Sound Capture - Microphone frequency response

Learning Outcomes

• Explain what microphone frequency response means and how it is shown on a response curve.
• Interpret a simple microphone frequency response graph using frequency and dB axes.
• Compare the typical frequency response characteristics of dynamic, condenser and ribbon microphones.
• Choose suitable microphones for common recording sources based on tonal response.
• Identify how frequency response affects brightness, warmth, harshness, sibilance and detail.
• Describe how EQ can correct or use microphone frequency response creatively.
• Avoid common recording mistakes caused by relying only on microphone type or brand.

Edexcel A-Level Music Technology (9MT0) Syllabus

For Component 1: Recording, you are expected to make informed sound capture decisions, including selecting suitable microphones and placing them effectively. Microphone frequency response is part of that decision-making: different microphones do not capture all frequencies equally, so their tonal character affects the recorded sound before any EQ is applied.

• Understand that microphones can boost or reduce parts of the frequency spectrum.
• Recognise that a response curve shows frequency on the horizontal axis and level change in dB on the vertical axis.
• Link microphone choice to source: vocals, acoustic guitar, piano, drums, guitar amplifier, brass and ambience.
• Explain why condenser microphones often capture more high-frequency detail than dynamic microphones.
• Explain why dynamic microphones can sound warmer or less bright on some sources.
• Use frequency response knowledge to justify practical decisions in a recording logbook or written answer.
• Connect microphone response with later EQ choices, such as cutting harshness or adding presence.

Test Your Knowledge

Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision.

1. What does a microphone frequency response curve show?
2. Why might a dynamic microphone make an electric guitar amplifier sound warmer?
3. Why are condenser microphones often useful for acoustic instruments and ambient recording?
4. What frequency areas might affect vocal sibilance, presence and warmth?
5. How could you use EQ if a microphone has captured too much low-mid muddiness?

Introduction

Microphone choice is not only about polar pattern, price or whether the microphone is dynamic or condenser. Every microphone has a tonal character, and a major part of that character is its frequency response. This describes how evenly, or unevenly, the microphone captures low, middle and high frequencies.

In recording, frequency response matters because it shapes the sound at the capture stage. If you record a vocal with a bright condenser microphone, the performance may sound clear and detailed, but sibilance may become more obvious. If you record an electric guitar cabinet with a dynamic microphone that has less high-frequency extension, the result may feel warmer and less harsh. These decisions affect how much EQ you need later and how natural the final mix sounds.

Key Term: frequency response
The way a microphone, speaker or other audio device responds to different frequencies, often shown as boosts or cuts across the audible spectrum.

Reading a microphone frequency response curve

A microphone frequency response curve is a graph. The horizontal axis shows frequency, usually from low bass on the left to high treble on the right. The vertical axis shows level, normally in decibels, above or below a central 0 dB line. If the line rises above 0 dB at a certain frequency, that frequency range is captured more strongly. If it dips below 0 dB, that area is captured less strongly.

Key Term: frequency response curve
A graph showing how much a microphone boosts or reduces different frequencies compared with a reference level.

Most microphone response graphs use a logarithmic frequency scale, because human hearing perceives pitch in ratios rather than equal steps of hertz. This means the spacing between 100 Hz and 200 Hz may look similar to the spacing between 1 kHz and 2 kHz, even though the second gap contains many more hertz. For exam work, you do not need to become a graph specialist, but you must be able to identify broad trends.

For example, a curve might show:

• a gentle roll-off below 80 Hz, meaning less sub-bass and less rumble;
• a rise around 3–5 kHz, giving more presence or clarity;
• a peak around 8–10 kHz, adding brightness or “air” but possibly increasing sibilance;
• a dip around 300–500 Hz, reducing boxiness or low-mid thickness.

The central 0 dB line does not mean “silence”. It means the reference level for comparison. A microphone that is +4 dB at 5 kHz will capture that area more strongly than a microphone that is flat at 5 kHz, assuming the same source and placement.

Key Term: decibel (dB)
A unit used to compare levels. On a frequency response graph, dB values show how much louder or quieter a frequency range is relative to a reference level.

A perfectly flat response would be shown as a straight line at 0 dB across the whole frequency range. In practice, many microphones are not completely flat. This is not always a fault. A vocal microphone may deliberately have a presence boost to help a voice cut through a mix. A kick drum microphone may have a shaped response with enhanced low end and attack. A measurement microphone, by contrast, is designed to be as flat as possible so that it can analyse sound without adding much tonal colour.

Test Tip: If you are asked to interpret a frequency response graph, describe both the frequency area and the effect on the sound. For example: “A boost around 5 kHz may increase presence and make vocals more forward,” rather than only writing “there is a boost.”

Flat, coloured and shaped responses

A microphone with a flat frequency response captures frequencies with relatively little tonal alteration. Condenser microphones are often associated with a flatter response than many dynamic microphones, partly because their lighter diaphragm can move more easily. This helps them capture detail, especially high-frequency detail and fast transients.

Key Term: flat frequency response
A response in which low, mid and high frequencies are captured at similar levels, with little tonal emphasis or reduction.

Flat response is useful when you want an accurate capture of the source. For example, a small-diaphragm condenser on acoustic guitar can capture the brightness of the strings, the detail of finger movement and the natural tone of the instrument. A pair of condensers used as drum overheads can capture cymbals, stereo image and the overall kit sound. A condenser placed for ambience can capture the sound of the room without strong tonal colour from the microphone itself.

However, a flat response is not always the best artistic choice. A microphone with a coloured response can help a source sit in a mix. For instance, an electric guitar amplifier may produce a sharp or fizzy top end. A dynamic microphone with a less extended high-frequency response can reduce that edge before the signal reaches the DAW. This can make the recording sound warmer and reduce the need for later EQ cuts.

Key Term: coloured response
A frequency response that changes the tone of the source by emphasising or reducing particular frequency areas.

The word “coloured” does not automatically mean bad. Colour can be useful. Many classic microphone choices are valued because they flatter particular sources. A vocal microphone with a smooth high-frequency lift can add clarity. A bass drum microphone with a low-frequency lift can add weight. A microphone with a low-mid dip can reduce muddiness.

The main exam skill is to link the response to the likely sound. Avoid vague descriptions such as “better quality”. Instead, use cause and effect:

• A high-frequency lift may make a recording brighter, clearer or more detailed.
• A weak high-frequency response may make a sound duller, warmer or less harsh.
• A low-frequency roll-off may reduce rumble or make the sound thinner.
• A low-mid boost may add body, but too much can sound muddy or boxy.
• A presence boost in the upper mids can help vocals, snare or guitar cut through.

Exam Warning: Do not assume that “flat” always means “best”. In a recording task, the best microphone is the one that suits the source, performance style, room, mix context and intended sound.

Microphone types and their typical tonal behaviour

Dynamic microphones are often used for loud sources such as drums, guitar amplifiers, bass amplifiers and some brass instruments. They can handle high sound pressure levels and are physically tough. Their main drawback is that they are usually less sensitive than condenser microphones, and their high-frequency response is often less detailed.

Key Term: dynamic microphone
A microphone type that uses electromagnetic induction, is generally durable, handles loud sources well and usually needs no external power.

This limited high-frequency response can be useful. On an electric guitar amplifier, a dynamic microphone can reduce harsh upper harmonics and give a warmer recorded tone. On snare drum, it can capture strong midrange impact without making every cymbal spill painfully bright. On live vocals, a dynamic microphone can help control spill and withstand close use.

Condenser microphones are common in studio recording. They usually require phantom power or a battery, and they are more sensitive than dynamic microphones. Because of this sensitivity and their often flatter frequency response, they can capture quieter sounds and more detail.

Key Term: condenser microphone
A microphone type that uses a charged capacitor system, usually needs phantom power or a battery, and is often sensitive with extended high-frequency detail.

Condenser microphones are well suited to vocals, acoustic guitar, piano, orchestral instruments, drum overheads, small percussion and ambient recording. A large-diaphragm condenser may flatter a vocal by adding detail and presence. A small-diaphragm condenser may capture fast transients and high-frequency information accurately, making it useful on acoustic guitar, hi-hat, cymbals or stereo piano techniques.

There are also disadvantages. Because condensers are sensitive, they may capture unwanted room sound, headphone spill, mouth noise or harshness if used carelessly. They may overload on very loud sources if placed too close, although many have a pad switch to reduce level before the microphone electronics distort. Moisture can also be a concern with singers and brass instruments, so a pop shield and careful placement are sensible.

Ribbon microphones are also relevant when discussing frequency response, although you may use them less often in a school or college recording setup. Traditional ribbon microphones often have a smooth high-frequency response rather than a bright, hyped top end. This can make them useful for taming harsh brass, guitar amplifiers or bright strings. Many ribbon microphones use a figure-of-eight polar pattern, so room sound and rear pickup must be considered carefully.

Key Term: ribbon microphone
A microphone type using a thin metal ribbon as the transducer element, often associated with a smooth high-frequency response and figure-of-eight pickup.

Test Tip: In a written answer, name a microphone type and justify it using frequency response. Example: “I would use a condenser on acoustic guitar because its extended high-frequency response would capture string detail and brightness.”

Frequency response in practical recording decisions

Frequency response becomes useful when you connect it to a real source. In Component 1, this means making choices that improve the captured sound before mixing. Good capture reduces the need for heavy processing later.

For vocals, a condenser microphone is often a good starting point because it captures detail, breath and articulation. A gentle boost in the upper mids can help the vocal sit forward. However, too much energy around the sibilance range can make “s”, “sh” and “t” sounds too sharp. If the singer is already bright or sibilant, a smoother microphone, a different angle, a pop shield or a small EQ cut may be better than simply accepting the harshness.

Key Term: sibilance
Strong high-frequency vocal sounds produced by consonants such as “s”, “sh” and “t”, often most noticeable in the upper treble range.

For acoustic guitar, frequency response affects whether the result sounds natural, boomy, thin or bright. A condenser pointed near the 12th fret often captures a balance of string brightness and body. If the microphone or position captures too much low-mid energy, the guitar may sound muddy. If it captures too much high end, pick noise may become distracting. Moving the microphone can change the balance as much as choosing another microphone.

For piano, a microphone with a fairly even response helps capture the wide pitch range of the instrument. A piano includes bass fundamentals, midrange body and bright hammer attack. A pair of condensers can capture this range well, but placement controls the tonal result: closer to the hammers gives more attack and brightness; further away gives more room sound and blend.

For drums, different parts of the kit often benefit from different responses. A dynamic microphone on snare can handle loud transients and give a strong midrange crack. A kick drum microphone may be chosen for low-end weight and beater attack. Condenser overheads capture cymbals and the full kit image, so their high-frequency response matters greatly. A very bright overhead pair can make cymbals sound harsh, while a dull pair can make the kit lack sparkle.

For electric guitar amplifiers, a dynamic microphone close to the speaker is a standard choice because it can handle loud sound pressure levels and may reduce harsh high frequencies. Placement across the speaker cone also changes the tone: the centre is usually brighter and more direct, while the edge is often darker. This means microphone placement and frequency response work together.

Key Term: transient response
How quickly a microphone reacts to sudden changes in sound level, such as drum hits, plucked strings or consonants.

Frequency response is also affected by distance and direction. Directional microphones may show a proximity effect: when used very close to the source, low frequencies are boosted. This can make a vocal sound warm and intimate, but it can also make it boomy. Off-axis sound may also be less accurate than on-axis sound. A microphone might have a smooth response from the front but colour spill from the sides. This matters when recording ensembles, drum kits or loud rooms.

Key Term: proximity effect
The increase in low-frequency response that occurs when some directional microphones are placed very close to a sound source.

Exam Warning: Do not describe microphone tone as if it comes only from the microphone model. The final captured frequency balance also depends on source, room, polar pattern, distance, angle, performer technique and input level.

Using EQ to correct or enhance microphone response

Equalisation can adjust tonal problems after capture, but it is better to start with a suitable microphone and placement. EQ was originally used to compensate for tonal weaknesses in audio systems, but in modern production it is also a creative tool. In recording work, EQ can either correct a frequency response issue or shape the sound for the mix.

Key Term: equalisation (EQ)
The process of boosting or cutting selected frequency areas to alter the tonal balance of an audio signal.

If a microphone captures too much low-frequency rumble, a high-pass filter can remove unnecessary sub-bass. This is common on vocals, acoustic guitar and overheads, where very low frequencies may not be musically useful. If a vocal sounds muddy, a gentle cut in the low mids may help. If it lacks clarity, a small upper-mid or high-frequency boost may bring it forward.

If a recording has a narrow ringing tone, room node or hum, a narrow EQ cut may be used. A notch filter is designed for this kind of task because it cuts a very small frequency area. This is different from making broad tonal changes.

Key Term: notch filter
A very narrow EQ cut used to reduce a specific frequency, such as hum, ringing or a room resonance.

A frequency response curve can help you make these decisions. If a microphone has a strong presence peak and the recorded vocal sounds aggressive, you might reduce a similar upper-mid area with EQ. If an acoustic guitar sounds thin and the microphone response falls away in the low mids, you might use a different microphone or add a careful EQ boost. But EQ is not magic: if the microphone failed to capture detail clearly, boosting high frequencies may only bring up hiss, spill or harshness.

When writing about EQ in an exam or logbook, be precise. “I used EQ to make it sound better” is weak. Better answers explain the frequency area, process and reason:

• “I applied a high-pass filter to the vocal to reduce low-frequency rumble.”
• “I cut around the low-mid range to reduce muddiness in the acoustic guitar.”
• “I used a small high-frequency boost to add brightness to the overheads.”
• “I used a narrow cut to reduce a ringing resonance.”

Test Tip: In Component 1 documentation, link microphone response to later processing. For example: “The condenser captured the detail I wanted, but I used a de-esser because the bright response made sibilance more noticeable.”

Key Point Checklist

This article has covered the following key knowledge points:

• Microphone frequency response describes how a microphone captures different frequencies.
• A response curve shows frequency on the horizontal axis and level change in dB on the vertical axis.
• A flat frequency response means the microphone captures frequencies with little tonal emphasis.
• Condenser microphones are often sensitive, detailed and suited to vocals, acoustic instruments, piano, overheads and ambience.
• Dynamic microphones often handle loud sources well and may have a less extended high-frequency response.
• A limited high-frequency response can make electric guitar amplifiers or loud sources sound warmer and less harsh.
• Ribbon microphones are often associated with smooth high frequencies and can suit harsh or bright sources.
• Frequency response affects practical descriptions such as bright, dull, warm, muddy, boxy, clear, harsh and present.
• Proximity effect can increase low frequencies when directional microphones are used close to the source.
• EQ can correct or enhance captured tone, but good microphone choice and placement should come first.
• A notch filter can reduce a narrow unwanted frequency such as hum, ringing or a room resonance.
• Strong exam answers link microphone choice, frequency response and audible result.

Key Terms and Concepts

• frequency response
• frequency response curve
• decibel (dB)
• flat frequency response
• coloured response
• dynamic microphone
• condenser microphone
• ribbon microphone
• sibilance
• transient response
• proximity effect
• equalisation (EQ)
• notch filter