Notes · Music TechnologyUK · A-Levels

Microphones and capture of sound

The microphone is the studio's ear: it converts sound pressure into the voltage the whole chain will process, so its type, directionality and response colour everything that follows. This topic covers the three transducer types and their trade-offs, the polar patterns that set what a microphone hears and rejects, its frequency and transient response, the proximity effect of directional microphones, and the gain structure and phantom power that get a clean signal into the recorder.

5 sections~19 min reading time3 competenciesLevel Foundation 1 · Standard 3 · Advanced 1

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Exam profile

C1 · Select microphone type and polar pattern to suit a source and capture it cleanlyC3 · Relate microphone frequency and transient response and the proximity effect to the recorded soundC1 · Set gain structure and phantom power correctly at the point of capture

Operators:describeexplainselectjustifycalculate

basic level

The AS foundation is the three microphone types, the common polar patterns, and phantom power.

higher level

The full A-level adds frequency/transient response, the proximity effect and gain-structure reasoning for capture.

Depth

Text

Contents · 5 sections

Microphones and capture of sound

How microphones work: transducer types#

FoundationPearson 9MT0 - microphones and capture of sound

Microphone transducer types

Fig. 1The three transducer types and their trade-offs: dynamics are rugged and handle loud sources; condensers are sensitive and detailed but need phantom power; ribbons are warm and delicate.

A microphone is a transducer that converts the pressure variations of sound into an electrical voltage, and there are three main ways of doing this, each with a characteristic sound and set of practical trade-offs. Choosing the right type for a source is the first capture decision, and it is guided by the source's loudness, its transient content and the sound you want.

The dynamic (moving-coil) microphone works by electromagnetic induction: the sound moves a diaphragm attached to a coil of wire suspended in a magnetic field, and the coil's motion generates a voltage. Dynamics are rugged, need no power, handle very high sound-pressure levels without distorting and are relatively insensitive to quiet detail, which makes them the standard choice for loud, close sources - drums, guitar amplifiers, live vocals - and for hostile environments.

The condenser (capacitor) microphone uses a thin, charged diaphragm forming one plate of a capacitor; as sound moves the diaphragm, the capacitance changes and produces a voltage. Condensers are far more sensitive and have a faster, more detailed response, capturing transients and high-frequency air that dynamics miss, which makes them the studio choice for vocals, acoustic instruments and overheads. The catch is that they need power - phantom power (+48V) - to charge the capsule and run their internal electronics, and they are more fragile and less tolerant of extreme levels.

The ribbon microphone is a specialised dynamic type in which a thin corrugated metal ribbon suspended in a magnetic field acts as both diaphragm and conductor. Ribbons have a smooth, warm, slightly rolled-off top end and a naturally figure-8 pattern, and are prized on brass, strings and guitar amps. They are delicate - fragile to wind blasts and, crucially, to phantom power, which can destroy some ribbons - so they must be handled and patched with care.

The practical upshot is a small decision tree: for a loud, robust source that does not need fine detail, reach for a dynamic; for a quiet or detailed source where transients and high-frequency air matter, use a condenser and switch on phantom power; for a warm, smooth capture of brass or strings, consider a ribbon, and never send it phantom power. This choice, made before a note is recorded, shapes the character of everything downstream.

Worked example

Matching microphone to source

A session needs to capture a loud electric guitar cabinet and, separately, a soft, detailed classical guitar. Choose a microphone type for each and justify it.

The loud cabinet
A guitar amp produces very high sound-pressure levels; a dynamic (moving-coil) microphone handles the level, is rugged, and gives a focused sound without needing power.
The classical guitar
A quiet, transient-rich acoustic needs sensitivity and high-frequency detail, so a condenser microphone with phantom power captures the string detail and air.
Confirm phantom
Switch phantom power on for the condenser; the dynamic ignores it, so a shared phantom bus is safe here (no ribbons involved).

Result: Use a dynamic on the loud cabinet and a phantom-powered condenser on the classical guitar - level-handling versus detail.

Typical mistakes

Saying a dynamic microphone needs phantom power - it does not; only condensers (and active DIs) do.
Sending phantom power to a ribbon microphone, which can destroy the ribbon.

Active revision

Choose a microphone type for (a) a loud snare drum, (b) a delicate fingerpicked acoustic guitar, and (c) a warm trumpet line, and justify each choice.

Active recall

Recall the key points — then reveal.

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

Polar patterns#

StandardPearson 9MT0 - microphones and capture of sound

The four polar patterns

Fig. 2The polar patterns by what they accept and reject - the key to isolating a source and aiming a null at spill.

A microphone's polar pattern (directional response) describes how its sensitivity varies with the direction a sound comes from - what it hears and what it rejects. Choosing the pattern controls how much of the wanted source, the room and other instruments (spill) is captured, and it is as important as the microphone type. The patterns are shown on a polar plot, but the practical facts are which directions each accepts and rejects.

The omnidirectional pattern is equally sensitive in all directions. It captures the most natural, open sound and the fullest low frequencies, has no proximity effect and handles wind well, but it rejects nothing - it picks up the whole room and any spill. Omnis suit capturing an ensemble or a room deliberately, or close work where isolation is not needed.

The cardioid pattern (heart-shaped) is most sensitive at the front and progressively rejects the rear, with a deep null directly behind. It is the workhorse pattern: pointing it at a source and its null at an unwanted sound isolates the source and rejects spill and feedback, which is why cardioids dominate close miking and live use. Its variants tighten the front lobe at the cost of a small rear pickup: the hypercardioid has an even narrower front but a small rear lobe and its nulls at the sides-rear, giving the greatest side rejection.

The figure-8 (bidirectional) pattern is equally sensitive front and rear but rejects the sides completely, with deep nulls at 90 degrees. It is the natural pattern of ribbon microphones and is essential to mid-side stereo and to techniques that exploit its side rejection - for example placing the nulls toward an instrument you want to exclude. Understanding where each pattern's nulls point is the key to using it: you aim the null at what you want to reject, not just the front at what you want.

Many condenser microphones are multi-pattern, switching between omni, cardioid and figure-8 (and intermediates), so pattern becomes a creative and corrective control. The practical reasoning is always the same: decide what you want to capture and, just as importantly, what you want to reject, then choose the pattern whose sensitive lobe faces the source and whose null faces the problem. Pattern choice, distance and axis together determine the balance of direct sound, room and spill in the recording.

Using a cardioid null to reject spill

Fig. 3A cardioid points its sensitive front at the wanted source and its rear null at the spill, capturing the source while rejecting the unwanted sound behind.

Worked example

Aiming a null at spill

A backing vocalist stands close to a drum kit that is bleeding into her microphone. Choose a pattern and orientation to reduce the drum spill.

Identify the problem direction
The unwanted sound (the drums) comes from a definite direction, so the aim is to point a null at the kit.
Choose the pattern
A cardioid or hypercardioid gives strong rear (and, for the hyper, sides-rear) rejection; a cardioid's deep rear null is ideal if the kit is behind the singer.
Orient it
Point the front of the microphone at the singer's mouth and rotate the whole microphone so its rear null faces the drum kit.
Confirm
Solo the microphone: the vocal stays present while the drum bleed drops noticeably, because the kit now sits in the pattern's null.

Result: Use a cardioid (or hypercardioid), front to the singer and rear null aimed at the kit, so the null - not just the front - does the rejecting.

Typical mistakes

Thinking a cardioid rejects sound from the sides most - its deepest null is at the rear; the hypercardioid rejects the sides-rear.
Forgetting that an omni has no rejection at all, so it captures the whole room and any spill.

Active revision

A singer is next to a noisy amplifier. State which polar pattern you would choose and how you would orient the microphone to reject the amp while capturing the voice.

Active recall

Recall the key points — then reveal.

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

Frequency and transient response#

StandardPearson 9MT0 - microphones and capture of sound

Flat versus presence-peaked microphone response

Fig. 4A flat response (reference) reproduces all frequencies equally; a vocal microphone's presence peak lifts the upper-mids around 5 kHz to add intelligibility and air.

A microphone's frequency response is the graph of its sensitivity against frequency, and it is a major part of its character. A flat response reproduces all frequencies equally and is the ideal for a measurement or a neutral capture; but many microphones are deliberately tailored - a gentle low-frequency roll-off to reduce rumble, or a broad boost in the upper-mid 'presence' region (around 3-8 kHz) to add intelligibility and 'air' to vocals. Reading a microphone's response curve tells you the tonal colour it will impose before any EQ.

The presence peak is the most common tailoring: a rise of a few decibels around 5 kHz helps a voice cut through a mix and adds articulation to consonants, which is why so many vocal microphones have one built in. It is effectively EQ applied acoustically at the capsule, and choosing a microphone with the right response can do work that would otherwise need EQ later - or create a problem (excess sibilance) that later processing must undo.

Transient response describes how quickly and accurately a microphone follows sudden changes - the sharp attack of a snare hit, a plucked string, a consonant. Condensers, with their light diaphragms, have a fast transient response and capture attacks crisply; dynamics, with heavier moving parts, are slower and slightly soften transients, which can be flattering on some sources and limiting on others. Matching transient response to the source (a fast condenser on a detailed acoustic, a dynamic to tame an aggressive one) is a real capture decision.

Sensitivity is a related specification: how much voltage the microphone produces for a given sound pressure. A sensitive microphone (typically a condenser) produces a strong signal from a quiet source, easing the demand on the pre-amp and improving the signal-to-noise ratio; an insensitive one (a dynamic) needs more pre-amp gain, which is fine on loud sources but can raise noise on quiet ones. Sensitivity, frequency response and transient response together explain why two microphones on the same source sound different.

For the exam, be able to read a response curve - identifying a flat region, a low roll-off and a presence peak - and to reason about how it and the transient response will colour a source. The key idea is that the microphone is the first tonal decision: its response is baked into the recording, so choosing it well can save corrective work later, and choosing it badly leaves problems that EQ can only partly fix.

Worked example

Choosing a response for a source

Two microphones are offered for a lead vocal: one flat, one with a broad +5 dB presence peak around 5 kHz. The singer already sounds slightly dull in the mix. Which is the better choice and why?

Diagnose the need
A dull vocal lacks upper-mid articulation and air, exactly the region a presence peak boosts.
Match the response
The presence-peaked microphone lifts around 5 kHz, adding intelligibility and helping the voice cut through, addressing the dullness at the capsule.
Consider the risk
If the singer were already sibilant, the presence peak could exaggerate 's' sounds and need de-essing; here dullness is the problem, so the peak helps.
Conclude
Choose the presence-peaked microphone, saving corrective EQ, but monitor sibilance.

Result: The presence-peaked microphone suits the dull vocal, lifting the 5 kHz region acoustically so less corrective EQ is needed - provided sibilance stays controlled.

Typical mistakes

Assuming every microphone is flat - most are tailored, and a presence peak or roll-off colours the sound before any EQ.
Confusing sensitivity (output per sound pressure) with the maximum level a microphone can handle.

Active revision

Sketch or describe the frequency response you would want in a vocal microphone and explain how a presence peak helps a voice sit in a mix.

Active recall

Recall the key points — then reveal.

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

The proximity effect and working distance#

StandardPearson 9MT0 - microphones and capture of sound

Proximity bass boost with distance

Fig. 5Close to a directional microphone, low frequencies are boosted (the proximity effect); at a distance the response is flat. The boost grows as the microphone gets closer.

The proximity effect is the boost in low frequencies that directional microphones (cardioid, hypercardioid, figure-8) produce as they are moved close to a source. Within a few centimetres the bass rises substantially - several decibels - giving the warm, intimate, chesty sound of a close-miked voice or the fullness of a close-miked kick drum. Omnidirectional microphones do not exhibit it, because it arises from the way directional patterns sense the pressure gradient across the capsule, which strengthens at close range.

The effect is a tool and a trap. Used deliberately, it adds warmth and body - radio presenters and singers 'work the microphone', moving closer for intimacy and further back for a leaner sound. Left unmanaged, it makes close vocals boomy and muddy and exaggerates plosives, needing a high-pass filter or EQ cut to tame. Knowing that moving closer adds bass, and moving back removes it, gives dynamic control of tone by distance alone.

Working distance also sets the balance of direct to reflected sound and the level. Close miking captures mostly direct sound with little room, giving isolation and a big, present tone (with proximity bass); distant miking captures more room and a more natural, distant perspective, at a lower level. By the inverse-square law, doubling the distance drops the level by about 6 dB and roughly doubles the proportion of room sound, so distance trades presence and isolation against natural ambience.

The two effects combine in practice. A vocalist a few centimetres away is loud, isolated, present and warm (strong proximity bass); the same vocalist half a metre back is quieter, airier, more roomy and leaner. The recordist chooses the working distance to get the wanted balance of tone, level, isolation and room, and then fine-tunes with pattern and EQ. This is why microphone distance is described as one of the most powerful tonal controls available before any processing.

For the exam, be able to state that directional microphones show a proximity bass boost that increases as distance decreases (and that omnis do not), and to reason about the trade-offs of working distance: close for isolation, presence and proximity warmth; distant for a natural, roomier, quieter sound. Managing the proximity effect - exploiting it or filtering it out - is a routine capture decision.

Worked example

Working the microphone for tone

A singer with a cardioid microphone wants a warm, intimate sound on the verses and a leaner, brighter sound on the loud choruses. Explain how distance achieves this and one issue to watch.

Verses - move in
Singing a few centimetres from the cardioid engages the proximity effect, boosting the low frequencies for a warm, intimate tone, and raising the level.
Choruses - back off
Moving back reduces the proximity bass for a leaner sound and lowers the level, helpfully controlling the loud passages by the inverse-square law.
The issue
Close working exaggerates plosives and boominess, so a pop shield and a high-pass filter guard against 'p'/'b' pops and excess low end.
Result
Distance alone shapes both tone and level, with the pop shield and high-pass keeping the close position clean.

Result: Move in for warm, louder verses (proximity bass) and back off for lean, quieter choruses; guard the close position with a pop shield and high-pass filter.

Typical mistakes

Attributing the proximity effect to all microphones - omnidirectional microphones do not exhibit it.
Ignoring plosives and boom when close-miking a directional microphone without a high-pass filter or pop shield.

Active revision

Explain how a singer can vary the warmth of their tone using distance alone with a cardioid microphone, and state one problem close working can cause.

Active recall

Recall the key points — then reveal.

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

Gain structure and phantom power at capture#

AdvancedPearson 9MT0 - microphones and capture of sound

Gain structure and self-noise at capture

Fig. 6At capture the pre-amp gain lifts the signal above the microphone and pre-amp self-noise, fixing the signal-to-noise ratio; a pad protects loud sources and +48V powers a condenser.

Once the microphone and pattern are chosen, capturing a clean signal is a matter of gain structure and self-noise. Every microphone and pre-amp adds a little noise, and the signal-to-noise ratio of the recording is fixed at the front end: the pre-amp gain must lift the microphone's output well above the noise floor without pushing the loudest peaks into clipping. This early setting cannot be repaired later, because raising a too-quiet recording afterwards raises its noise with it.

Self-noise matters most on quiet sources. A condenser's own electronic noise (quoted as an equivalent noise level) becomes audible when capturing a soft, distant sound that needs a lot of gain, so quiet sources favour sensitive, low-self-noise condensers and generous but clean pre-amp gain. On loud sources the opposite problem dominates - too much level - and the answer is a pad and a robust microphone rather than more gain.

Phantom power (+48V) is supplied up the balanced cable to run condenser microphones and active DI boxes. It must be switched on for condensers and, as noted, kept away from ribbons. It is applied equally to both signal conductors of the balanced pair, so it does not appear across the audio and is invisible to dynamic microphones, which is why a mixed setup of dynamics and condensers can share a phantom bus safely - provided no ribbons are patched.

The pad and the high-pass filter are the two front-end tools that protect the capture. A pad attenuates the signal (typically by 10-20 dB) before the pre-amp so a very loud source does not overload the input even at minimum gain; a high-pass filter removes subsonic rumble, stand vibration and some proximity boom at source, keeping that energy out of the whole chain. Both are set at the point of capture, before conversion.

The disciplined capture routine ties this together: choose the microphone and pattern; enable phantom (for a condenser) or fit a DI; engage a pad if the source is very loud; add a high-pass if rumble is present; then raise the pre-amp gain while the performer plays their loudest passage until peaks sit with headroom (around -12 to -6 dBFS). Because this sets the signal-to-noise ratio for everything downstream, it is the most consequential adjustment in the whole recording, and examiners reward candidates who describe it as a deliberate, ordered process.

Worked example

Capturing a quiet source cleanly

A soft acoustic guitar harmonic passage must be recorded with a condenser microphone but the take is noisy when turned up. Diagnose and fix the gain structure.

Identify the cause
The quiet source was recorded with too little pre-amp gain, so it sits close to the noise floor; boosting it in the mix raised the noise too.
Enable phantom
Confirm +48V is on for the condenser so it operates and delivers its full, sensitive output.
Set gain for headroom
Raise the pre-amp gain during the loudest part of the passage until peaks reach about -8 to -6 dBFS, lifting the signal well above the noise floor and fixing a good signal-to-noise ratio.
Do not pad
Because the source is quiet, do not engage a pad; a pad would only force even more gain and more noise.

Result: The noise came from too little gain at capture; enabling phantom and raising the pre-amp gain for headroom fixes the signal-to-noise ratio at source, where it must be set.

Typical mistakes

Recording too quietly and boosting later, which raises the noise floor along with the signal.
Overloading the input on a loud source instead of engaging a pad to regain gain range.

Active revision

Write, in order, the front-end steps to capture a quiet solo flute cleanly with a condenser microphone, explaining the purpose of each.

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)

Microphones and capture of sound

5 sections~19 min reading time3 competenciesLevel Foundation 1 · Standard 3 · Advanced 1

Microphones and capture of sound

Key points

Matching microphone to source

Key points

Aiming a null at spill

Key points

Choosing a response for a source

Key points

Working the microphone for tone

Key points

Capturing a quiet source cleanly

Sources

Microphones and capture of sound

Key points

Matching microphone to source

Key points

Aiming a null at spill

Key points

Choosing a response for a source

Key points

Working the microphone for tone

Key points

Capturing a quiet source cleanly

Sources