Microphone practice

Last updated December 11, 2024

There are a number of well-developed microphone techniques used for recording musical, film, or voice sources or picking up sounds as part of sound reinforcement systems. The choice of technique depends on a number of factors, including:

The wish to capture or avoid the collection of extraneous noise. This can be a concern, especially in amplified performances, where audio feedback can be a significant problem. Alternatively, it can be a desired outcome, in situations where ambient noise is useful such as capturing hall reverberation and audience reactions in a live recording.
Degree of directionality of pickup: in some settings, such as a home video of a birthday party, the person may wish to pick up all the sounds in the room, making an omnidirectional mic desirable. However, if a TV news crew is filming a reporter at a noisy protest, they may only wish to pick up her voice, making a cardioid mic more desirable.
Choice of a signal type: Mono, stereo or multi-channel.
Type of sound source: Acoustic instruments produce a sound very different from amplified electric instruments, which are again different from the human voice.
Sound pressure levels: a mic that is recording Baroque lute will not face high sound pressure levels, which could lead to distortion; on the other hand, a mic being used to record heavy metal drumming or brass instrument may face extreme sound pressure levels.
Situational circumstances: Sometimes a microphone should not be visible, or having a microphone nearby is not appropriate. In scenes for a movie the microphone may be held above, out of the picture frame.
Processing: If the signal is destined to be heavily processed, or mixed down, a different type of input may be required.
The use of a windscreen for outdoor recording or a pop shield to reduce vocal plosives.

Basic techniques

There are several classes of microphone placement for recording and amplification.

In close miking, a microphone is placed relatively close to an instrument or sound source, within three to twelve inches, producing a dry or non-reverberant sound.^[1] This serves to reduce extraneous noise, including room reverberation and is commonly used when attempting to record a number of separate instruments while keeping the signals separate, or when trying to avoid feedback in an amplified performance. Close miking often affects the frequency response of the microphone, especially for directional mics that exhibit bass boost from the proximity effect. Ubiquitous in the tracking of instruments used in pop and popular music, examples of close-mic vocal tracks include many songs on Elliott Smith's Elliott Smith and Either/Or , Lily Allen's "The Fear", the chorus of Fergie's "Glamorous", Imogen Heap's lead on "Hide and Seek", and Madonna's spoken verses on "Erotica".^[2]
In ambient or distant miking, a microphone — typically a sensitive one — is placed at some distance from the sound source. The goal of this technique is to get a broader, natural mix of the sound source or sources, along with ambient sound, including reverberation from the room or hall. Example include The Jesus and Mary Chain's Psychocandy (excepting the vocals), Robert Plant's vocals on songs from Physical Graffiti , Tom Waits's lead vocals on his junkyard records, and Mick Jagger's lead-vocals on songs from Exile On Main Street .^[3]
In room miking a distant mic, referred to as the room mic, is used in conjunction with a close mic, "typically placed far enough past the critical distance in a room that the room's ambience and reverberations transduce at an equivalent, if not greater, volume than the sound source itself."^[4] Ubiquitous in pop, it is the industry standard for tracking rhythm guitars in rock. A celebrated example is the rhythm guitar on Led Zeppelin's "Communication Breakdown"^[4] while other examples include John Frusciante's electric guitar parts on BloodSugarSexMagik , Noel Gallagher's lead-guitar on "Champagne Supernova", and Billy Corgan's guitar on "Cherub Rock", "Today", "Bullet With Butterfly Wings", "Zero", and "Fuck You (An Ode to No One)".^[5]
Accent (or spot) microphone placement. Often, the tonal and ambient qualities will sound very different between a distant- and close-miked pickup. Under certain circumstances, it's difficult to obtain a naturally recorded balance when mixing the two together. For example, if a solo instrument within an orchestra needs an extra mic for added volume and presence, placing the mic too close would result in a pickup that sounds overly present, unnatural and out of context with the distant, overall orchestral pickup. To avoid this pitfall, a compromise in distance should be struck. A microphone that has been placed within a reasonably close range to an instrument or section within a larger ensemble (but not so close as to have an unnatural sound) is known as an accent (or spot) pickup . Whenever accent miking is used, care should be exercised in placement and pickup choices. The amount of accent signal that's introduced into the mix should sound natural relative to the overall pickup, and a good accent mic should only add presence to a solo passage and not stick out as separate, identifiable pickup.^[6]^[7]^[8]
Instrumental use of microphones has been developed by many experimental composers, musicians and sound artists. They use microphones in unconventional ways, for example by preparing them with objects, moving them around or using contact microphones to colour the sound and be able to amplify otherwise very silent sounds. Karlheinz Stockhausen used microphone movements by musicians in Mikrophonie I to discover the diverse sounds of a big tam-tam^[9] and Pauline Oliveros amplified apple boxes with contact microphones.^[10]

When using multiple microphones, respecting a 3-to-1 rule and placing microphones at least three times further from each other than they are from the source they are being used to pick up avoids cancellation and phase issues such as comb filtering when the microphone signals are mixed together.^[11]

Other techniques

A parabolic microphone used to capture sounds on the field during a football game. ParabolicMicrophone.jpg — A parabolic microphone used to capture sounds on the field during a football game.

Parabolic microphones are used to capture sounds on the field during football games. The parabolic dish has been compared metaphorically to a telephoto lens, in the way that it can focus the capture of sound.^[12]

Multi-track recording

Often each instrument or vocalist is miked separately, with one or more microphones recording to separate channels (tracks). At a later stage, the channels are combined ('mixed-down') to two channels for stereo or more for surround sound. The artists need not perform in the same place at the same time, and individual tracks (or sections of tracks) can be re-recorded to correct errors. Generally effects such as reverberation are added to each recorded channel, and different levels sent to left and right final channels to position the artist in the stereo sound-stage. Microphones may also be used to record the overall effect, or just the effect of the performance room.

This permits greater control over the final sound, but recording two channels (stereo recording) is simpler and cheaper, and can give a sound that is more natural.

Stereo recording techniques

There are two features of sound that the human brain uses to place objects in the stereo sound-field between the loudspeakers. These are the relative level (or loudness) difference between the two channels Δ L, and the time delay difference in arrival times for the same sound in each channel Δ t. The interaural signals (binaural ILD and ITD) at the ears are not the stereo microphone signals which are coming from the loudspeakers, and are called interchannel signals (Δ L and Δ t). These signals are normally not mixed. Loudspeaker signals are different from the sound arriving at the ear. See also Binaural recording.

There are several established microphone configurations used in ambient or room stereo recording.

X-Y technique

Here there are two directional microphones at the same place, and typically placed at 90° or more to each other.^[13] A stereo effect is achieved through differences in sound pressure level between two microphones. Due to the lack of differences in time-of-arrival and phase ambiguities, the sonic characteristic of X-Y recordings is generally less spacey and has less depth compared to recordings employing an AB setup.

When the microphones are bidirectional and placed facing ±45° with respect to the sound source, the X-Y-setup is called a Blumlein pair. The sonic image produced by this configuration is considered by many authorities to create a realistic, almost holographic soundstage.

A further refinement of the Blumlein pair was developed by EMI in 1958, who called it Stereosonic. They added a little in-phase crosstalk above 700 Hz to better align the mid and treble phantom sources with the bass ones.^[14]

A-B technique

This technique uses two parallel microphones, typically omnidirectional, some distance apart, capturing time-of-arrival stereo information as well as some level (amplitude) difference information, especially if employed close to the sound source(s). At a distance of about 50 cm (0.5 m) the time delay for a signal reaching first one and then the other microphone from the side is approximately 1.5 ms (1 to 2 ms). If the distance is increased between the microphones it effectively decreases the pickup angle. At 70 cm distance it is about equivalent to the pickup angle of the near-coincident ORTF setup.

M/S technique

Mid/side coincident technique employs a bidirectional microphone (with a figure of 8 polar pattern) facing sideways and a cardioid (generally a variety of cardioid, although Alan Blumlein described the usage of an omnidirectional transducer in his original patent) facing the sound source. The capsules are stacked vertically and brought together as closely as possible, to minimize comb filtering caused by differences in arrival time.

The left and right channels are produced through a simple matrix: Left = Mid + Side, Right = Mid − Side ("minus" means you add the side signal with the polarity reversed). This configuration produces a completely mono-compatible signal and, if the Mid and Side signals are recorded (rather than the matrixed Left and Right), the stereo width (and with that, the perceived distance of the sound source) can be manipulated after the recording has taken place.

Jecklin disk technique

The Jecklin disk technique is similar to A/B recording, with 2 omnidirectional microphones at 36 cm apart from each other. A sound-absorbing Jecklin disk of 35 cm is placed in the middle between the two microphones. The disk makes the apparent separation between the mics much larger than an equivalent A/B recording.

Choosing a technique

If a stereo signal is to be reproduced in mono, out-of-phase parts of the signal will cancel, which may cause the unwanted reduction or loss of some parts of the signal. This can be an important factor in choosing which technique to use.

Since the A-B techniques use phase differences to give the stereo image, they are the least compatible with mono.
Jecklin disk has a relatively small distance between the mics. Frequencies coming in sideways can reach only one microphone and will not interfere. Therefore, Jecklin disk works reasonably well when converted to mono. Jecklin disk also gives phase shifts and amplitude differences matching well with what a real pair of ears would hear at this position and therefore is well suited for headphone playback.
In the X-Y techniques, the microphones would ideally be in exactly the same place, which is not possible – if they are slightly separated left to right, there may be some loss of high frequencies when played back in mono, so they are often separated vertically. This only causes problems with sound from above or below the height of the microphones.
The M/S technique is ideal for mono compatibility, since summing Left+Right just gives the Mid signal back.

The equipment for the techniques also varies from the bulky to the small and convenient. A-B techniques generally use two separate microphone units, often mounted on a bar to define the separation. X-Y microphone capsules can be mounted in one unit, or even on the top of a handheld digital recorder.

M/S arrays can be very compact and fit easily into a standard blimp windscreen, which makes boom-operated stereo recordings possible. They provide a variable soundstage width to match a zoom lens, which can be manipulated in post-production. This makes M/S a very popular stereo technique for film location recording. They are often used in small 'pencil microphones' to mount on video cameras, sometimes even coupled to the zoom.

Related Research Articles

A microphone, colloquially called a mic, or mike, is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public events, motion picture production, live and recorded audio engineering, sound recording, two-way radios, megaphones, and radio and television broadcasting. They are also used in computers and other electronic devices, such as mobile phones, for recording sounds, speech recognition, VoIP, and other purposes, such as ultrasonic sensors or knock sensors.

Binaural recording is a method of recording sound that uses two microphones, arranged with the intent to create a 3D stereo sound sensation for the listener of actually being in the room with the performers or instruments. This effect is often created using a technique known as dummy head recording, wherein a mannequin head is fitted with a microphone in each ear. Binaural recording is intended for replay using headphones and will not translate properly over stereo speakers. This idea of a three-dimensional or "internal" form of sound has also translated into useful advancement of technology in many things such as stethoscopes creating "in-head" acoustics and IMAX movies being able to create a three-dimensional acoustic experience.

Audio feedback is a positive feedback situation that may occur when an acoustic path exists between an audio output and its audio input. In this example, a signal received by the microphone is amplified and passed out of the loudspeaker. The sound from the loudspeaker can then be received by the microphone again, amplified further, and then passed out through the loudspeaker again. The frequency of the resulting howl is determined by resonance frequencies in the microphone, amplifier, and loudspeaker, the acoustics of the room, the directional pick-up and emission patterns of the microphone and loudspeaker, and the distance between them. The principles of audio feedback were first discovered by Danish scientist Søren Absalon Larsen, hence it is also known as the Larsen effect.

<span class="mw-page-title-main">Ambisonics</span> Full-sphere surround sound format

Ambisonics is a full-sphere surround sound format: in addition to the horizontal plane, it covers sound sources above and below the listener.

Surround sound is a technique for enriching the fidelity and depth of sound reproduction by using multiple audio channels from speakers that surround the listener. Its first application was in movie theaters. Prior to surround sound, theater sound systems commonly had three screen channels of sound that played from three loudspeakers located in front of the audience. Surround sound adds one or more channels from loudspeakers to the side or behind the listener that are able to create the sensation of sound coming from any horizontal direction around the listener.

Monaural sound or monophonic sound is sound intended to be heard as if it were emanating from one position. This contrasts with stereophonic sound or stereo, which uses two separate audio channels to reproduce sound from two microphones on the right and left side, which is reproduced with two separate loudspeakers to give a sense of the direction of sound sources. In mono, only one loudspeaker is necessary, but, when played through multiple loudspeakers or headphones, identical audio signals are fed to each speaker, resulting in the perception of one-channel sound "imaging" in one sonic space between the speakers. Monaural recordings, like stereo ones, typically use multiple microphones fed into multiple channels on a recording console, but each channel is "panned" to the center. In the final stage, the various center-panned signal paths are usually mixed down to two identical tracks, which, because they are identical, are perceived upon playback as representing a single unified signal at a single place in the soundstage. In some cases, multitrack sources are mixed to a one-track tape, thus becoming one signal. In the mastering stage, particularly in the days of mono records, the one- or two-track mono master tape was then transferred to a one-track lathe used to produce a master disc intended to be used in the pressing of a monophonic record. Today, however, monaural recordings are usually mastered to be played on stereo and multi-track formats, yet retain their center-panned mono soundstage characteristics.

A DI unit is an electronic device typically used in recording studios and in sound reinforcement systems to connect a high output impedance unbalanced output signal to a low-impedance, microphone level, balanced input, usually via an XLR connector and XLR cable. DIs are frequently used to connect an electric guitar or electric bass to a mixing console's microphone input jack. The DI performs level matching, balancing, and either active buffering or passive impedance matching/impedance bridging. DI units are typically metal boxes with input and output jacks and, for more expensive units, “ground lift” and attenuator switches.

Stereophonic sound, or more commonly stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective. This is usually achieved by using two independent audio channels through a configuration of two loudspeakers in such a way as to create the impression of sound heard from various directions, as in natural hearing.

<span class="mw-page-title-main">ORTF stereo technique</span> Microphone technique used to record stereo sound

The ORTF stereo technique, also known as side-other-side, is a microphone technique used to record stereo sound. It was devised around 1960 at the now-defunct Office de Radiodiffusion Télévision Française (ORTF).

<span class="mw-page-title-main">NOS stereo technique</span> Microphone technique used to record stereo sound

The Nederlandse Omroep Stitchting (NOS) stereo technique is a method of capturing stereo sound.

The Decca Tree is a spaced microphone array most commonly used for orchestral recording. It was originally developed as a type of stereo A–B recording method adding a center fill. The technique was developed in the early 1950s and first commercially used in 1954 by Arthur Haddy, Roy Wallace, and later refined by engineer Kenneth Ernest Wilkinson and his team at Decca Records and its recording studios, to provide a strong stereo image.

Blumlein pair is a stereo recording technique invented by Alan Blumlein for the creation of recordings that, upon replaying through headphones or loudspeakers, recreate the spatial characteristics of the recorded signal.

Gated reverb or gated ambience is an audio processing technique that combines strong reverb and a noise gate that cuts the tail of the reverb. The effect is typically applied to recordings of drums to make the hits sound powerful and "punchy" while keeping the overall mix sound clean and transparent.

Re-amping is a process often used in multitrack recording in which a recorded signal is routed back out of the editing environment and run through external processing using effects units and then into a guitar amplifier and a guitar speaker cabinet or a reverb chamber. Originally, the technique was used mostly for electric guitars: it facilitates a separation of guitar playing from guitar amplifier processing—a previously recorded audio program is played back and re-recorded at a later time for the purpose of adding effects, ambiance such as reverb or echo, and the tone shaping imbued by certain amps and cabinets. The technique has since evolved over the 2000s to include many other applications. Re-amping can also be applied to other instruments and program, such as recorded drums, synthesizers, and virtual instruments.

A Jecklin disk is a sound-absorbing disk placed between two microphones to create an acoustic "shadow" from one microphone to the other. The resulting two signals can produce a pleasing stereo effect on headphones and loudspeakers but are usually not mono-compatible. A matching pair of small-diaphragm omnidirectional microphones is generally used for this technique, although it is possible to use other kinds of microphones resulting in more subtle effects.

In sound recording and reproduction, audio mixing is the process of optimizing and combining multitrack recordings into a final mono, stereo or surround sound product. In the process of combining the separate tracks, their relative levels are adjusted and balanced and various processes such as equalization and compression are commonly applied to individual tracks, groups of tracks, and the overall mix. In stereo and surround sound mixing, the placement of the tracks within the stereo field are adjusted and balanced. Audio mixing techniques and approaches vary widely and have a significant influence on the final product.

Spill is the occurrence in sound recording and live sound mixing whereby sound is picked up by a microphone from a source other than that which is intended. Spill is usually seen as a problem, and various steps are taken to avoid it or reduce it. In some styles of music, such as orchestral music, jazz, and blues, it is more likely to be accepted or even seen as desirable.

In live sound mixing, gain before feedback (GBF) is a practical measure of how much a microphone can be amplified in a sound reinforcement system before causing audio feedback. In audiology, GBF is a measure of hearing aid performance. In both fields the amount of gain is measured in decibels at or just below the point at which the sound from the speaker driver re-enters the microphone and the system begins to ring or feed back. Potential acoustic gain (PAG) is a calculated figure representing gain that a system can support without feeding back.

Apparent source width (ASW) is the audible impression of a spatially extended sound source. This psychoacoustic impression results from the sound radiation characteristics of the source and the properties of the acoustic space into which it is radiating. Wide source widths are desired by listeners of music because these are associated with the sound of acoustic music, opera, classical music, and historically informed performance. Research concerning ASW comes from the field of room acoustics, architectural acoustics and auralization, as well as musical acoustics, psychoacoustics and systematic musicology.

The United Kingdom patent 394325 'Improvements in and relating to Sound-transmission, Sound-recording and Sound-reproducing Systems' is a fundamental work on stereophonic sound, written by Alan Blumlein in 1931 and published in 1933. The work exists only in the form of a patent and two accompanying memos addressed to Isaac Shoenberg. The text is exceptionally long for a patent of the period, having 70 numbered claims. It contains a brief summary of sound localization theory, a roadmap for introduction of surround sound in sound film and recording industry, and a description of Blumlein's inventions related to stereophony, notably the matrix processing of stereo signals, the Blumlein stereo microphone and the 45/45 mechanical recording system.

References

↑ Hodgson, Jay (2010). Understanding Records, p.32. ISBN 978-1-4411-5607-5.
↑ Hodgson (2010), p.34.
↑ Hodgson (2010), p.35-36.
1 2 Hodgson (2010), p.39.
↑ Hodgson (2010), p.40.
↑ Huber, David Miles (2009). Modern Recording Techniques 7th Edition p.141.
↑ Huber, David Miles (2013). Modern Recording Techniques 8th Edition p.141.
↑ "DPA Microphones :: How to: Multimiking a classical orchestra". www.dpamicrophones.com. Retrieved 2015-09-22.
↑ van Eck, Cathy (2017). "Between Air and Electricity. Microphones and Loudspeakers as Musical Instruments", p. 94-98. ISBN 978-1-5013-2760-5
↑ van Eck (2017), p. 110
↑ "Pro Audio Reference". 3-to-1 rule. Retrieved 2024-08-08.
↑ Sams Teach Yourself Digital Video and DVD Authoring, Jeff Sengstack Sams, 2005. Page 88.
↑ Michael Williams. "The Stereophonic Zoom" (PDF). Rycote Microphone Windshields Ltd. Archived from the original (PDF) on 2011-11-28.
↑ Eargle, John (2004). The Microphone Book (2nd ed.). Focal Press. p. 170. ISBN 0-240-51961-2.

External links

Michael Williams, The Stereophonic Zoom
Visualization XY Stereo System - Blumlein Eight/Eight 90° - Intensity Stereophony
Visualization AB Stereo System - Omni/Omni (Spaced) 60 cm - Time-Of-Arrival Stereophony

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[Hodgson-1] Hodgson, Jay (2010). Understanding Records, p.32. ISBN 978-1-4411-5607-5.

[2] Hodgson (2010), p.34.

[3] Hodgson (2010), p.35-36.

[Hodgson39-4] 1 2 Hodgson (2010), p.39.

[5] Hodgson (2010), p.40.

[6] Huber, David Miles (2009). Modern Recording Techniques 7th Edition p.141.

[7] Huber, David Miles (2013). Modern Recording Techniques 8th Edition p.141.

[8] "DPA Microphones :: How to: Multimiking a classical orchestra". www.dpamicrophones.com. Retrieved 2015-09-22.

[9] van Eck, Cathy (2017). "Between Air and Electricity. Microphones and Loudspeakers as Musical Instruments", p. 94-98. ISBN 978-1-5013-2760-5

[10] van Eck (2017), p. 110

[11] "Pro Audio Reference". 3-to-1 rule. Retrieved 2024-08-08.

[12] Sams Teach Yourself Digital Video and DVD Authoring, Jeff Sengstack Sams, 2005. Page 88.

[13] Michael Williams. "The Stereophonic Zoom" (PDF). Rycote Microphone Windshields Ltd. Archived from the original (PDF) on 2011-11-28.

[14] Eargle, John (2004). The Microphone Book (2nd ed.). Focal Press. p. 170. ISBN 0-240-51961-2.

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