MICROPHONES

In most cases a microphone is the original source of recorded/digital media.

A poor quality microphone and bad recording technique=signal that is noisy, distorted or tonally colored.

A microphone is a transducer- a device that changes one form of energy into another.  A microphone changes sound (changes in air pressure) into an electrical signal (changes in voltage that are analogous to the source).

TYPES

Three types of microphones, depending on mechanism, that create electrical current (fluctuating analogous voltage)- dynamic, ribbon and condenser.

Dynamic- A coil of wire attached to a diaphragm rests in a magnetic field.  When sound vibrates the diaphragm, the coils vibrations in the magnetic field produces an electrical signal that is analogous to the sound waveform.

Ribbon- A thin metal ribbon is suspended in a magnetic field.  Sound vibrates the ribbon in the field, which generates an electrical signal.

Condenser (two types)- A true condenser contains a diaphragm and backplate that are charged from an external voltage and electrets, which are charged from an electret material.  Both can have similar quality, but true condensers are more widely used. A conductive diaphragm and a metal backplate are placed closely together.  They are charged with electricity.  When sound hits and vibrates the diaphragm it varies the spacing between the plates, changing the capacitance*.  This generates a signal analogous to the original sound waves.

*Capacitance is the property of an electrical circuit element that allows it to store a charge in the electrical field between two charged surfaces.

Phantom power- Condensers need an external power source, between 12 to 48 V DC.  Many input devices, such as the Mbox as well as other components like audio mixers, supply phantom power.

Dynamic and Ribbon microphones do not require phantom power, but it could potentially be damaging to them.

General Characteristics of each TYPE (there are always exceptions)

Condensers- Wide, smooth frequency response, detail sound and extended highs, omni has great low-frequency response, Sharp transient attacks, can be small, great general purpose mic.

Dynamic- Not as smooth response, rugged- can take heat, cold and humidity, does not distort at high volume.

Ribbon- Preferred for its warm, smooth tone quality, fragile, good for digital recording.

POLAR PATTERN

This refers to the way the mic responds to signals coming from different angles.  This is similar to the directionality and focus of a video camera.

Omnidirectional- Equal response to sound from all directions.  Good for room tone and acoustics.  Extended low frequency response.  Does not isolate sound.  Not as sensitive to pops (plosives).  No proximity effect.

Bidirectional- Sensitive to sounds from two directions, the front and rear of the mic.  Rejects sounds from sides.

Unidirectional- Most sensitive to sound from one direction (in front) but not as sensitive to sound from sides or rear.  Used to isolate a sound, like a shot-gun microphone on a boom for dialog.  Rejects room acoustics.

Three types of unidirectional microphones-
Cardioid (for heart shape), supercardioid and hypercardiod.  Super and Hypercardioid reject more sound on the sides and are thus more directional, but pick up more sound from the rear.

(See figure 6.5 in handout that plots angle and sensitivity.)

End addressed or Side addressed- how you aim the microphone.

Frequency response- The range of frequencies the microphone will reproduce at an equal level (within a tolerance of say +-3).

Frequency response curve-
Graph of output in dB at various frequencies from about 2-3 feet unless specified.  1kHz is at 0 dB line on graph.

See figure 6.7

Presence peak (microphone is tailored or contoured)- rise in sensitivity around 5-10kHz.  Sounds crisp/sharp and adds punch, because it empahsizes higher harmonics (frequencies).

Proximity effect- Unidirectional and Bidirectional microphones boost bass when used a few inches from source.   Ex. Voice sounds bassy or boomy.  Plotted on freq.-response graph.  Can be good for drums though.  Some mics have bass roll-off.

Example

Mic Accessories-

Pop filters- Filter out unwanted sound from plosives, “p”, “t,” or “b,” the turbulent puffs of air, called pops, from a singer or narrator.  Best is nylon screen (or foam sock) over a hoop placed a few inches from the mic.

Windscreen- Foam or furry “sock.”

Stands and booms

Shock mounts- Holds mic in a suspension to isolate it from vibrations etc.

Cables and connectors- Best balanced cables, remove interference.  Ex. XLR and 1/4 inch balanced.

RECORDING THE VOICE

Concerns in recording the voice are proximity effect, breath pops, wide dynamic range, sibilance and sound reflections from music stand.

Miking Distance-

To prevent proximity effect mic at distance of 8 inches.  A flat response condenser with a large diaphragm is a good choice.

Vocalist should maintain distance to mic.

Pops- Use pop filter, and microphone placement.

Wide dynamic range- Singers have a wide dynamic vocal range (soft or loud).  Proper microphone technique- back away on louder sections, move in close on softer ones.  (Studios use compressors, which is an electronic device that acts like an automatic volume control.)

Sibilance- This is the emphasis of the “s” or “sh” sounds (around 5-10 kHz.)  Can be obnoxious.  Use a mic with flat response (without presence peak).  Or use a de-esser signal processor, which cuts the highs only on sibilance.

Vocal effects- Stereo reverb, echo, doubling, best to add effects later in mix.

MICROPHONE PLACEMENT

The best thing to do is to listen with good headphones.

Listen for good signal to noise ratio.

Microphones place close sound close and tight, mics placed farther sound distance, have more room sound and pick up sound from other elements.

Microphones placed more than 10 feet away are called ambience mics- they pickup mostly room echoes and reverberations.