Here is a selection of audio files to accompany this month's Acoustic Guitar Recording (/sos/apr10/articles/acguitar.htm).
In this article you'll find links and full descriptions for all the audio files created to accompany this month's acoustic guitar recording feature. The files fall into four sections: Mic Shootout, Guitar Dispersion, Alternative Mic Positions, and Mixing Demonstrations. The best way to audition these files is to import them all into your DAW for side‑by‑side comparison, and this also means that you can experiment with mixing different mic models and placements, as many producers actually do in practice.
Mic Shootout
The first set of audio examples (filenames beginning 'Mic') illustrates the character of a range of different microphones that have been frequently mentioned in SOS's producer interviews when discussing the subject of acoustic guitars. A total of nine microphones were simultaneously used to record three different guitars from a position roughly 18 inches in front of the guitar. The mics were set up in as close a pattern as possible, all pointing roughly at the join between the guitar's neck and body. The identity of the mic used for each file can be ascertained from the third section of the filename, as follows:
4038: Coles 4038 ribbon mic, which has by nature a figure‑of‑eight polar pattern.
C12: AKG C12 multi‑pattern large‑diaphragm valve condenser mic, switched to its cardioid polar pattern.
C414BULS: AKG C414B‑ULS multi‑pattern large‑diaphragm condenser mic, switched to its cardioid polar pattern.
C451: AKG C451 small‑diaphragm condenser microphone fitted with its CK1 cardioid capsule.
SE4: SE Electronics SE4 medium‑diaphragm condenser mic fitted with its cardioid capsule. This mic was included for comparison purposes, because it is used for subsequent mic‑positioning examples.
SM57: Shure SM57 cardioid dynamic mic.
U47: Neumann U47 multi‑pattern large‑diaphragm valve condenser mic, switched to its cardioid polar pattern.
U67: Neumann U67 multi‑pattern large‑diaphragm valve condenser mic, switched to its cardioid polar pattern.
U87: Neumann U87 multi‑pattern large‑diaphragm condenser mic, switched to its cardioid polar pattern.
Because all these mics were recorded together, you can experiment with how their different flavours mix and match. The signal waveforms have all been checked for identical polarity and the coincident miking position means that the different mic signals are fairly well time‑aligned, so you should be able to combine the different microphones without serious phase cancellation. All the microphones were recorded for three different guitars, and you can tell which guitar is used from the second section of each filename as follows:
Gtr1: A Taylor The DI output of this guitar was also recorded alongside the mic signals (filename 'Mics_Gtr1_DI'), allowing you to experiment with mixing in the DI signal alongside different mic flavours. Note that the DI signal arrives slightly in advance of the mic signals, because of the delay involved in sound passing from the guitar strings through the air to the mics, so you may wish to slide this waveform earlier in your sequencer to achieve a better phase match.
Gtr2: An Art & Luthiere.
Gtr3: A Huss & Dalton.
Guitar Dispersion
The second set of audio examples (filenames beginning 'Disp') use multiple SE Electronics SE4 medium‑diaphragm condenser microphones (with cardioid and omni polar patterns) to demonstrate how different aspects of the guitar's tone are captured from different mic positions. The microphone position for each file is shown by the third and fourth sections of each filename as follows:
Bridge_ClsCard: A cardioid mic roughly nine inches from the front of the guitar, aimed at a point a little left of the instrument's bridge. Here the body resonances are more pronounced.
Frets_ClsCard: A cardioid mic roughly nine inches from the front of the guitar, aimed at the fifth fret. Here the sound of the strings is emphasised, along with fretting noises and occasional string buzzes.
OnSH_ClsCard: A cardioid mic roughly nine inches from the front of the guitar, aimed directly at the soundhole. The instrument's air resonance is emphasised in this location, as well as the pick noise.
OverSH_ClsCard, OverSH_MidCard, OverSH_FarCard: Cardioid mics located in front of the guitar and located above the level of the soundhole, angled downwards to aim at a point a little above the soundhole. This general position is one of the two most commonly cited in my survey of producer interviews, so I've also set up mics at different distances from the instrument to give an idea of the different timbral variations you can achieve in this way: 'ClsCard' is at roughly nine inches away, 'MidCard' at roughly 18 inches, and 'FarCard' at roughly three feet. Notice how the mic picks up a more holistic sound of the instrument as it's moved away, but how at the same time the level of proximity‑effect bass boost decreases and the amount of room ambience increases.
OverSH_ClsOmni: As 'OverSH_ClsCard', except using the mic's omni capsule. Notice how this picks up a more balanced view of the instrument, but at the same time a greater level of room ambience.
UnderSH_ClsCard: As 'OverSH_ClsCard, except with the mic under the level of the soundhole, rather than above. The tonality achieved is nonetheless dramatically different.
Vanilla_ClsCard, Vanilla_MidCard, Vanilla_FarCard, Vanilla_ClsOmni: Cardioid and omni mics located in front of the guitar a little over the fretboard and angled inwards to aim at the point where the guitar's neck meets its body. This position is probably the most frequently recommended recording technique for recording acoustic guitars, as it enables a balance to be achieved between the sound of the strings themselves and the resonance contributions of the body and soundhole, depending on the exact location and orientation of the mic. As with the 'OverSH' examples, I've taken the opportunity to demonstrate how the sound changes for this position with distance and changing polar pattern. Again, 'ClsCard' is roughly nine inches away from the instrument, 'MidCard' is roughly 18 inches away, and 'FarCard' is roughly three feet away. The 'ClsOmni' file positions an omni mic as close as possible to 'Vanilla_ClsCard' for comparison.
This entire multi‑mic rig was recorded with the same three guitars as before, and a DI signal was again captured alongside the mics for the 'Gtr1' files. In addition two further sets of 'Gtr1' audio examples were recorded with the Taylor guitar, the first denoted 'Gtr1Baff', in which the Taylor guitar and multi‑mic rig were surrounded with numerous acoustic panels and blankets to significantly deaden the otherwise live acoustic of the drum room in Livingston Studio One. Reflections from both the wooden floor and the stone walls were tackled, and the change in sound is clearly audible in the recordings. Notice in particular how the more distant mics become tighter‑sounding, and also how the sonic variations between the closer mic positions become exaggerated, such that the exact choice of mic position becomes more critical. The second additional set of files is denoted 'Gtr1Refl' and here the Taylor guitar and its multi‑mic rig were surrounded with a number of hard‑surfaced panels angled to reflect more of the sound of the guitar back into the mics, a technique I discussed in the article.
Alternative Mic Positions
This third set of audio examples (filenames beginning 'Alt') showcases some alternative mic positions worth considering alongside the two primary ones already covered in the 'Disp' files. The mic position for each file is denoted by the third section of the filename as follows:
EarL, EarR, EarSt: Cardioid mics were positioned either side of the performer's head looking down on the instrument from above. The mics were roughly 12 inches away from the guitar and were slightly forward of the line of the instrument's front panel to avoid high‑frequency shadowing of the strings by the performer and the instrument's body. The 'EarL' and 'EarR' files are to the left and right of the performer respectively from the audience's perspective. A composite file, 'EarSt' is a mix of 'EarL' and 'EarR' panned slightly off centre to give a slightly wider guitar image in the stereo field.
OverSH: A cardioid mic roughly 12 inches from the guitar, positioned as for the similarly named files in the 'Disp' set. This file is for comparison and mixing with the other alternate mic techniques here.
OverTail, UnderTail: Two cardioid mics positioned around the tail of the guitar pointing roughly towards the soundhole and slightly in front of the front panel to reduce high‑frequency shielding from the instrument's body and from player's right arm. These two positions have the advantage of being a long way from the fretboard, which can help reduce unwanted noises when recording soft fingerpicking parts.
VanillaCls, VanillaMid, VanillaFar: The first of these files is a cardioid mic roughly 12 inches from the guitar, positioned as for the similarly named files in the 'Disp' set. 'VanillaMid' and 'VanillaFar' are positioned two and four inches further away respectively to demonstrate the role that phase‑relationships can play in multi‑mic rigs. First compare the differences between the each of these mics in solo, so that you have an idea of the difference that the position change alone is making. Now try mixing 'VanillaCls' with one of the other mics (for example 'OverSH'), and then switch 'VanillaCls' for 'VanillaMid' or 'VanillaFar' to get a feel for how the changing phase‑relationship between the mixed mics can alter the sound.
XYL, XYR, XYSt: A pair of cardioid mics set up in an XY coincident configuration around 12 inches away from the front of the guitar, centred roughly on the point when the instrument's neck meets its body. Although at this distance both mics pick up quite a lot of the instrument, you can nonetheless hear how the left‑facing mic is picking up more of the soundhole/body components, while the right‑facing mic is catching more of the string noise, which means that mixing the two mics together provides a degree of tonal control after recording. (Closer mic placement emphasises this difference between the mics, albeit at the expense of a slightly drier and less natural sound.) The 'XYSt' file is a mix of 'XYL' and 'XLR' with the two mics panned a little off centre to give a little width to the stereo image.
Mixing Demonstrations
The final set of audio examples (filenames beginning 'Mixing') demonstrate some of the mixing techniques I mentioned in the article. The examples with filenames containing 'GtrMix' show a few of the ways you can enhance a fairly respectable guitar recording:
Unprocessed: Here is a mono mix of two of the different mics recording the Taylor guitar in the 'Disp_Gtr1' file set: primarily 'UnderSH_ClsCard', with a lower level of 'Vanilla_CloseOmni'. Beyond balancing the levels of the mics against each other, no processing has yet been applied.
LowRatioComp: Low‑threshold (‑33dBFS), low‑ratio (1.8:1) compression from URS Console Strip Pro has been used here to even out the performance dynamics slightly and to subtly increase sustain. Despite up to around 5dB gain reduction on occasion, the combination of medium attack time (10ms) and programme‑dependent automatic release ensures that the the transients and short‑term dynamics remain pretty natural.
WarmReverb: A straightforward short Room reverb from Lexicon's Pantheon II plug‑in has been used to gently widen and warm the compressed acoustic guitar sound of 'LowRatioComp'. In order to avoid cluttering the sound or creating distracting echoes of pick noises, the response of the reverb has been curtailed with both high‑pass and low‑pass filters in the return channel.
MicroReverb: Compare the tonality of this file with 'LowRatioComp', and you can hear that it's quite different. However, the difference was achieved through extremely short reverb rather than via EQ: because of a lack of any predelay the early reflections following the dry signal occur early enough to colour the sound through comb‑filtering, but the reverb is too short to be heard as any kind of 'tail' in its own right.
SubtleChorus: Another tactic for smoothing and widening an acoustic guitar recording is applying a small amount of a stereo modulation effect. In this example I've used a simple low‑level chorus effect to spice up the 'LowRatioComp file'. It's worth comparing this not only to the dry 'LowRatioComp' file, but also to the 'WarmReverb' example.
The 'BoomTick' examples illustrate how you might deal with a couple of the most common problems with less‑than‑ideal acoustic guitar recordings:
Unprocessed: This is the sound of a mic pointing directly at the soundhole, and as such has a good deal of unevenness in the volume of the lowest notes as well as too much pick noise. No processing has yet been applied to this mic so that you can use it for comparison against the other files.
NotchEQ: The low‑frequency unevenness is on account of the sound‑hole resonance, which is unmusically amplifying the fundamental frequencies of a couple of notes. Extremely narrow‑band 7.5dB EQ cuts focused on these two fundamental frequencies (100Hz and 111Hz respectively) helps even this up, but at the expense of a certain hollowness in the sound. For better results, these notch EQ bands could be activated only when the offending notes occur.
PickComp: One method of reducing pick noise is to use a fast‑attack compressor to target the pick transients, and that's what I've now done to the 'NotchEQ' example using URS Console Strip Pro. The plug‑in's Dbx 160 model has been set to a 4:1 ratio with attack and release times of 0.1ms and 4.9ms respectively.
PickMultiComp: You can achieve greater control over high‑frequency attack transients such as pick noise using the high band of a multi‑band compressor. This example applies such processing to the 'NotchEQ' example file using Cubase 5's built‑in Multiband Compressor plug‑in, processing a region above 4kHz with a 5.5:1 ratio and attack and release times of 0.1ms and 10ms respectively.
PickTrans: Another tactic for targeting pick noise more aggressively is to use a dedicated transient processor. This audio example uses the plug‑in version of SPL's Transient Designer to process the 'NotchEQ' example in this way, dramatically reducing the levels of the pick transients.
The 'FretNoise' examples show one approach to dealing with one of the most challenging of acoustic‑guitar salvage tasks: the reduction of excessive fret noise:
Unprocessed: Here's a recording that includes extremely high levels of fret noise, which detract from the performance.
AutoEQ: One of the only effective ways to deal with the problem, in my experience, is to automate a high‑frequency EQ cut just during the periods of fret noise to take the edge off them. That's what I've done for this example, using 12‑24dB of cut from a 2.3kHz high shelving filter in Cubase 5's built‑in channel EQ for the purpose..
