the original signal. If all else fails, you can use a little of Logic's SubBass plug-in to bring in those deeper frequencies that may be missing from your recording. Just don't overdo it!
Bite or definition can be added to the sound anywhere between 2kHz and 4kHz. There's little point in boosting higher than this, as guitar speakers tend to roll off sharply above 4kHz, so there may not be anything left there to boost other than hiss.
A fizzy high end can be tamed by using a high-cut filter with a steep roll-off, adjusting the frequency as low as possible such that the essential bite of the sound isn't adversely affected. This will attenuate all frequencies above the filter cutoff point and produce a more focused sound as a result.
Aside from optimising the EQ, what else can you do to a guitar sound? The answer depends on whether you want to enhance the sound in some way or change it into something radically different. Logic offers tools for both as well as ones that fall somewhere between these two extremes. The obvious effects to explore for traditional guitar sounds are reverb, delay, chorus, phasing, flanging, vibrato, and so on, but I find simple compression very useful, on both clean and distorted electric guitar. You'll often find that using as much distortion on a recording as you do live results in a very messy sound that spreads right across the frequency spectrum, so a useful trick is to use less overdrive on the guitar and then add compression to get the sustain back.
Using a faster release time in combination with a high degree of compression can cause audible level pumping, but this may be used creatively to enhance the sense of power and loudness. Medium to high compression ratios (between 4:1 and 10:1) work well for this, with the threshold set to give between 8dB and 15dB of gain reduction on the loudest peaks. In Logic's Compressor, try the Peak and RMS side-chain settings and see which one suits the sound best. Of course you have to bear in mind that every decibel of compression you add reduces your signal-to-noise ratio by a decibel, so it is advisable to clean up the signal first using a gate or expander.
If you're after a conventional rock guitar sound, then the basic overdrive sound often only requires a little EQ and reverb to make it sound right. In this respect, a short reverb with a fairly bright character is ideal for rhythmic parts or staccato playing, as it adds a sense of space and impact without making the mix sound cluttered or messy. Longer reverbs, or combinations of delay and reverb, can be used for more languid guitar parts. Further movement can be added by feeding the effects send through a chorus or flange unit before it gets to the reverb unit. This is easy to do using Logic by inserting the modulation effect directly before the reverb plug-in in the Buss Audio object being used as a return.
Slightly less common treatments include feeding the guitar through the rotary-speaker simulation from the Logic tone-wheel organ plug-in or (one of my favourites) feeding it through the stereo vibrato plug-in adjusted to give square wave chopping at eight or 16 pulses to the bar, sync'ed to the Song tempo. I've used this trick to turn simple chordal guitar parts into integral parts of the rhythm track in all styles of music, from dance to mainstream pop. If you also filter out some low end, what you end up with is almost like a melodic hi-hat part, especially if the source is a bright, clean guitar sound.
Another trick I've experimented with is playing solo guitar lines that include string bending through Logic's Pitch Correction plug-in. Set normally, this ensures all notes are bent to the nearest correct semitone, but you can also speed up the correction rate to produce a mild 'yodelling' effect that gives the sound a slightly Eastern flavour. This may be even more effective if you set up your own custom scale based on an Arabic note sequence.