Notes · Music TechnologyUK · A-Levels

Microphone placement techniques

Where a microphone is placed matters as much as which microphone it is. This topic covers single miking and the working-distance decisions it involves, then the stereo techniques - coincident (XY, Blumlein), spaced pair (AB), the near-coincident ORTF, and mid-side - each capturing a stereo image in a different way. It closes with multi-microphone setups and the phase problems they create, the 3:1 rule that avoids them, and the comb filtering that results when the rule is broken.

5 sections~20 min reading time3 competenciesLevel Foundation 1 · Standard 2 · Advanced 2

T·0555 / 16

Exam profile

C1 · Place single and stereo microphone arrays (XY, AB, ORTF, MS) and predict their stereo imageC1 · Plan a multi-microphone setup and avoid phase problems using the 3:1 ruleC3 · Explain comb filtering and spill and their effect on a recorded sound

Operators:describeexplaincompareplanjustify

basic level

The AS foundation is single miking and the difference between coincident and spaced stereo pairs.

higher level

The full A-level adds ORTF, mid-side and its decode, and the phase, 3:1-rule and comb-filtering reasoning of multi-mic setups.

Depth

Text

Contents · 5 sections

Microphone placement techniques

Single miking: choosing position#

FoundationPearson 9MT0 - microphone placement techniques

Single miking a guitar cabinet

Fig. 1A single microphone on a source: distance, axis and the spot on the source are chosen for tone. On-axis and close gives the brightest, most present sound.

The simplest and most common technique is a single microphone on a single source, and its position is a powerful tonal control. Three things are chosen: the distance (close for isolation, presence and proximity warmth; distant for a natural, roomier sound), the axis (whether the microphone points straight at the source, on-axis, or off to one side, off-axis), and the exact spot on the source it faces. Small moves change the balance of frequencies, direct and room sound, and detail dramatically.

On-axis versus off-axis placement changes the tone because most microphones are brighter and more detailed on-axis and progressively duller off-axis (their high-frequency response falls off the sides). Angling a microphone off-axis is therefore a way to soften a harsh source or tame sibilance without EQ, while pointing it straight on captures the fullest high end. The position on the source matters too: on a guitar cabinet, aiming at the centre of the speaker cone gives a bright sound and aiming at the edge gives a warmer, mellower one.

Distance sets the direct-to-room balance and the level, and it interacts with the proximity effect on directional microphones. Close in, you get isolation, presence, a strong level and (on a directional mic) a bass lift; further back you get more room, a more natural perspective, a lower level and less proximity bass. Because doubling the distance drops the level by about 6 dB and roughly doubles the room content, distance is a single control trading presence and isolation against ambience.

The source's own radiation pattern must be considered, because instruments do not sound the same in every direction. A guitar's body projects bass, its neck the string detail; a saxophone throws high frequencies out of the bell and body sound from the keys; a drum sounds different above the head, at the edge and underneath. Moving the microphone around the source, and listening, is how the wanted blend of an instrument's several 'sounds' is found - the essence of single-mic technique.

For the exam, be able to justify a single-microphone placement in terms of distance, axis and position: what tone and balance each achieves, and how you would move the microphone to solve a specific problem (too bright, too boomy, too roomy, too little body). Single miking underlies everything - even complex setups are combinations of well-placed single microphones - so the reasoning here recurs throughout the topic.

Worked example

Placing one microphone for tone

A single microphone on a guitar cabinet sounds too bright and harsh. Describe two placement changes to warm it up.

Move off the centre
Move the microphone from the centre of the speaker cone toward the edge, where the cone radiates fewer high frequencies, for a warmer tone.
Angle off-axis
Angle the microphone off-axis to the cone, so its high-frequency response rolls off, softening the harshness without EQ.
Consider distance
Backing off slightly reduces the proximity bass but also captures a little more room, giving a rounder, less in-your-face sound if needed.
Confirm by ear
Audition each move; the combination of edge position and off-axis angle typically removes the harshness while keeping the body of the sound.

Result: Move toward the cone edge and angle off-axis (and back off slightly) to warm and de-harsh the sound - tonal control by placement alone.

Typical mistakes

Treating microphone position as fixed - distance, axis and spot each change the tone substantially.
Ignoring off-axis dulling: angling a microphone off-axis softens the high end, a useful tonal tool.

Active revision

Describe how you would place a single microphone on a guitar amplifier to get (a) a bright sound and (b) a warmer sound, explaining the position and axis in each case.

Active recall

Recall the key points — then reveal.

Sources: Pearson Edexcel Level 3 Advanced GCE in Music Technology (9MT0) Specification (Pearson Edexcel)

Coincident stereo (XY, Blumlein)#

StandardPearson 9MT0 - microphone placement techniques

An XY coincident pair

Fig. 2XY: two directional capsules coincident at one point, angled about 90 degrees. With no path-length difference, the stereo image comes from level differences alone - focused and mono-compatible.

Stereo recording uses two microphones to capture a left-right image of a source or ensemble, and the techniques differ in whether they encode that image as differences in level, in time, or both. The coincident techniques place the two capsules as close together as possible - effectively at the same point, one above the other - so there is no time (path-length) difference between them; the stereo image is created purely by level (intensity) differences, because a sound off to one side is louder in the microphone facing that way.

The classic coincident method is XY: two directional microphones (usually cardioids) with their capsules coincident and angled apart, typically between 90 and 135 degrees. A sound from the left is more on-axis to the left-facing capsule and louder there; a sound from the centre is equal in both. Because there is no time difference, XY produces a solid, focused image with excellent mono compatibility - summed to mono it does not suffer the phase cancellation that afflicts spaced techniques - though its stereo width is moderate.

The Blumlein pair is a coincident technique using two figure-8 microphones crossed at 90 degrees. It captures a very natural, precise stereo image and a good sense of the room (via the rear lobes), but it needs a good-sounding room because those rear lobes pick up the space behind. Both XY and Blumlein share the coincident virtue: no time difference means no comb filtering between the microphones and reliable mono compatibility.

The trade-off of coincident techniques is width and spaciousness. Because they rely only on level differences, they can sound narrower and less enveloping than spaced techniques, which add the time differences the ear also uses to judge width and space. Coincident arrays are therefore chosen when a tight, mono-safe, well-focused image is wanted - broadcast, film, and any situation where the recording may be heard in mono - accepting a slightly less spacious sound.

For the exam, the defining facts are: coincident pairs have their capsules at the same point, so they encode stereo by level differences only, giving a focused image and excellent mono compatibility with no comb filtering; XY uses angled cardioids, Blumlein crossed figure-8s. Contrast this with the spaced and near-coincident methods that follow, which trade some mono safety for greater width and spaciousness.

Worked example

Choosing XY for a mono-safe capture

A percussion overhead pair will be broadcast, where many listeners hear in mono. Explain why XY is a safe choice and what is given up.

The mono requirement
Broadcast may be summed to mono, so the technique must not cancel when the two channels are added.
Why XY is safe
XY's capsules are coincident, so there is no time difference between them; summing to mono adds two aligned signals with no comb filtering or cancellation.
What is given up
XY encodes the image by level only, so it is a little narrower and less spacious than a spaced pair, which would add time-difference width.
Decision
For a mono-safe, focused overhead image, XY is the right trade-off; reserve a spaced pair for stereo-only, spacious captures.

Result: XY is mono-safe because its coincident capsules have no time difference to cancel; the cost is a slightly narrower, less spacious image.

Typical mistakes

Thinking XY creates its image from time differences - coincident pairs have no time difference; the image comes from level only.
Spacing the capsules apart and still calling it XY - the defining feature is that the capsules are coincident.

Active revision

Explain why an XY pair remains solid when a recording is summed to mono, and state one situation where you would choose XY over a spaced pair.

Active recall

Recall the key points — then reveal.

Sources: Pearson Edexcel Level 3 Advanced GCE in Music Technology (9MT0) Specification (Pearson Edexcel)

Spaced pair (AB) and ORTF#

StandardPearson 9MT0 - microphone placement techniques

A spaced (AB) pair and the time difference

Fig. 3A spaced (AB) pair: an off-centre source reaches the near microphone first, so the stereo image is encoded by the time difference - wide and spacious but less mono-compatible.

The spaced pair (AB technique) places two microphones - often omnidirectional - some distance apart, from tens of centimetres to a metre or more, facing the source. Because the microphones are separated, a sound off to one side reaches the nearer microphone first: the stereo image is encoded chiefly by time (arrival) differences, with some level difference too. Spaced pairs give a wide, spacious, enveloping sound with rich low frequencies (especially with omnis), which is why they are loved for orchestras, choirs and natural room recordings.

The price of that spaciousness is reduced mono compatibility and the risk of phase problems. The very time differences that create the width can cause comb filtering when the two channels are summed to mono, thinning the sound, and a central source can seem vague ('a hole in the middle') if the spacing is too great. Spaced pairs are therefore chosen when the recording will stay in stereo and a big, immersive sound is wanted, accepting the mono caveat.

ORTF is a near-coincident compromise designed to get much of the width of a spaced pair with much of the mono safety of a coincident one. It uses two cardioid microphones with their capsules 17 centimetres apart and splayed at an angle of 110 degrees. The 17 cm spacing (close to the spacing of human ears) adds time differences for width, while keeping the capsules close enough to limit comb filtering, and the 110-degree angle adds level differences. The result is a realistic, spacious yet reasonably mono-compatible image, widely used for ensembles and location recording.

The three families now form a clear spectrum. Coincident (XY, Blumlein): capsules together, level differences only, focused and mono-safe, narrower. Near-coincident (ORTF): capsules a little apart and angled, both time and level differences, realistic width with fair mono safety. Spaced (AB): capsules well apart, mainly time differences, widest and most spacious but least mono-safe. Choosing among them is a decision about how much width and space you want versus how mono-safe the recording must be.

For the exam, know the defining geometry and behaviour of each: AB spaced omnis encode width by time difference and are wide but less mono-compatible; ORTF is two cardioids 17 cm apart at 110 degrees, near-coincident, realistic and a good all-rounder. Being able to place them on the coincident-to-spaced spectrum, and justify a choice for a given source and delivery format, is exactly what is assessed.

Worked example

AB or ORTF for a stereo-only release

A string quartet is being recorded for a stereo-only download. The producer wants a spacious, realistic image but is nervous about phase. Recommend AB or ORTF and justify it.

Weigh the priorities
Spaciousness favours a spaced approach, but the phase concern favours keeping the capsules closer together.
Consider AB
A wide AB spaced pair would be very spacious but has the greatest comb-filtering and 'hole in the middle' risk, and worst mono compatibility.
Consider ORTF
ORTF (two cardioids 17 cm apart at 110 degrees) gives a realistic, spacious image using both time and level differences, while its modest spacing limits comb filtering and keeps mono reasonably safe.
Recommend
Because the release is stereo but the producer fears phase problems, ORTF is the better all-rounder - spacious and realistic yet mono-tolerant.

Result: Recommend ORTF: it delivers the wanted spacious, realistic image with far less phase risk than a wide AB pair.

Typical mistakes

Spacing microphones too far apart, creating a vague centre ('hole in the middle') and severe mono cancellation.
Forgetting ORTF's specific geometry - 17 cm capsule spacing and a 110-degree angle - which defines it.

Active revision

Compare an AB spaced pair and an ORTF pair for recording a string quartet that will be released in stereo only, and recommend one with reasons.

Active recall

Recall the key points — then reveal.

Sources: Pearson Edexcel Level 3 Advanced GCE in Music Technology (9MT0) Specification (Pearson Edexcel)

Mid-side (MS)#

AdvancedPearson 9MT0 - microphone placement techniques

The mid-side matrix decode

Fig. 4MS decode: the mid and side signals are matrixed to L = M + S and R = M - S. In mono, L + R = 2M, so the side cancels - perfect mono compatibility.

Mid-side (MS) is a coincident stereo technique with a unique advantage: adjustable width and perfect mono compatibility. It uses two coincident microphones - a mid microphone (usually a cardioid) pointing straight at the source, capturing the centre, and a side microphone (a figure-8) turned 90 degrees so its lobes face left and right, capturing the sides. Neither microphone alone is a stereo signal; the stereo image is created by matrixing the two together.

The decode is a simple sum and difference. The left channel is the mid plus the side (M + S); the right channel is the mid minus the side (M - S), where 'minus' means the side signal with its polarity inverted. A sound on the left is positive in the side microphone, so it adds into the left and subtracts from the right, appearing on the left; a sound on the right does the reverse; a central sound is in the mid only and appears equally in both. This matrix reconstructs a full left-right image from a forward and a sideways microphone.

The great strengths of MS follow from that matrix. First, the width is adjustable after recording: raising the level of the side signal relative to the mid widens the image, lowering it narrows toward mono - a control no other technique offers. Second, it is perfectly mono-compatible: summing left and right gives (M + S) + (M - S) = 2M, so the side cancels completely and the mono signal is exactly the mid microphone, with no comb filtering at all. This makes MS the safest possible stereo technique for broadcast.

MS is therefore favoured wherever mono compatibility is paramount or where the width may need adjusting later - broadcast, film, and any single-point stereo capture that must also fold down cleanly to mono. It does require a figure-8 microphone and the matrix decode (a dedicated plug-in, or three mixer channels: the mid, and the side panned hard left and its inverted copy panned hard right), but the flexibility and mono safety repay the small extra setup.

For the exam, be able to state the MS setup (coincident mid cardioid plus side figure-8), the decode (L = M + S, R = M - S), and its two headline benefits: post-recording width control and perfect mono compatibility (mono = 2M, side cancels). MS ties together polar patterns, phase and stereo imaging, and demonstrating the sum-and-difference reasoning clearly is a high-value answer.

Worked example

Proving mono compatibility of MS

Using the MS decode, show that an MS recording sums to mono with no side content, and explain the practical benefit.

Write the channels
The decode gives Left = M + S and Right = M - S.
Sum to mono
Mono is Left + Right = (M + S) + (M - S) = 2M; the +S and -S cancel exactly.
$(M + S) + (M - S) = 2M$
Interpret
The mono signal is purely the mid microphone (a clean cardioid capture), with the side completely gone - so there is no comb filtering or cancellation at all in mono.
Benefit
MS is the safest stereo technique for anything that may be heard in mono (broadcast, club systems), and its width can also be adjusted after the fact by changing the S level.

Result: L + R = 2M, so MS folds down to the pure mid signal in mono with no cancellation - the technique's defining advantage.

Typical mistakes

Forgetting that the right channel uses the side signal inverted (M - S), not a second side microphone.
Thinking MS needs two figure-8 microphones - it uses one mid (usually cardioid) and one side figure-8.

Active revision

Show, using L = M + S and R = M - S, that summing the two channels to mono cancels the side signal, and explain what practical advantage this gives.

Active recall

Recall the key points — then reveal.

Sources: Pearson Edexcel Level 3 Advanced GCE in Music Technology (9MT0) Specification (Pearson Edexcel)

Multi-mic setups, phase and spill#

AdvancedPearson 9MT0 - microphone placement techniques

The 3:1 rule on adjacent sources

Fig. 5The 3:1 rule: keep the distance between microphones at least three times each microphone's distance to its source, so spill arrives far quieter and comb filtering is negligible.

Large sources such as a drum kit or a piano are recorded with several microphones at once - close mics on individual elements plus overheads and room mics - and combining them raises the central problem of phase. When two microphones capture the same sound at slightly different distances, that sound arrives at them at slightly different times; when their signals are summed, the time difference causes some frequencies to reinforce and others to cancel, colouring the sound. Managing this is the core skill of multi-microphone recording.

The cancellation pattern is called comb filtering. Summing a sound with a delayed copy of itself produces a series of evenly spaced peaks and deep notches across the frequency spectrum - a shape like the teeth of a comb - because at some frequencies the two arrivals are in phase (reinforcing) and at others antiphase (cancelling). The notches fall at frequencies where the delay equals an odd number of half-periods. Even a small time difference of a fraction of a millisecond produces audible comb filtering, hollowing and phasing the sound.

The standard defence is the 3:1 rule. When using more than one microphone, the distance between any two microphones should be at least three times the distance from each microphone to its source. This ensures that the spill of one source into the other's microphone arrives at least about 9-12 dB quieter than the wanted source, so that when the channels are combined the comb filtering from the spill is too weak to be a problem. Following the 3:1 rule while placing multiple microphones is a routine, examinable discipline.

Spill (bleed) - unwanted sound from one source leaking into another's microphone - is the other multi-mic concern, and it is controlled by distance, by pointing polar-pattern nulls at the loudest neighbours, and by physical barriers or gobos. Some spill is inevitable and even desirable (it glues a kit together), but too much reduces control at the mix and causes the phase problems above. Checking the polarity of each microphone (and inverting any that is out of phase with the others) is part of getting a coherent multi-mic sound.

Planning a drum-kit setup shows all of this at once: close mics on the kick, snare and toms; a hi-hat mic angled so its null faces the snare; overheads placed to a consistent distance from the snare (so the snare is in phase in all mics) and obeying the 3:1 rule relative to the close mics; then a polarity check across the whole kit. For the exam, be able to plan such a setup and to explain, using comb filtering and the 3:1 rule, why the spacings are chosen and how phase problems are avoided.

Comb filtering from a delayed copy

Fig. 6Summing a sound with a delayed copy gives a comb filter: reinforcing peaks and cancelling notches at evenly spaced frequencies (here against f x delay).

Worked example

Planning a phase-safe drum setup

Plan the microphone placement for a kick, snare, hi-hat and a pair of overheads so that the kit combines without phase problems.

Close mics and the 3:1 rule
Place close mics near the kick and snare; keep each pair of microphones at least three times as far apart as each is from its own source, so spill arrives far quieter and comb filtering is negligible.
Use the nulls
Angle the hi-hat microphone (cardioid) so its rear null faces the snare, reducing snare bleed into the hat mic.
Match the overhead distances
Position the two overheads so each is the same distance from the snare (measure with a cable), so the snare arrives in phase in both overheads and in mono.
Polarity check
Solo pairs and combine them; if the kick or a tom thins out when its close mic is added to the overheads, invert that microphone's polarity to restore the low end.

Result: Obey the 3:1 rule, aim nulls at neighbours, match overhead-to-snare distances, and check polarity across the kit - the plan that avoids comb filtering and phase cancellation.

Typical mistakes

Placing two microphones close together on one source at unequal distances, causing severe comb filtering when summed.
Ignoring polarity - one out-of-phase microphone can hollow out the whole combined sound.

Active revision

Plan a microphone setup for a drum kit (kick, snare, hi-hat and overheads) that avoids phase problems, stating how the 3:1 rule and polar-pattern nulls are used.

Active recall

Recall the key points — then reveal.

Sources: Pearson Edexcel Level 3 Advanced GCE in Music Technology (9MT0) Specification (Pearson Edexcel) · Ofqual - GCE AS and A level qualifications (subject-level conditions and requirements) (Ofqual)

References & sources

Sources

Pearson Edexcel

Pearson Edexcel Level 3 Advanced GCE in Music Technology (9MT0) Specification

Ofqual

Ofqual - GCE AS and A level qualifications (subject-level conditions and requirements)

Microphone placement techniques

5 sections~20 min reading time3 competenciesLevel Foundation 1 · Standard 2 · Advanced 2

Microphone placement techniques

Key points

Placing one microphone for tone

Key points

Choosing XY for a mono-safe capture

Key points

AB or ORTF for a stereo-only release

Key points

Proving mono compatibility of MS

Key points

Planning a phase-safe drum setup

Sources

Microphone placement techniques

Key points

Placing one microphone for tone

Key points

Choosing XY for a mono-safe capture

Key points

AB or ORTF for a stereo-only release

Key points

Proving mono compatibility of MS

Key points

Planning a phase-safe drum setup

Sources