Now that we’ve covered general matters of mic choice and placement have been covered, as well as instrumental and room acoustics, it’s time to consider specific instrumental situations. Keep in mind that the ideas given here are only guidelines - the exact methods you’ll use will depend on such things as your intended tone, the instrument, musical style, the performer and the acoustic context.
While preparing your mic setups, don’t lose sight of other ingredients that will make or break the success of your session. Things like tuning, instrument preparation/setup, creature comforts of the players, and the tonal concept you’re shooting for (and may need to discuss with participants before setting up).
Basses – Electric and Acoustic
The electric bass guitar is recorded direct to tape using a DI (direct inject) box. This technique produces a very clean recorded signal. Since it involves no amplifier in the studio, it also keeps the bass guitar from bleeding into the microphones of other instruments.
But recording the bass guitar only through a DI box does not guarantee a good tone or a happy player. The DI sound can seem quite plain (some might say “lifeless”) since it does not generate the electronic interaction and tonal nuance that are a part of the guitar/amplifier combination. Many performers rely on amps for sculpting their particular tone; even after experimenting with EQ on the DI signal you may not achieve the sound you’d want to hear from the bass player’s bass amp.
Many bass amps now include a DI output after the preamp. That’s still not the same as miking a speaker that’s fed by the bass amp – these DI outputs provide a signal that is not modified by either the amplifier or speakers. In fact, some of these DI outputs sound quite harsh and must be run through a low pass filter to roll off the high end. In some instances this function is included on the amp as well. It often masquerades as “speaker compensation” or “speaker emulation”. Similarly, using a separate DI box can sound excessively trebly and must be EQed to taste.
An effects send can sometimes be used as a recording source if there is no dedicated output. In some amps, inserting a connection into the output jack will break the connection to the amplifier section, and no sound will come from the amp, even though signal will be recorded. In other models, the signal will be split and travel to both the amp and the recorder. Depending upon whether acoustic output is desired, this may or may not be a concern. Also, as these effect outputs are often unbalanced, a line amp or separate DI must sometimes be used if the signal is to be run very far.
A final popular method which avoids cranking too much bass into the tracking room is to use a dedicated bass effects processor. These act as DIs but also include amp and speaker emulation as well as effects and dynamics control.
Electric bass miking techniques
None of the DI style methods yet mentioned captures the full acoustic sound from the speakers of the amp. In circumstances where that is really what’s required, a microphone must be used. Generally, a large diaphragm dynamic with plenty of low-end response is a good choice.
A mic and position should be selected so that enough treble is captured in the sound so as to make attacks clear in the mix as well as let the bass be heard on playback systems with smaller speakers. Generally, electric bass parts sound clearest when very little room sound is involved. Close miking the bass cabinet and keeping the sound from bleeding into other instruments microphones are both essential. Try either facing the mic directly into the center of the speaker or slightly off center. Each will lend a particular coloration. Angling the microphone slightly may also produce good results. Pick the one that works best for the session… with that particular player, instrument, amp, mic and space.
A combination of DI and miked signals can produce a great sound. However, be careful when combining these types of signals as they can produce comb filtering effects due to phase interference. To minimize this, record each to separate tracks and try phase inverting or delaying one of them when mixing (by single samples or microseconds).
Using a mic directly on the bass itself, rather than an amplifier, can achieve a sound with lots of string slap, pick, and transient tones. When mixed with a recorded DI track, this can be very useful. Of course, to record this way, the bass must be isolated from the sound of the amplifier or played without an amp.
Miking the acoustic upright bass
The upright bass has two nice “f” holes, one on either side of the strings. A mic placed from 6 inches to two feet in front of one of these can pick up a good balance of the instruments key elements. The closer the mic, the more low frequency information there will be. For extra treble, the mic can be positioned closer to the bridge, or just angled towards it.
Compared to what we’ve discussed with the bass, there’s a much greater tradition of complexity and flexibility when it comes to recording electric guitar. This is due, in part, to their popularity, frequency range, and greater need for an acoustic and spatial context.
While electric guitar can be recorded by DI like the bass, it is much more often recorded with a mic on an the amp/speaker. Amp emulators have also become a popular method for getting guitar tones recorded. Despite this, many guitarists, recording engineers and producers, however, still prefer the sound of the real thing. Directly recorded signals (DI or simulator) can be sent back to the amplifier and rerecorded in a process called reamping. Doing this right (sending a line-level signal back to the amp) requires matching impedance and level so that the amp receives a signal close to that originally produced by a guitar, and responds accordingly. There are many dedicated reamping devices on the market now that can help bridge this electrical divide.
Single microphone recording
The most common method for recording a guitar amplifier is by close miking the speaker cone. This is usually done using a dynamic mic, but some of the more recent condenser and ribbon mics can also handle the high SPLs of raging guitar cabinets. Where there is more than one speaker in a cabinet, choose the one which produces the desired tone most closely.
There are three main considerations in close miking speakers: distance, position and angle.
Distance is the amount of space between the mic diaphragm and the speaker cone (or sometimes the grill). For close miking situations, this is generally 2 to around 9 inches. That is close enough to maximize sonic isolation from reflections while helping to isolate the mic from other instruments and sounds in the room. As the microphone is moved back much beyond one foot, it starts to pick up more of the room.
Position refers to the relative position of the diaphragm within the circle of the speaker cone. If a mic is positioned so that its diaphragm is directly in front of the center of the speaker cone, it is said to be on-center. If the mic diaphragm is not directly in front of the center of the cone, but is still within the area of the circle, it is off-center. The shorter the distance from the speaker to the mic, the greater the influence of position is on tonal coloration. Generally speaking, an on-center position yields a brighter sound than off-center.
An alternate method of placement worth noting is to place the microphone behind the speaker. Obviously, this works best on speaker cabinets which have an open back. This method offers both tonal variation and additional isolation possibilities.
Angle describes the direction the diaphragm is facing relative to the overall surface (in 2 dimensions) of the speaker cone. If the mic is facing directly into the speaker it is said to be on-axis. In this situation, the most sensitive angle of the mic is aimed directly at the speaker. Generally, this means that the mic diaphragm itself is parallel with the speaker. If the mic is turned so that the most sensitive angle is not facing the speaker directly, then it is off-axis. The amount that it is angled away can be described in degrees (good ol’ geometry again).
It is a combination of these three basic elements, along with the influence of the particular microphone and preamp, which determines how a guitar tone is colored by a single mic setup.
Single close-mic setups generate clear, isolated tracks with little of the acoustic signature of the room. When room sound is also desired, one or more additional mics can be set up away from the speakers, to capture the sound of the acoustic space itself. These mics, called ambient or room mics, can be used to add back (to taste) the natural sense of space at mixdown.
Greater variation in tone, image, and space can be achieved by adding a second or third microphone to one of the previous setups on the same speaker, or on a separate speaker. By varying the type, distance, position, or angle, of the second mic, two different colors can now be captured and mixed together later. Panning each to opposite stereo positions can achieve a larger-than-life sound. Again, watch out for phase cancellation when the two tracks are summed to mono.
Miking the rear of the cabinet with a second mic also requires careful phase adjustments. When mics are placed at equal distances from both the front and the back of the speaker, one of them must be phase inverted to avoid extreme cancellation when summed to mono. When mics are placed at slightly different distances from front to back, the interference issues cannot be so easily addressed. (time/phase alignments can be done using very short delays or by sliding regions during editing on a DAW. See TCRM 32 for more…)
Some guitar amps actually send two distinct signals when attached to two or more speakers, and so are said to be “stereo.” In a situation like this, it can be useful to record each sound by close-miking two speakers producing these different sounds. On mixdown, these two tracks can then be panned to opposite sides.
Control room recording
Tone is everything. If the guitarist hears his or her favorite tone while playing, the performance will be worth recording. Tone does not depend on size and loudness of the amp – small amps can deliver exquisite tone, hopefully at levels that keep ears and neighborly relations intact.
During guitar overdubs, when constant communication between recordist and player is desirable, you may want to mike the speakers in the tracking room, invite the player into the control room, and have him or her perform to the sound of your studio monitors at a reasonable volume. Rig up a long guitar cord or hook up via one of the studio tielines. This insures that the player performs to the tones that are being recorded since the loud sound in the tracking room will differ somewhat from the sound coming from your monitors in the control room. When player and engineer are in agreement on the recorded tone, and in close communication, the session is likely to progress more quickly and achieve a successful result.
Acoustic and classical guitars
Classical and other types of acoustic guitars vary widely in size, shape, bracing, internal volume, woods and strings used. This creates great variations in the overall tonal characteristics between models, even between individual instruments of the same model. It also effects which aspects of that tone a mic will pick up from a given location, particularly when placed close to the instrument. The guitars large body size and numerous resonating areas can produce many drastically different timbres depending on the location. As a mic is moved around the body of the guitar, not only does it travel in and out of modal hot spots, it also captures a different balance between the various resonating parts.
While there is no one position for placing a mic to get the “perfect” tone, there’s a wealth of possibilities for tonal color. Rather than swapping mics or instruments, or relying on EQ to modify the timbre of an acoustic guitar, simply moving the microphone to a different location may do the trick. Microphone choice will determine whether a tonal color is possible (if your in the ballpark) but it’s the placement that will achieve the specific timbre you are after. Placing your mics too close to acoustic guitars, however, yields an unbalanced sound. As a rule, six inches to two feet should be considered close enough.
Condenser microphones, especially small diaphragms, are often used for their great transient response and ability to reach into the extended frequency ranges required by acoustic guitars.
Some generalizations regarding relative placement:
When recording a steel-stringed acoustic guitar, placing the mic around seven inches to a foot away from the face, just below the sound hole, can capture a more balanced tone. From this position, angling the mic towards the sound hole will accentuate the bass, if desired. Be aware: placing the mic directly over (or too close to) the sound hole will generate a sound with too much bass. This is because of the lower resonant frequencies of the internal volume of air combined with the proximity effect generated by close miking.
Moving or pointing the mic towards the bridge will pick up a brighter, more trebly sound. Likewise, moving, or pointing, the mic towards the neck will capture a more mellow tone.
Classical style guitars require a slightly different approach due to their nylon or gut strings and smaller body size. Placing the mic around 9 inches back, directly in front of the bridge, will add a brightness which is needed in classical guitars. If more bass is needed, the mic can be angled or moved towards the sound hole.
If the performance takes place in a great acoustic space and the natural reverb of the room is desired, there are a couple methods for achieving this. First, a figure eight pattern mic could be used in the same position just described. This would combine the close feel in the front with the reverberant sound from the rear of the mic. A stereo pair of microphones placed further back can also do a great job of capturing the acoustic signature of the space (more on stereo miking in TCRM 11).
Brass and Wind Instruments
‘Pets and ‘Bones
Trumpets and trombones are LOUD!!! Only dynamic mics or high SPL condensers should be used for close-miking techniques. Often, placing the mic a distance of a foot or more in front of the bell (flare) is a good idea. A wind screen is also needed to protect against rushes of air, which can create rumble in the audio. Even with these precautions, however, moving the microphone slightly to the side of the direction of the bell is sometimes necessary. Beware, however, that since the bell generates a very directional radiation pattern for the sound, especially in the higher frequencies, moving too far to the side will reduce pickup of the higher frequency partials.
Trumpets played with the Harmon mute (for the “Miles Davis” sound) are usually played very close to the mic, to capture the weak but characteristic piercing overtones. This can create inordinate proximity effect. Communicate with the player to find an acceptable distance from the mic, and – if the part calls for alternating open and muted passages – consider setting up a separate omni mic (there’s no proximity from an omni) for those muted passages, recorded to a separate track.
In the concert hall, French horns are most often heard only in reflection. Since the bell points to the rear (under the players right arm), the sound first travels to the rear wall before bouncing back to the audience. For this reason, the French horn is best recorded in a manner that stresses reflections and/or reverb fairly heavily. This can be done by placing a directional mic in front, and slightly to the side, of the instrument. This stresses the first order reflections from the rear wall. Placing a figure eight or omni mic between the bell and the rear wall can also be a good method for combining direct and reflected sound. Finally, miking the space itself with figure eight or omni microphones can be handy in getting that special acoustic signature.
Of course, a close miking technique could be employed when needed, especially if used in conjunction with a good reverb algorithm, but the French horn is almost unrecognizable when miked close to the bell. The listener needs to perceive quite a bit of diffuse room sound to recognize the typical French horn section sound.
This is less applicable when a French horn is used as a solo instrument, or in a Big Band setting where close-miking is inevitable. Check with the player and/or producer before settling on a given recorded sound, to make sure that the sound you’re about to capture is acceptable to them.
The big guys
So as not to forget them, tubas, sousaphones, baritones and the other low-end brass instruments all require a bit of space between the bell and the mic for a natural sound. Often, three feet is a good compromise distance.
Miking for woodwinds
Unlike brass instruments, woodwinds generate and radiate most of their sound along the length of the instrument and not so much from the bell alone. The holes that the player leaves open or covers up change the length of the vibrating air column inside the instrument. This makes extreme close-miking impractical as sound emanates from various points along the instrument as he or she plays different notes. The mic should be placed where it can pick up sound equally from all holes in the instrument.
The ideal mic location is not the same for all woodwinds, however, and further considerations involving the bell, tone holes, breath, formants, key clicks, and the mouthpiece, make it difficult to generalize. Furthermore, the relative balance of each of these elements can be adjusted to either accentuate or reduce other aspects of an instrument’s particular tone. The project will determine your approach – is the instrument supposed to sound “airy” as in an orchestral context, or up close like a solo instrument in popular music.?
Because they use holes in the body of the instrument to change their effective acoustic length, the point from which the sound emanates, changes. This means that they should not be miked too close, as certain notes and partials, specific to that location along the instrument, will be stressed. It also means that the mic should be placed somewhere it can pick up sound equally from all holes in the instrument. Though certain (usually more distant) placements may achieve a more “natural” representation of the sound, in a creative recording environment this is not necessarily what is desired.
For popular music, a good placement for the mic is between the mouthpiece and the middle keys, eight to twelve inches away and slightly above the flute’s level. This gives a nice balance between breath and mouthpiece sounds and the tone holes themselves. A pop filter or wind screen may be necessary to stop wind noise and rumble. Greater balance and a more “natural” tone can be achieved by moving the microphone further away.
Given the curve of the sax, the bell actually comes back towards the center of the instrument. This means that a placement of around 1 to 2 feet away, and around 1/3 of the way down the instrument, works quite well, especially when angled slightly towards the bell. Though key clicks are sometimes considered to be a part of the instruments charm, they can be reduced either by distance, or by angling a close (ca. 8 inches), unidirectional mic downward toward the bell.
The clarinet produces three distinctive timbres. In its lowest octave the sound is rather dark and woody, the next octave is somewhat muted, even a bit choked, and the upper range projects a more open and downright piercing sound. Experienced jazz players on stage adjust their stance instinctively so that the mic properly captures whatever sound they produce at the moment.
In a studio situation, aim for a compromise, with a microphone that is perpendicular to the body of the instrument and placed around 2/3 to 3/4 of the way down, and at least 6” to 1’ away. The mic can be angled upwards to pick up more from the body and less from the bell. This will serve to even out the notes while rounding off the higher frequency formants emanating from the bell.
TCRM 11 will discuss stereo miking techniques as well as methods for miking drums and pianos.
John Shirley is a recording engineer, composer, programmer and producer. He’s also on faculty in the Sound Recording Technology Program at the University of Massachusetts Lowell.
Check out his wacky electronic music CD, Sonic Ninjutsu, at http://www.cycling74.com/c74music/009.
Supplemental Media Examples
TCRM 10 discusses miking techniques for guitars, basses, brass and wind instruments, so the following examples are demonstrations of how mic choice and placement affect some common examples of these. Special thanks to Connor Smith for helping run the sessions as well as playing both the bass and the guitar recorded here. Thanks also to Shauna Barravecchio who played both flute and piccolo, Eric Dion who played sax and Reynaldo Santana who played trumpet; you all rock!
First, let's compare two recordings of an electric guitar miked with an SM57 cardioid dynamic microphone. First right in front of the center of the speaker cone and very close to the grill; then at 20-inches back from that same spot.
E. Guitar, SM57, close, centered, on-axis: TCRM10_1.wav
E. Guitar, SM57, 20-inches, centered, on-axis: TCRM10_2.wav
Now, let's hear what the close SM57 would sound like angled at 45-degrees and slightly to the right of center of the speaker cone. First with a reminder of what the on-axis, centered sound was:
E. Guitar, SM57, close, centered, on-axis: TCRM10_1.wav
E. Guitar, SM57, close, centered, 45-degrees off-axis: TCRM10_3.wav
What if we were to try a different mic, a Beyer M160 hypercardioid ribbon mic, angled similarly to the last: TCRM10_4.wav
*See included picture of mic setup during recording.
A different sound, also with a bit more of the sound of the room, can be obtained by moving the mic even further away from the speaker. Here, a Neumann TLM103 large-diaphragm condenser is placed on-axis four feet in front of the speaker: TCRM10_5.wav
Finally, the guitar is recorded from nearly 20-feet away with the mic placed in another corner of the room (here, a DPA 4006 omnidirectional small-diaphragm condenser): TCRM10_7.wav
Now let's listen to some variations on recording the bass.
Here, the bass is recorded using the close-miked SM57 techniques used above, first on-axis and then 45-degrees off.
E. Bass, SM57, close, centered, on-axis: TCRM10_8.wav
E. Bass, SM57, close, centered, 45-degrees off-axis: TCRM10_9.wav
A mic is placed further out in the room, as was done in the last guitar example (again with a DPA 4006): TCRM10_10.wav
Another common method for recording electric bass is the use of a DI. Below are some variations.
The DI output straight off the back of the amp head: TCRM10_11.wav
A Countryman DI: TCRM10_12.wav
A Behringer DI-100 DI: TCRM10_13.wav
A Whirlwind Director DI: TCRM10_14.wav
We also recorded a variation using a little more gain and the DI on the amp head: TCRM10_15.wav
That version was simultaneously recorded using a Crown PZM30 microphone taped to the floor several feet in front of the speaker cabinet: TCRM10_16.wav
Here, a trumpet is recorded using four variously-placed Neumann TLM103 large diaphragm condensers. Again, note the differences in tone based on distance and/or position in relation to the instrument, especially the bell.
Straight on at 3-feet away: TCRM10_17.wav
Straight on at 9-inches away: TCRM10_18.wav
9-inches away, but off towards the side at 45-degrees from the bell: TCRM10_19.wav
9-inches away, but off to the side at 90-degrees from the bell: TCRM10_20.wav
Now, the trumpet again with various mics at 3-feet on axis....
A DPA 4006 omnidirectional small-diaphragm condenser: TCRM10_22.wav
A Royer R121 bidirectional ribbon mic: TCRM10_23.wav
Again, a room mic is used far away (still a DPA 4006): TCRM10_24.wav
As with the trumpet, a set of four TLM103's is used to record an alto sax. Listen to the differences in tone based on placement and distance.
First, close to (and facing into) the bell: TCRM10_25.wav
Then close to (and facing) the keys above the bell: TCRM10_26.wav
Now, about 9-inches off to the side at 45-degrees: TCRM10_27.wav
Finally, straight on but 2-feet out: TCRM10_28.wav
An array of four different mics is now used on-axis and three feet out in front. Listen to the differences the various microphones and polar patterns make....
A Beyer M160 hypercardioid ribbon mic: TCRM10_31.wav
A DPA 4006 omnidirectional small-diaphragm condenser: TCRM10_32.wav
Now the four TLM103s are used on the flute at various distances and positions.
In front of the mouthpiece: TCRM10_33.wav
About a foot above the center of the instrument: TCRM10_34.wav
About 3-feet above the center of the instrument: TCRM10_35.wav
Two feet out front and above the instrument: TCRM10_36.wav
And, for consistency, the DPA 4006 out in the room again: TCRM10_37.wav
Lastly, our four TLM103s are used to record piccolo at various distances and positions.
In front of the mouthpiece: TCRM10_38.wav
About a foot above the center of the instrument: TCRM10_39.wav
About 3-feet above the center of the instrument: TCRM10_40.wav
Two feet out front and above the instrument: TCRM10_41.wav
And the DPA 4006 out in the room: TCRM10_42.wav