Glossary

Absorption coefficient - the amount of acoustic energy a material absorbs in relation to what it reflects 



Acoustic Isolation -  the prevention of external noises from
transmitting into the studio environment through the air, ground or
building structure. It can also prevent excessive volume levels
from leaking into the surrounding neighborhood.



Acoustic separation - the separation of rooms so that 
music doesn't bleed into other rooms during the recording process.
Also needed to keep environmental noises like heat vents or refrigerator hum
from interfering with intelligibility of the recording. Often a requirement for
ensuring that sounds from one instrument aren't unduly picked up by
another instruments microphone.



Bars Bars are a measurement term for air pressure.



Compression - compression is a period of high pressure.



Diffuser   - a Diffuser is a device used in studios to reduce standing waves



Dynamic Range Dynamic Range includes the amplitude of the waveform itself and the amplitude.  
All real world non-textbook wavefroms contain random variations. and so on.


Floating floor is a floor that is isolated from the mechanical vibrations of the structure around it.



Fourier Theorum The Fourier Theorum states that all waveforms can 
be represented as the sum of various sinewaves. 
(See: Inverse Fourier Transform)
 


Frequency Balance - The frequency components of a room shouldn't
adversely affect the acoustic balance of instruments and/or
speakers. Simply stated, the acoustic environment shouldn't alter
the sound quality of the original or recorded performance.



Fundamaental The Fundamental is the lowest frequency a device produces.



Inverse Fourier Transform - The Inverse Fourier Transform is the mathematical 
tool for recreating a waveform, Starting with its Fourier Transform. 
This relationship takes into account both the amplitude versus frequency 
and the phase versus frequency analysis 
to recreate the original waveform. 
Even where amplitude analysis, it is their phase analysis that separates them.



Microphone - A microphone is a device that converts acoustic energy into corresponding electrical voltages that can be amplified and recorded. In audio production, three transducer types are used, Dynamic mics, condensor mics and ribbon mics.
Dynamic Mics - A dynamic Mic operates by using electromagnetic induction to generate an output signal. The theory of electromagnetic induction states that, when ever an electrically conductive metal cuts across the flux lines of a magnetic field, a current of a specific magnitude and direction will be generated within that metal. Dynamic mic designs generally consist of a stiff Mylar diaphragm of roughly 0.35 mil thickness. Attached to the dipragm is a finely wrapped core of wire(called a voice coil) that's precisely suspended within a high level magnetic field. Whenever an acoustic pressure wave hits the diapragm's face, the attached voice coil is displaced in proportion to the amplitude and frequency of the wave, causing the coil to cut across the lines of magnetic flux that's supplied by a permanent magnet. In doing so, an analogous electrical signal (of a specific magnitude and direction) is induced into the coil and across the output leads.  
Ribbon Mics - 
Condenser Mics - Condensor Mics operate on an electrostatic principle. The capsule  of a basic condenser mic consists of two very thin plates-one movable diaphragm and one fixed backplate. These two plates form a capacitor (or condensor as it's still called in the UK and in many parts of the world). A capacitor is an electrical device capable of storing an electrical charge. The amount of charge that a capacitor can store is determined by its capacitance value and the voltage that is applied to it.according to the formula:
                                                      Q=CV
Where Q is the charge in Colombs), C is the capacitance (in farads), and V is the voltage measured in volts.
The capacitance of a capsule is determined by the composition and surface area of these plates (which are fixed in value), the dielectric or substance between these plates (which is air and is also fixed) and the distance between the plates (which proportionately varies with sound pressure). From this it's fairly easy to see that plates of a condenser mic capsule form a sound-pressure-sensitive capacitor.    
	Commonly, the plates of a condenser capsule are connected to opposite sides of a stable DC power supply, which provides a polarizing voltage to charge the capacitor. Electrons are drawn from the plate connected to the positive side of the power supply and are forced through a high-value resistor onto the negatively charged plate. Once powered, the capsule charges to a state whereby the charge (thedifferen ce between the number of electrons on the positive and negative plates) is equal to the capsule capacitance times the polarizing voltage. Once this equilibrium is quickly reached, no further appreciable current flows through the resistor. It's at this point that the device can start acting like a microphone. Once a sound-pressure wave falls upon the diaphragm, its capacitance changes. When the distance between theplates decreases, the capacitance will increase; conversely, when the distance increases the capacitance will decrease. According to    
(Source: Huber, David Miles. Runstein, Robert E. Modern Recording Techniques. Sixth Edition. 116-117)
   


Nodes Nodes are when waves cancel each other out.



Phase - Phase is used to refer to when a waved cycle starts in time. 
Always a comparative relationship. It is measured in degress. 
The cycle starts at zero, reaches compression at 90 degrees, 
crosses over the zero point at 180 degrees, comes to rarefaction at 270 degrees
and completes its cycle at 360 degrees.
 


Rarefaction - Rarefaction is a period of low pressure.



Relative Phase  - Relative Phase is the difference in time between two waves.
It is always a comparative relationship.

Resonance - the sympathetic or induced vibration of a system (a solid, air space or a membrane) in response to vibrations 



Reverberation - The control of sonic reflections within a space is
an important factor for maximizing the intelligibility of music and
speech. No matter how short the early reflections and reverb times
are , they will add an important psycho-acoustic sense of space in
the sense that they can give our brain subconscious cues as to a
rooms size, number of reflective boundaries, distance between the
source and listener.


Sound Sound is changes in air pressure that can be sensed by the ear.
Air pressure changes must change from one state to another and then back again.
 


Standing waves, also known as room modes, occur when sound is
reflected off of parallel surfaces and travels back upon its own
path, thereby causing phase differences to interfere with a rooms
amplitude response. Room modes are expressed as integer multiples
of the length, width and depth of the room and indicate which
multiple is being referred to for a particular reflection.

Standing Waves - sound waves that reflect off of parallel surfaces and travel back on their own path.

Walking around a room with moderate to severe mode problems 
produces the sensation of increasing or deceasing volume levels at
various frequencies throughout the room. These perceived volume
changes are due to amplitude (phase) cancellations and
reinforcements of the combined reflective waveforms at the
listener's position. The distance between parallel surfaces and the
signals wavelength determines the nodal points that can potentially
cause sharp peaks or dips at various points in the response curve
(up to or beyond nineteen dB) at the affected fundamental frequency
(or frequencies) and upper harmonic intervals.



Transmission loss refers to the reduction of a sound signal (in dB)
as it passes through an acoustic barrier.
TL = 14.5 log M + 23 
TL is in Decibels

M is the surface densities or combined surface densities of a
barrier in pounds per square foot (lb/ft\uc0\u178 )
Because transmission loss is frequency dependent, the following
equation can be used to calculate transmission loss at various
frequencies with some degree of accuracy:

TL = 14.5 log Mf - 16
Where f is the frequency in hertz

Heavier acoustic barriers will will yield a higher transmission
loss. For a given acoustic barrier, transmission losses will
increase as the frequency rises.

Transmission loss - Reduction in the SPL of a signal as it passes through a medium



Waveform
A wave forms Cycle goes from its resting point, to compression 
to rarefaction and then back to its staring point. 




Cost Factors - Not the least of all design and construction factors
is cost. Multimillion-dollar  facilities often employ studio
designers and construction teams to create a plush decor that has
been acoustically equipped to fit to fit the needs of both their
owners and their clients. Owners of project studios and budget
minded production facilities, however, can also take advantage of
the same acoustic principles and construction techniques and apply
them in cost effective ways.  


, or on two sides of the mic, but not all the way around.

Cardioid �?ECardoid Mics pick up sounds on a heart shaped pattern.
Some Cardoid mics pick up more sound in their weaker direction that
others, but are stronger on one side for sure.

2. Describe the proximity effect.
The Proximity Effect is a low frequency phenomenon that occurs in
most directional mics. Whenever a mic is brought one foot of a
sound source there is an increase in bass response. It
proportionately increases as distance decreases. To compensate for
this effect low frequency roll off filters are built into many
mics. An external equalizer can also be used to bring bass response
to a flat natural balance. This effect is more common with
directional than omnidirectional mics.

3.) What determines a Mic⤁s Transient Response?

A Transient Response is the measure of how quickly a mic's
diaphragm will react when it is hit by an acoustic wavefront. This
figure varies widely among microphones and is a major
reason for the difference in sound quality among the three pickup
types. For example, the diaphragm of a dynamic mic can be quite
large (up to 2 1/2  inches). With the additional weight of the coil
of wire and its core, this combination can be a very large mass
when compared to the sound wave that drives it. Because of this, a
dynamic mic can be very slow in reacting to a waveform-often giving
it a rugged, gutsy, and less accurate sound.

By comparison the diaphragm of a ribbon microphone is much lighter,
so its diaphragm can react more quickly to a sound wave form,
resulting in a clearer sound. The condenser pickup
has an extremely light diaphragm, which varies in diameter from 2
1/2 inches to less than 1/4 inches and has a thickness of about
0.0015 inch. This means that the diaphragm offers very little
mechanical resistance  to sound pressure waves, allowing it to
accurately track
the wave over the entire frequency range.


Greg Spence Wolf   Music tech 220 Section 3   11/30/05

Distant Miking
With distant miking one or microphones are positioned at a distance
of three feet or more from the intended signal source. This
technique can pick up a large portion of a musical instrument or
ensemble. Thereby preserving the overall tonal balance of that
source. Often a natural tone balance can be achieved by placing the
mic at a distance that's roughly equal to the size of the
instrument or the sound source.
It allows the rooms acoustic environment to be picked up and
Naturally mixed in with the direct sound signal.
Distant miking is often used to record large instrument ensembles
like symphony orchestras or choral ensembles. In this application
the pick up will rely on the acoustic environment to help achieve a
natural ambient sound. 
The mic is placed at a distance so as to strike an overall balance
between the ensembles direct sound and the room's acoustics. This
balance is determined by a number of factors including the size of
the sound source, its overall volume level, and mic distance and
placement, as well as the reverberant characteristics of the room.


Distant miking techniques tend to add a live open feeling to a
recorded sound. This technique could prove to be a disadvantage if
the acoustics of the room you are recording in aren't very good.
(Huber and Runstein137-138)

Close Miking
 Close miking techniques refers to when the mic is placed between
one inch and three feet from the sound source, this technique
generally yields two results:
-It creates a tight, present sound quality.
It effectively excludes the acoustic environment.
Because sound diminishes with the square of its distance from the
sound source, a sound that originates three inches from the pickup
will be much higher in level then one that originates 6 feet from
the mic. Therefore whenever close miking is used, only the desired
on-axis sound will be recorded-while extraneous distant sounds won't
be picked up. Whenever an instrument's mic also picks up the sound
of a nearby instrument, a condition known as leakage occurs. This
can cause phase cancellation and make the mix-down process more
difficult.
To avoid leakage, any or all of the following methods can be used.
-Place the mics closer to their respective instruments
-Place an acoustic barrier between the two instruments
-Use directional mics.
-Spread the instruments further apart.
-Use the 3:1 distance rule.
 --Which states "In order to reduce leakage and maintain phase
integrity, for every unit of distance between a mic and its source,
nearby mics should be separated by at least three times that
distance. 
Close miking can also lead to the mics picking up only the timbre
of one part of the instrument, and not the whole instruments sound
qualities.

X/Y Miking patterns
X/Y stereo miking is an intensity-dependent system that uses only
the cue of amplitude to discriminate direction. With the X/Y
coincident-pair technique, two directional microphones of the same
type, manufacture and model are placed with their grills as close
together as possible without touching and facing at angles to each
other - generally between 90 and 135 degrees. The midpoint between
the two mics is pointed at the source, and the mic outputs are
equally panned left and right. Even thought the two mics are placed
together, the stereo imaging is excellent - often better than that
of a spaced pair. In addition, due to their close proximity, no
appreciable phase problems arise. Most commonly, X/Y pickups use
mics that have a cardioid polar pattern.
  
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http://harada-sound.com/sound/handbook/defa-d.html

Attenuate / Attenuator / Attenuator Pad - In electronics, to "attenuate" is to decrease the level of a signal. An "attenuator" is a device, usually a passive network, that accomplishes this task with negligible distortion, although in some cases attenuation is unintentional, such as the signal drop caused by using a long length of wire for transmission. In sound, attenuators are usually used to lower the level of an audio signal in a system to prevent overload and distortion. The network of resistors, inductors, and capacitors is also referred to as a "pad," or "attenuator pad." There are two basic types of pads, which differ in their network topology: L-pads and T-pads. A true L-pad network includes two variable potentiometers that are ganged together, which provides a constant input or output impedance regardless of attenuation. A volume control is a common example. While an L-pad network has two "legs" in its network, a T-pad network has three.Some microphones have a built in attenuator pad on the output stage of the microphone, reducing the output level by 10 or 20 dB, to prevent overloading the input stage of a mic preamplifier. Most mixing desks, too, have some sort of attenuator pad switch, reducing the level to the input stage of the channel by 15 or 20 dB.

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What is a pad? Is it the same as an attenuator?

A description of the technology and function of the pad (attenuator) as found in mixing consoles.
 

What is a pad? Is it the same as an attenuator?

The mic preamp (preamplifer) is where the input signal is conditioned so that it is suitable for further processing in the console.

In some mixing consoles and mic preamps, the lowest gain setting is insufficiently low to cope with very high output levels from the microphone.

In this case there will probably be a 'pad' switch. A pad is an attenuator - it makes the signal smaller.

Usually, the pad reduces the signal level by 20�dB.

In a well-designed console, the pad should be positioned before the active circuit components. This means that, when active, the pad cuts down the signal level before it has the chance to cause any distortion.

Another reason to use the pad is if it is found that the fader on that channel is inconveniently low. When the fader is low down, it is difficult to adjust accurately.

So if you need to have precise control over a signal that is only required at a low level in the mix, it is handy to use the pad to allow the fader to be placed higher up in its range.


http://www.record-producer.com/learn.cfm?a=162&c=post

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High and Low Cut filters

As their name implies, the Low Cut and High Cut filters eliminate frequencies at the extremes. The Low Cut filter, for example, eliminates low frequencies, while leaving high frequencies mostly unchanged. This is extremely useful for eliminating rumbling sounds from a track. It can also be used as a more noticeable effect, such as thinning out a lead instrument so it cuts through a mix better.

The High Cut filter, though it's typically less used than the Low Cut filter, can be used for reducing high frequency noise, such as is found on bass and kick drum tracks. It can also be used to soften a harsh-sounding track such as an overly distorted guitar track.

High Cut and Low Cut filters offer only one control: frequency. This is the "knee" point past which most sounds are eliminated. For example, a Low Cut filter with the frequency set to 200 Hz will eliminate most sounds below 200 Hz and leave sounds above 200 Hz more or less untouched. Similarly, a High Cut filter with the same frequency setting will reduce most sounds above 200 Hz and keep most sounds below 200 Hz.
http://www.xowave.com/doc/tutorials/eq/
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Microphone Technology 101�Basic Terminology and Techniques for Stage and Studio
By George Petersen
May 18, 2004 12:00 PM
BASIC TERMINOLOGY AND TECHNIQUES FOR STAGE AND STUDIO
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Microphones are a key factor in achieving high quality recordings and sound reproduction. Having access to top-notch equipment helps, but more importantly, some knowledge about mic basics and a few simple tips and tricks can make a substantial difference on your next project.

There are two common categories of mics used in professional audio. Dynamic types operate when sound waves strike a diaphragm attached to a coil of wire. When the coil moves within the magnetic structure of the microphone, this creates an output voltage. The process is exactly the reverse of the way a speaker operates. One variation of the dynamic approach is the ribbon mic, which uses a thin ribbon of metal that is placed between the poles of a magnet. Note that most ribbon mics are bidirectional, meaning they pick sounds equally well from either side of the mic.

Condenser mics use an electrically-charged, metallized diaphragm, placed very close to a conductive back plate and separated by a thin air layer. Sound waves striking the diaphragm cause a very small voltage change, which is increased by a tiny amplifier circuit within the mic body. As power is required by both the mic capsule and the amplifier, condenser mics must have a power source, which can be a battery inside the mic body or "phantom" power coming from either the mixing console or an external power supply.

Dynamic mics tend to be extremely rugged, making them especially well-suited for sound reinforcement applications. However, the extremely thin, low-mass diaphragms used in condenser mics provide improved high-frequency response, with better reproduction of fast transient signals. Therefore, condenser mics are usually the best choice for instruments such as piano, cymbals, and stringed instruments.

With many instruments, two mics arranged as a stereo pair offer optimal reproduction. One popular arrangement is the "X-Y" configuration, where the capsules of two mics are spaced a few centimeters apart, with the left mic pointed to the right and vice-versa. Another stereo technique uses a "spaced pair", with the two mics placed parallel to each other and at least 50cm apart. The X-Y method offers a stereo image that retains consistent level when the recording is played in mono. The spaced pair technique provides a more dramatic stereo effect, but extreme left and right sounds may be emphasized more than sounds coming from the center. Both of these stereo techniques are frequently used on stage and in the studio, particularly for piano, orchestra, and above drum sets, large percussion setups, vocal choirs and horn or string ensembles.

Acoustic guitars can be miked in a number of ways, and condenser mics are best in this application. While a stereo X-Y pair works well, some unconventional methods can offer good results. A miniaturecondenser lavalier microphone can be taped or clipped inside the guitar and mixed with a second mic placed outside the guitar, pointing toward the soundhole. In a quiet studio, mics can be placed one or two meters away, offering a full, mellow sound. If more string or pick noise is desired, the mics can be placed closer.

Electric guitar speakers usually require no more than placing a single dynamic mic pointed toward the cabinet. However, the sound of a speaker varies widely when the mic is placed in different locations on the speaker. Moving the mic even a few centimeters can make a major difference, so it pays to experiment to find the "right" sound.

Generally, electric bass is not miked, but is usually connected to a direct box. Sometimes, this direct sound can be combined with a mic placed in front of the bass amp. In this case, the direct signal must be delayed�usually 1-5 milliseconds�to align the phase (timing) of the two signals.

As with electric bass, synths and electronic keyboards are usually connected to direct boxes or routed from the submixer in the keyboardist's rack. One exception is the Leslie speaker connected to a Hammond organ. Since the Leslie speaker consists of a bass speaker with an rotating horn above, one upper and one lower mic are required. The output of these can be mixed to provide a variety of effects, ranging from subtle to dramatic, especially when the upper rotor is miked in stereo, using two mics!

Acoustic grand piano can be a difficult instrument to reproduce, where the microphone method depends largely on the other instruments in the room. When recording solo piano, a stereo pair of mics is often placed at a distance, to capture the room ambience. Unfortunately, this approach doesn't work well on stage with a rock and roll band�here, close-miking is required. Depending on the piano, two condenser mics in a variation of either spaced pair or X-Y generally work well, with the lid raised open and the mic capsules placed 10-20cm above the strings. A brighter sound results when the mics are placed close to the strings. If sound leakage from other instruments is a problem, then the lid can be (carefully) lowered, or a heavy blanket can be placed over the piano top.

Most horn and reed instruments have a slightly harsh character and sound better through ribbon or large-diaphragm dynamic or condenser mics, especially at close distances. However, small diaphragm condenser mics offer a little high frequency "edge" that can help solo instruments stand out. Several companies�such as AKG, Audix and Shure�manufacture miniature condenser mics with clamps for mounting on saxophone or trumpet bells, and these are ideally suited for wireless mic applications.

Drum and percussion miking presents a major challenge to any sound engineer. These are extremely loud instruments that cover an exceedingly wide frequency range, no to mention the fact that placing mics within a maze of drum stands can be a difficult task, indeed. Another problem is placing mics out of range of flailing sticks! As mentioned earlier, an overhead stereo pair can be used to pick up cymbals or to cover a large percussion setup. Condenser mics are the best choice here, since they are placed out of harm's way and offer excellent high-frequency response.

Dynamic mics are most often used for snares, tom-toms, conga, timbales, bongos and other drums�one secret to getting a good sound here is to make sure that the mics are placed above the drum and pointed downwards. When the microphone is placed parallel (or at a slight angle) to the drum, then most of the sound energy strikes the side of the mic, resulting in a thin, weak sound. If you do not have enough mics (or console inputs) for each individual drum, then a single mic can be placed between two adjacent drums.

Getting a solid bass drum sound can be tricky. Removing the front head of the drum and placing a blanket or pillow against the beater head may be the first step. Whatever you do, keep your condenser and ribbon mics away from the bass drum, whose sound output can permanently deform a delicate diaphragm! A large-diaphragm dynamic mic offers the right combination of low-frequency response and the ability to reproduce high sound pressure levels to do the job. A little EQ also helps�a boost at 1.5kHz adds more attack, while a cut at 400-600Hz can reduce excessive boominess for a tighter sound.

Years ago, I became hooked on using electronic kick drum to trigger samples on rock, pop and R&B dates�even when I was recording an otherwise all-acoustic kit. This approach offer many advantages: As the kick is silent in the studio, sympathetic snare buzz is greatly reduced, and the overall signal in the overheads is cleaner, with less kick bleeding into the other mics. Also, with no bleed from the original kick, the kick patttern can be changed or altered later if necessary�a highly desirable option. On any session (sampled or otherwise), the goal of recording kick is to get a solid, consistent sound�and here the sampled kick adds�rather than detracts�from the drumkit sound.

Whether onstage or in the studio, getting a great sound requires good equipment and the application of fundamental techniques. Remember that there is no single correct method that works in all cases, and sometimes a bit of experimenting with angles and microphone placement really pays off. Be creative!

Note: This article first appeared in the Spanish language edition of Mix magazine and has been translated to English from the original.

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