Music Production

MICROPHONES

There are a range of different microphone techniques that could be used within a recording session as well as different microphone types and polar patterns. In a recording situation, the microphone choice, setting and placement would be based on the environment you were recording in, the nature of the sound or timbre you were hoping to achieve and the overall depth or clarity of the signal.

Further away from the sound source in a reflective environment (for example) would allow more reflections of the room to be picked up by the microphone and would give a more natural sound, where as close to the sound source will usually deliver a sound with reduced room reflections and a stronger, clearer, more up-front signal. By changing the polar pattern you can control from which direction the microphone will pick up the signal source and/or reflections/room sound.

Microphone Types:

Listed below are the most commonly used types of microphones (Particularly the dynamic and condenser (possibly due to affordability), as well as the featured make and model.

Dynamic (Shure SM58) Condenser (AKG 414B) Ribbon (Nady RSM2) Stereo Condenser (Rode NT4)

When choosing a microphone for a recording task; it is important to chose the right microphone diaphragm size. A large diaphragm microphone will react to the lower frequencies of the hearing spectrum more precisely, whereas a small diaphragm microphone (due to its size) and nature will often deliver a slightly narrower frequency spectrum accenting the clarity of the recording source.

The Difference

Dynamic:

The dynamic microphone is the most robust and durable design of microphone. Its operating principle is based around a light metal coil that vibrates between a magnet when sound is introduced; translating the vibrations of the coil into fluctuations of voltage.

It is not as quick to respond as the condenser of ribbon microphone due to the nature of the mechanism, therefore the transients of a waveform cannot be as accurately represented by the vibrations of the coil and the voltage fluctuations of a dynamic microphone. This means that you will achieve a less-harsh sound in using a dynamic microphone often warmer in overall tone, where as a condenser would deliver a more natural sound with increased fidelity. Background noise or breathing sound for example would be much more easily picked up by the microphone. This also implies that dynamic microphones are better at handling high pressure sound waves such as the inside of a kick drum when beaten.

Condenser:

The Condenser Microphone operating principle is based around a thin polymer membrane mounted on a back-plate; with the freedom to resonate as sound is introduced thus creating fluctuations in voltage (changes in resistance) between the membrane and back-plate resulting in an electrical transduction of the physical vibrations.

They tend to be fragile and simply dropping the microphone can be enough to break it. Over time dust can reduce the sound quality of condenser microphones, therefore it is often good practice to keep them in closed padded flight cases to preserve them.

A Condenser microphone also requires +48V (phantom) power to operate, some have the option of using a battery though it is preferred not to; due to potential hum when in operation.

Ribbon:

The ribbon microphone operates when sound is introduced to a ribbon element. A current is induced at right angles to both the ribbon velocity and magnetic field direction. As the sound wave causes the ribbon to move, the induced current in the ribbon is proportional to the particle velocity in the sound wave.

The ribbon microphone is the most fragile of them all. It can be easily damaged (the ribbon can get stretched) by high pressure sound waves. It is compared to the condenser in terms of the way it can pick up sound and the speed it can react to the transients of waveforms; though it is often praised for its predominance particularly in the high end of the frequency spectrum and its often gritty, rough sound.

Some microphones have been integrated into a moulded human heads with accurately shaped ears. This is in attempts to accurately capture sound as we hear it. This technique has been used to create music referred to as Binaural or binaural beats and is also used heavily for relaxation music such as wind and waves. This technique is good at giving the listener a sound very close to what they would actually hear being in the room at the position of the microphones hearing the sound source as it was played or hearing waves in relaxation music as if your actually sitting by the sea.

It is often a good idea to use microphones with a very good low end frequency response and to ensure the baffle is padded to absorb the high frequencies between the microphones and to create a shadow area such as our head between our ears. It is therefore a level based technique on the low frequencies (high frequency absorption of baffle) and a time based technique on the high frequencies (spacing). The result is a very accurate stereo field; captured in a similar way to how our ears pick up sound.

MICROPHONE PLACEMENT:

Microphones can be placed close, distant, high up, low down, off-axis, inside outside and obviously anywhere/anyway depending on the way you intend to capture the sound source, based on the aspects of it. For example when someone stands in a room whilst somebody beats a kick drum; they would hear all aspects of the drums sound based on the reflective properties of that environment (in various proportions). A microphone on its own does not pick up sound in the same way; due to the fact it’s (usually) a mono signal, it has a different frequency response to our ears and different microphones react at different speeds to the transients of the waveforms (as well as the speed of our ears).

When recording vocals; a certain distance from the microphone (depending on the microphone) should be maintained; to avoid any “proximity effect” issues. This applies particularly when using condenser microphones. It is common place to use a pop filter to avoid any “pop” (pronunciation) issues. This can be avoided further as well as sibilance issues by placing the microphone off-axis to the singer and achieve a less direct signal.

POLAR PATTERNS:

Pictured below are the main polar patterns to which most microphones operate (From Left: Cardioid, Hyper-Cardioid, Bi-Directional/Figure of Eight and Omni-Directional. The majority of microphones are fixed with a specific polar pattern (the most common being Cardioid) though some microphones (such as the AKG 414B) have switchable polar patterns to suit the desired application.

The central point of the horizontal line in the middle of the circle represents where the microphone is situated (facing upwards -plan view).

Therefore if a microphone has a Cardioid polar pattern it will pick up sound mainly form the front (the point at which the signal is strongest; assuming the sound source is central to the microphone), gradually reducing the sound picked up from the sides and only a small amount of sound would be picked up from behind the microphone. If a microphone has an Omni-Directional polar pattern; it will pick up sound equally from all directions.

STEREO MICROPHONE TECHNIQUES:

Although there are a wide range of stereo microphone techniques you can implement in recording sessions; those listed below are the tried and tested techniques, that have been used throughout all kinds of recordings for the last half century.

The various microphone techniques can be used from anything from drum overheads or ambient microphones, to single instruments or even musical ensembles. This is obviously in respect to the sound you hope to achieve based on the characteristics of the microphones as well as the characteristics of the stereo microphone technique itself.

From Left: Coincident Pair, Near Coincident Pair, Spaced Pair

Coincident Pair:

The most clinical microphone that is typically good in MONO and defines an accurate stereo field (in terms of relative position of the sound source in relation to the microphones). The are position at a 90 degree angle to each other, aligned at the tips (diaphragm of the microphones)

This is a level (difference) based technique in terms of the amount of reflections of the room picked up and particularly the position of the sound source in relation to the microphones

Near Coincident Pair:

Again the microphones are positioned at a 90 degree angle to each other, this time aligned at the bottom ends of the microphones rather than the tips. It has a less clinical characteristic than the coincident pair but still sounds good in MONO and again gives an accurate stereo field.

As with the coincident pair it is a level based technique, however due to the slight spacing of the microphones there is an increased time difference between the sound reaching each of the microphones.

Spaced Pair:

The spaced pair is a time based technique due to the spacing of the microphones, this is therefore why phasing becomes a greater issue when using this technique. It is common practice to ensure the microphones are no greater spacing than about 3 - 4' (at equal distance from the sound source) to ensure an accurate stereo field with minimal phase issues.

Baffled Omni:

A more recent stereo recording technique designed to capture sound as accurately as possible to the way which we hear the sound or our ears pick up sound. The polar patterns would be set to omni for this technique and the baffle or divider between the microphones acts as the human head between the ears (microphones).

Some microphones have been integrated into a moulded human heads with accurately shaped ears. This is in attempts to accurately capture sound as we hear it. This technique has been used to create music referred to as Binaural or binaural beats and is also used heavily for relaxation music such as wind and waves. This technique is good at giving the listener a sound very close to what they would actually hear being in the room at the position of the microphones hearing the sound source as it was played or hearing waves in relaxation music as if your actually sitting by the sea.

It is often a good idea to use microphones with a very good low end frequency response and to ensure the baffle is padded to absorb the high frequencies between the microphones and to create a shadow area such as our head between our ears. It is therefore a level based technique on the low frequencies (high frequency absorption of baffle) and a time based technique on the high frequencies (spacing). The result is a very accurate stereo field; captured in a similar way to how our ears pick up sound.

Mid-Side Microphone Technique:

Typically a small diaphragm condenser microphone is pointed at the sounds source at the desired distance and another microphone typically a large diaphragm condenser microphone position at a 90 degree angle. The polar pattern of the large Diaphragm microphone would need to be a bi-directional or figure of eight whereas the small diaphragm microphone would typically be set to Cardioid (though can also be set to Omni or Bi-Directional). The signal from the large diaphragm (Bi-Directional Polar Pattern) microphone would then be split or duplicated in a software DAW and each signal (the original and the duplicate) would be panned left and light. The duplicated signal would then need to have the phase reversed to complete the technique; thus reinforcing the stereo image as seen in the picture below.

Bi-Directional polar pattern on sides would be reinforced by duplicated, phase-reversed signal.

This gives an ultra-wide sound to the signal and good control over the amounts of the Mid Microphone to the side microphone signals. This also sounds good in Mono due to the nature of the balanced signals as well as the positioning of microphones in terms of angle, distance from sound source and polar patterns.