Transcript
Computer Skills Sound Production AA604
sound Air is a mass of densely packed molecules of various gases. The air at sea level is under pressure due to the kilometers of air pushing down from above. Sound travels through the air, the speed of sound is relative to how closely the air molecules are packed. Therefore the speed of sound is relative to the prevailing air pressure The air around us is like jelly if one part of it moves the other parts react, it “wobbles”. This sea of “jelly” also has properties like a rubber band, if you stretch it and let go it snaps back. The stretching and wobbling is what we hear with or ears and our brains decipher as sound. If the air is stretched we call it rarefaction or low pressure. If the air is squashed we call it compression or high pressure. The high and low pressure can be plotted onto a graph and displayed over time this is known as a waveform. The changing of the high to low when measured over time is known as the frequency. Frequency is expressed in a linear scale known as Hertz or Hz. Hz is a calibration that means times per second Human hearing starts at about 20Hz and goes up to about 20,000 Hz or 20KHz (kilohertz)
sound production equipment An electrical current moving through a wire will create a magnetic field around it. Like wise when as wire is surrounded by a magnetic field an electrical current will eventuate, this is known as induction.
the dynamic microphone Inside dynamic microphone is a thin membrane or as it is known a diaphragm. The diaphragm responds to the movement in the air caused by rarefaction and compression. Attached to the back of the diaphragm is a “coil” of wire. This coil of wire moves when the diaphragm moves, there for the coil moves in relation to the frequency of the air movement/sound. The coil surrounds a magnet fixed in place in relation to the moving coil. The magnet subsequently produces a tiny electrical current. This induced current then changes its frequency in analog to
the dynamic microphone cont. the changing air pressure as the coil moves back and forward within the magnetic field. The frequency of fluctuations in the coil’s induced voltage can be recorded as an electronic signal and played back as a sound through a speaker (a speaker works in reversal to a dynamic microphone) The Dynamic Microphone is sturdy and well suited for use in video work, it does not require an external power supply. It is not however sensitive to high frequency, for acquisition of high frequency audio a condenser microphone should be considered.
the condenser microphone The condenser microphone like the dynamic microphone also produces a changing voltage that is analogue to the changing air pressure, however the signal is derived in a very different way. As the dynamic microphone works with induction the condenser microphone works with capacitance. When two conductors (materials that easily carry an electric charge) charged in opposition to each other, that is one has a positive charge and the other is charge negative, then a “potential difference’ exists between them. Potential difference simply explained is the build up of electrons on one of the conductors to the point before they jump the gap to the opposite conductor. Much the same as a cloud builds up potential difference prier to a lightning strike. This potential difference is known as “capacitance”. If one of the conductors is a microphone diaphragm that moves in unison with the changing air pressure and the other conductor is in a fixed position relative to the diaphragm at rest, then as the diaphragm moves the capacitance between the two conductors changes. It is the change in capacitance that creates the audio signal in a condenser microphone. Since the condenser microphone diaphragm dose not carry a coil it moves more freely then that of a dynamic microphone, consequently it is has increased sensitivity and can attain much higher frequencies in comparison. Because it is so sensitive the condenser microphone is prone to overloading, that is oscillating beyond its specified frequency range due to a high volume air pressure wave, thus causing distortion. A condenser microphone requires an external power source to charge its conductors, usually in the form of an onboard battery, however it can also be powered via the cable that connects it to the recording devise or mixer. This “unseen” type of power is known as Phantom Power.
the condenser microphone cont. Most good condenser microphones have an in-built signal amplifier consequently an audio signal from a condenser microphone has a greater amplitude then that of a dynamic microphone. The signal voltage that comes from a microphone is known as “mic” level as opposed to the higher voltage signal that comes from an amplifier or other electronic equipment such as a VCR or audio mixer. This higher signal is known as “line “ level. Most audio inputs and outputs or clearly marked. Some sound devices (almost all professional video cameras) have only one connection that is switchable from line to mic and vice versa. (You can tell if the switch on a switchable sound device is set at the wrong level by listening to the output on an audio monitor, if the level is high the monitor will distort if the level is to low the monitor will playback faint sound.
microphone response patterns omni-directional An omni-directional response pattern means that a microphone will pick up sound equally from all directions. Although “Omni’s” as they are known, tend to pick up less handling “noise” the 360° response pattern limits there use to recording ambient sound, this makes them perfect for recording speakers at a table conference table. Lapel microphones mostly have an omni-directional response pattern.
Cardioid Cardioid microphones have a greatest response from directly in front of the diaphragm. They pick up little from the sides and almost nothing from the back. Cardioid microphones have a response pattern that resembles a heart shape hence the name “cardi” from cardiac. Cardioid microphones are ideal from recording a speaker in noisy environments as they exclude sound from behind the microphone.
bi-directional Bi-directional microphones have a figure 8 response pattern. Bi-directional microphones are less common in video production however they are useful when recording an interview between two people by avoiding the problem of having to move the microphone from one person to another.
hemispherical Hemispherical microphones have a dome shape response pattern they work with assistance from the area they are placed upon. Usually placed on a hard surface the hemispherical microphone tends to rely on the reflective properties of that surface for the quality of the sound that it responds to.
microphone types shotgun Shotgun microphones are the best all round microphones for use in video and film location applications. The shotgun microphone has a highly directional Cardioid response pattern that is produced by placing the microphone “capsule” at the end of a long thin tube. A series of slits along the tube creates a cancellation effect to sound coming from the side of the microphone. The distinctive design of the microphone is long and narrow much like the shape of a shotgun hence the name.
CARDIOID SHOTGUN POWER MICROPHONE
pzm The PZM or pressure zone microphone is a cheap, very effective way of recording ambient or atmos audio. When the PZM is mounted on a table, wall or floor, all sound from that surface is reflected into a small microphone at the centre of a hemispherical response pattern. The PZM is useful in round table discussions however it is very sensitive and will easily pick up the sound of rustling paper and other sound that is close to the reflection surface.
sound is vibrations in air pitch is the speed of the sound or air pressure vibration, fast vibration is treble, and slow vibration is bass waves are ripples of sound. Sound travels in waves that are measured in frequency e.g. waves per second waves per second are called hertz - Hz 100 Hz = bass 15,000 Hz = treble amplitude is the height of a wave, the greater the amplitude the louder the volume Big vibration = Big amplitude = Big volume Small vibration = Small amplitude = Small volume decibels is the measurement for volume dB If hearing starts at 0dB Speaking 60dB Lawn mower 100dB Jack hammer 110dB Rock band 115dB Ears hurt 110 - 120dB Jet take off 140dB* the proximity effect The closer you get to the microphone the more volume and base response is reproduced it is harder for the microphone to handle sound up very close. echo is caused by sound bouncing of “live” walls cycle is one complete rise and full of a wave wave length is the length of a wave peak to peak or trough to trough high frequency is lots of cycles per second
Frequency Range
Hz 16 & 32 32 & 64 64 & 128 128 & 256 256 & 512 512 & 1,024 1,024 & 2,048 2048 & 4,096 4,096 & 8,192 8,192 & 16,384
}
Octave
}
first second third forth fifth sixth seventh eighth ninth tenth
doubles
Range of hearing
• Harmonics, other frequencies in the same sound with a different octave. e.g. all A notes have the same primary frequency, some have secondary and tertiary vibrations or frequencies (harmonics) All sound includes Attack time, Sustain time and decay time S o u n d
P r e s s u r e
Peck Sustain sound level Decreasing sound level
Attack
Sustain
Decay
TIME
balanced & unbalanced audio In the production of audio the most common type of cable used is Balanced audio cable. Balanced cable is used to redirect the interference from stray electromagnetic field. Induction is used in the case of a dynamic microphone to produce an audio signal however Induction can also be a source of interference to a signal. If an audio cable is placed near an electromagnetic field such as a standard 240volt power lead, the induction produced by the power cable can interfere with the audio signal in the audio cable. A balanced audio cable has an outer shield of woven wire. This shield acts a “drain”. When a balanced audio cable passes
balanced & unbalanced audio cont. through an electromagnetic field the outer shield collects the stray induction and prevents it from interfering with the audio signal. An unbalanced cable has no such shield and is only useful over very short distances were there is no chance of interference. Balanced Cable/connector 3 pin XLR * Pin 1 - Shield or earth * Pin 2 - Live or hot * Pin 3 - Return or cold
Inner live & return wires pins 2 + 3 Outer shield pin 1
The shielding in balanced cable reduces the Amount of interference from electrical fields and radio. The two inner cables carry the circuit the outer shield protects against interference. Unbalanced Cable/connector 1 inner wire 1 outer shield Unbalanced cables are subject to interference. The inner cable and outer shield carry the circuit.
Inner wire Outer shield
phantom power Dynamic microphones use sound energy to create voltage. Some condenser microphones have a static charge on the pick up others use a battery to produce a charge. Phantom Power symbolized by 48V, uses power supplied through the cable from the device to which it is connected, provided that that device is phantom power compatible.
audio meters VU METERS 7 VU = Volume Units 10 VU meters measure average levels 20 0dB is a good signal however if the signal is peaking it is better to record a weaker signal than have one which distorts. If the signal is to weak then more back ground Noise will be relevant when the signal is boosted (there is a lower signal to noise ratio).
PPM PPM = Peak Program Meter PPMs proved a peak level indication and hold that level for about a second a good signal should peak around 0dB.
5
3
0
+3
Glossary of Audio Terms absorption coefficient: A measurement of the ability of a given material to absorb and/or transfer sound. Measured in sabines (after Dr. Wallace Sabine who created the system). acoustics: The study of sound. Also, the property of an enclosed environment, and how that environment affects the transmission of sound within it. ADR: Automatic dialogue replacement, otherwise known as "looping". The process of replacing "live" dialogue with studio-recorded (and therefore clean) dialogue. Used predominantly in the film industry. ambience: The acoustic "signature" of a specific environment (usually, but not always an interior environment), it is made up of the characteristic sound reflections within that environment. amplifier: In common usage, a device used to boost a signal’s strength so that it may drive a loudspeaker. More technically, this term relates to a family of devices, which may or may not affect a signal’s gain. A "distribution amplifier", for instance, will take a single signal input and duplicate it into several identical out puts. A "head amplifier" is used to get mic level inputs up to line level. A "summing amplifier" is used within a mixing console to add the out puts of any number of faders into a single output, its impedance being such that the signal from any one fader cannot return back up another fader’s channel. In short, then, an amplifier is a circuit or portion of a circuit that prepares the signal for the next part of its journey, without altering its characteristics. amplitude: The extreme range (height and/or depth) of a signal wave form. Measured from the average (or mean) to the extreme, amplitude corresponds to the level (loudness) of a sound. analog: A method of sound reproduction utilizing an electrical signal that fluctuates in frequency and amplitude in direct proportion to the sound wave it is replicating. anechoic chamber: A room in which the walls offer essentially 1000 /n absorption, therefore simulating free-field conditions A room without echoes antinodes: The high SPL point of a standing wave, corresponding to the peak of the related wave form, articulation: In speech, the way in which words are joined; the connections (and disconnection) between words. Clear articulation is important for the intelligibility of spoken words.
attenuation: The term given to the process of reducing a signal’s gain. auditory canal: Also known as the ear canal, it begins just inside the ear (at the edge of the pinna) and extends to the eardrum. axis: The line through the centre of, and at right angles to, the plane of a microphone’s diaphragm, or speaker cone. If you are pointing a microphone directly at a sound source, you are said to be "on axis". Like-wise, if you are having trouble hearing a PA because you are sitting behind the stack of speakers, you are definitely "off axis". Since high frequencies are easier to focus into a beam of sound (for instance, ultrasound devices as used in medical procedures), "on axis" leads to the maximum high frequency response. azimuth: The angle that the head gap on a tape recorder makes in relation to the travel of the tape. For a standard audio tape recorder, this angle must be 90 degrees. backing: The base material on which the coating of magnetic medium is supported in tape systems. It needs to be strong yet flexible. balanced: A three wire circuit that includes two signal lines in opposite polarity and a common shield. Balanced wires are typically utilized with balanced differential circuits which allow the main signal to pass through, while eliminating any external noise which has been generated outside the signal line and is therefore common to both. beat: A resultant frequency which is audible when two tones of similar frequency are added together either electrically or acoustically. biamplification: The use of two separate amplifiers (or two separate channels of a stereo amplifier) to power the high and low frequency drivers of a loudspeaker system. Such a system utilizes a low-level crossover network to separate out the frequency components of the signal before amplification. bias: A high frequency audio signal applied at the record head of a tape recorder to ensure a linear transfer relationship between record and playback. bit: In digital systems, a unit of resolution or clarity. Each bit relates to the binary states of on or off, often designated by the values "1" or "0". Each bit therefore gives two logical or numeric choices. A two bit system gives 2 x 2 choices, a three bit system 2 x 2 x 2 choices and so on. Digital audio systems in use today use a variety of bit rates, from 8 bit (poor quality), through 12 or 13 bit rates (ADAT, Video-8), 16 bit rates (Compact Disc), to 24 bit professional recorders. byte: A digital word 8 bits long.
cancellation: Partial or total loss of signal due to addition of two similar frequencies of opposite phase, either electrically or acoustically. capacitance: The ability of electrical surfaces to store a static charge. Within electronic components, charges present in a conductor attract opposite charges to nearby, but not electrically connected, conductors, thus acting to smooth out, or tune, various signals. Since a material’s capacitance varies over distance, this property can be used in microphones where sound pressure variance moves one element of the diaphragm in relation to another, thus creating an analog signal. Capacitance acts against us over long cable runs where a signal may fade itself away, due to the proximity of the cable’s component wires. capstan: Drive spindle of a tape recorder. In conjunction with the pinch roller, this pulls the tape past the heads at a constant speed, irrespective of the spool size, or how much tape is on each reel in relation to the other reel. Minor variations in motor speed, and eccentricities of the spindle itself, can lead to audible pitch changes (either playback or record !) which are called wow and flutter, depending on their size and effect. capsule: The name given to the head assembly of a microphone which houses and supports the diaphragm. CCIR: In tape recording, one of the various eq standards used to counteract the 6 dB per octave rise at the playback head. Stands for Comité Consultatif International des Radiocommunications, which is obviously European in origin. Others include DIN (Deutsche Industrie Norm), NAB (National Association of Broadcasters), IEC (International Electronics Commission). coating: The recording medium, attached to the backing, onto which we record our signal. cochlea: The snail shaped canal of the inner ear. The cochlea serves to register, and transfer (through the energy generated by the cochlea’s hair cells) the sounds received by the ear, transforming them into electrical impulses that can be received by the brain. common mode rejection: The process by which the signal on a balanced line is passed through an input circuit, while rejecting any spurious signal noise.
compression: (1) In audio theory, the part of a sound wave cycle in which the air particles set in motion by a sound .source are pushed together (with loudspeakers, this is caused by the forward movement of the speaker cone); (2) In audio electronics, the process of reducing the dynamic range of an audio program, usually by a ratio of less than 10:1 (see "limiter"); (3) In digital systems, a mathematical process that reduces the amount of storage space required by data. critical distance: In an enclosed space, the point where the SPL from the direct sound at the source equals the SPL of the reverberant field. crosstalk: The imposition of signal from one channel, track, or circuit onto another so as to interfere with the integrity of the signal on the second channel. current: The flow, or rate of flow, of an electric current in a conductor. Expressed in amperes (amps). cycle: One complete period of a sound (or electrical) wave, encompassing both compression and rarefaction damping factor: Calculated by dividing a loudspeaker’s rated load impedance by an amplifier’s source impedance, the damping factor represents the ability of an amplifier to control undesirable speaker cone motion when no signal is present. The higher the damping factor, the more effective the amplifier will be at controlling the speaker movement and the tighter the subsequent sound. When calculating damping factor it is necessary to include (as part of the source impedance) the impedance of the wire connecting the amplifier with the loudspeaker. DAT: Digital audio tape, and its associated format. Currently three frame speeds in use: 32,000 Hz, which conforms with the international broadcast standard to reproduce a maximum high frequency response of 15 kHz (I’ve never seen anyone use this setting); 44,100 Hz, which corresponds with the compact disc format; 48,000 Hz, which most recording studios use because they think it gives a better quality sound (this frame speed was only ever developed to assist those users who needed to lock their recorders to videotape machines for TV and film post-production work, where some speed variance was to be expected. A maximum of 10 percent was envisaged, which would bring a 44,100 Hz frame rate down to around 39,000 Hz, thus reducing the machine’s ability to reproduce an audio frequency of 20 kHz. 48,000 Hz, played 10 percent slow would be able to reproduce 20 kHz. Two word lengths were envisioned, 16 bit for high quality, normal play, and 12 bit for reduced quality, long play.
dead A subjective term used to describe an environment, or sound, lacking a reverberant quality, or life. decibel (dB): The most common unit of measurement in audio, dB is a logarithmic power ratio that must be referenced to a specific value. The value which 0 dB is referenced to depends on the type of dB calculation being done. dB SPL: 0dB SPL (Sound Pressure Level) is referenced to .0002 dynes/square centimeter, and represents the human threshold of hearing. The threshold of pain for human hearing is somewhere around 120 to130 dB SPL. dB(A): An SPL reading made with the A "weighted" scale, which simulates the response of the human ear when listening at a level of 40 phons. dB(B): An SPL reading made with the B "weighted" scale, which simulates the response of the human ear when listening at a level of 70 - 90 phons. dB©: An SPL reading made with the C "weighted" scale, which is essentially a reading without additional filters. dBm: An electrical power measurement, referenced to 1 milliwatt (the power measured when 0.775 volts is applied to a 600 ohm load. dBu: A measurement of electrical voltage (electrical potential) reference to 0.775 volts. dBV (note the upper case "V"): Another voltage measurement, referenced to 1 volt. dBv (note the lower case "v"): A measurement designed to replace dBu. Also referenced to 0.775 volts. dBW: An electrical measurement of power established to deal with higher power levels. dBW is referenced to 1 Watt. decay time: the amount of time it takes for the acoustical energy (caused by the reflection of sound waves) in a room to drop 60 dB SPL. Also known as the reverberation time. de-Gauss: Over long periods of time, magnetic transducers. Like the head on tape machines, build up a residual magnetic charge, which leads to a poor transfer of magnetic information onto or off tape. The process of de-Gaussing is used to remove this residual magnetic artifact.
digital: A method of sound reproduction utilizing binary code (ones and zeroes, or on/off signals) to sample and reproduce the frequency and amplitude of a sound wave. dispersion: The angle(s) along which sound waves are generated from a loudspeaker, or cluster of loudspeakers. distortion: Much-mentioned, but rarely defined, distortion takes many forms. At its simplest, it is any unwanted alteration to our signal. "Harmonic distortion" comes about through the flattening of peaks in an analog signal, and is generally acceptable unless it is very severe. In fact, a small amount of harmonic distortion can lead to a "warm", and less clinically accurate sound. Some recording engineers use the upper curve of the hysteresis loop (that is, they record at high level, up towards saturation) as a way of creating a mild distortion, especially on guitar sounds. "Inter-modulation distortion", however, can be really nasty. This comes about when two or more signals interact (add and subtract) to produce new and harmonically unrelated frequencies in the signal. Such distortion is often the result of poor equipment design or alignment. Doppler effect: A shift in the pitch of a sound as it moves toward, and/or away from, the listener. A sound moving towards a listener will shift up in pitch as the sound waves are pushed closer together (the wavelength is shortened). A sound moving away from the listener will shift down in pitch as the sound waves are stretched further apart (the wavelength is increased). Doppler also effects electromagnetic waves the same way. Dry: See dead. dynamic range: The difference between the softest and loudest portion of any given program. Dynamic range can be expressed both acoustically (the difference in the level at the microphones), and electrically (the difference at the loudspeakers). EAD: (effective acoustic distance): The perceived rather than the actual, distance between the sound source (a speaker or performer) and the receiver (audience). earth loop: Where several pieces of equipment are linked together, but are powered by electrical sockets of geographically different earthing, a hum may invade the system, as a result of the beating of power sources. Where possible, ensure that all audio devices are powered from one source ! elasticity: The ability of a material to spring back to its original size, shape or position after being expanded or compressed. EMF (electro-motive force): The electrical potential of a circuit (voltage), expressed in volts.
equalization: Originally the addition of a range of frequencies to compensate for high frequency losses which accompany extremely long cable runs (like New York to San Francisco), now used to describe the process of adjusting a signal’s tonal structure. erasure: The process of wiping a tape clean prior to recording something new on it. extinction frequency: The limit of high frequency response of a tape system due to both positive and negative elements of a frequency being present at the replay head, and thus canceling each other out. Affected by tape speed and/or head gap width. feedback: The addition of some or all of a signal back upon itself, thus adding to itself over and over until the gain has increased beyond the system’s limits. filter: An electronic circuit that is used to separate one part of the audio spectrum from other parts. Such filters are utilized in eq circuits, crossovers, and by themselves as "brick wall" filters for eliminating certain frequencies (ie: high pass and low pass filters). flanging: An effect produced by additions and subtractions moving across the audio frequency range. Originally produced by playing the same signal back simultaneously off two tape recorders, then applying pressure with the finger to one of the flange of reel on one machine, thus momentarily slowing it down in relation to the other. These days it is produced electronically. Fletcher/Munsen curves: Graphs compiled by Fletcher and Munsen a long time ago which show the ear/brain’s changing sensitivity to various frequencies according to sound pressure level. flutter: Rapid fluctuation in pitch, a warbling effect, most often found in tape systems, brought about by mechanical irregularities such as eccentricities in the flywheel or spindle. foley: The process of crating (usually human) sound effects in film post production. free-field: A sound field in which the effect of the boundaries is nonexistent (or at least quite minimal). frequency range: The width (from lowest frequency to highest frequency) of the frequency band which a given device (microphone, mixer, amplifier, etc.) will effectively operate within.
frequency response: The measured (within a stated range of dB) effectiveness of the sonic reproduction of a given piece of equipment within its applicable frequency range. frequency: The number of wave cycles that pass a given point during a one second interval. When dealing with sound waves, frequency corresponds to pitch. Measured in hertz (Hz). fundamental: The foundational tone of a given sound. A sound made up of only the fundamental would be represented by a pure sine wave (a rarity in the real world). Most musical sounds are comprised of the fundamental tone plus several harmonic multiples of that tone. gain: The amount (usually specified in dB) that a signal is increased. Most often, "gain" refers to the amount of signal increase provided by a power amplifier. gap width: The distance between the poles of the magnetic recording (or replay or erase) head at the point at which it comes into contact with the tape. gate: A serial signal processor which cuts off or allows through signals of a (usually) user-controlled threshold, or some sort of external control or trigger. Sometimes called a noise gate, or keyed gate. graphic equalizer: An equalizer having a series of filters at set frequencies, each of which has a sliding control mounted on the unit’s front panel - in this manner, the eq curve applied is graphically demonstrated. group fader: Otherwise known as a sub-master fader. A fader on a mixing console to which the outputs of several other faders are fed, or grouped together. harmonics: Integer (related by whole numbers) multiples of a fundamental frequency. The signature sound of a musical instrument is made up of the fundamental tone, plus a specific group of harmonic tones. Such tones are derived from the nature of the material and construction of the instrument. Also referred to as "overtones". Haas effect: The theory that states that a "secondary" sound that is heard within approximately 45 msec. of the original sound will he heard by the receiver as part of the original sound. Where the sound is heard from two loudspeakers (e.g., stereo), and there is a time delay as a result of one speaker being closer to the hearer than the other, all sound will seem to come from the closer speaker. The effect grows rapidly to a maximum as the delay increases to 4-5 msecs (equivalent to a path difference of 1.5 m), and an increase in SPL (Sound Pressure Level) of around 10 dB may be required at the further speaker to recentre the image.
headroom: The electrical difference between the nominal (that is optimum) and peak (that is maximum before distortion) levels of an audio program. Hertz (Hz): The internationally recognized unit of measurement for frequency, originally referred to as "cycles per second". hiss: High frequency noise. hum: Low frequency noise. impedance: The amount of opposition exerted on an alternating current of a single frequency. Measured in ohms, it is a combination of resistance and reactance inductance: The property by which an electrical circuit with a varying current (AC) will produce a varying magnetic field that will induce a counter voltage in itself, or spurious voltages in nearby circuits. Within a single circuit, inductance (the amount of counter voltage created in a circuit) is an aspect of reactance (an integral component of impedance). In a group of circuits, inductance is the characteristic that produces spurious noise voltages and crosstalk. inertia: A principle of physics which describes the tendency of any body of matter at rest, to remain at rest, and if in motion, to remain in motion unless acted upon by some outside force. Gravity, and resistance are two "outside forces" which act upon a body in motion. integer: A whole number (i.e.: 1, 2, 3, 4, etc.). Harmonics are integer multiples of the fundamental tone. Inverse Square Law: The principle that sound pressure level decreases in inverse proportion to the distance from the sound source. With each doubling of the distance from the sound source, SPL will drop by 6 dB. lavalier: the name given to a clip-on, or neck-tie mic. leader: In the audio world, usually opaque backing tape without the magnetic coating used as a spacer between tracks on an audio tape. A very useful visual reference to the start or end of a track. In the olden days, info about the tape’s specifications and other stuff would be written on the leader, in chinagraph pencil. Some leader was purposefully translucent - see stop-light recorders… limiter: A compressor used to prevent a signal from overloading a system or part of a system. While there is no bible on this, a compression ratio of 10:1 or greater is generally considered to be "limiting". line: A path for an electrical signal - at its simplest, a pair of wires.
line level: A signal of high electrical level. Referenced to one of several standards (see "decibel"), and therefore may have a range of values according to what sort of equipment you are using, but generally 50-70 dB above the output of a microphone. live angle: Refers to the angle within which a reasonable frequency response may be achieved by a specific directional microphone. A sound source within the live angle is said to be "on mic", whereas one outside of it is said to be "off mic". load impedance: The impedance value at the input of a connection between two audio devices. This is the impedance "seen" by the output. M and E: A style of mixing which can be used in virtually any program where an "international" version is required. Literally meaning "music and effects", whatever commentary would be on the full mix is omitted, leaving the foreign language to be overdubbed without conflict. meter: A meter is a device which gives the operator a visual point of reference regarding the level of a signal, but all meters are not created equal. You are used to reading VU meters, which give a reading in "volume units". Volume units are approximations of how the ear hears sound - the ear cannot react to rapid changes in level, and consequently you the listener cannot hear transients which can overload sensitive systems. Your ears average out rapid fluctuations in SPL to a continuous level, and that is what a VU meter shows. An alternative is the PPM, or peak power meter, which accurately shows the peak value of the signal’s modulation. This is crucial for avoiding clipping in (for instance) digital audio where even the slightest over modulation can mean disaster. Both VU and PPM meters may come in needle and LED versions, and in good professional equipment, a meter’s ballistics may be switchable from VU to PPM. The more modern trend is for VU meters with peak-hold LEDs, which show VU readings alongside peak values. Both needle and LED readouts are giving way to plasma meters. modulation (signal’s amplitude) : No amplitude means no signal which means no modulation, whereas the maximum amplitude prior to distortion means 100% modulation. Clipping means over modulation. moving coil: Relates to phonogram cartridges and microphone capsules which rely on a coil of wire moving (modulating) within a magnetic field, thus leading to the induction of an analog signal. nibble: Half a byte ! nodes: The low SPL point of a standing wave, corresponding to the trough of the related wave form.
noise floor: The softest level of an audio program, it includes the basic level of the acoustical and electronic background noise in an audio (and electronic) environment. Nyquist theorem: A theorem that establishes a relationship between frame (or sample) rate and the highest frequency reproducible in digital audio systems. Essentially, the sample rate must be at least twice the highest frequency reproducible. PCM: Pulse code modulation, and early name for digital audio signals. pad: Usually found on mixers, an attenuator(electronic component) of fixed value, useful in decreasing the strength of a signal. pan control: A knob on a mixing console which can direct a mono signal from all the way to the left (odd numbered groups), to all the way to the right (even numbered groups), or anywhere in between, in a stereo mix. Has other uses, especially in M and E mixes. peak: The loudest level of an audio program. phantom power: A power source that feeds a condenser microphone’s amplifier circuits by way of an electrical connection along the of live signal wires of a balanced microphone line. perspective: The concept that action that looks like its a long way away should sound like that too. Achieved by various means - an actor moving from on-mic to off-mic while talking may be perceived as moving away from the listener. An actor furthest from the camera may be on-mic, but looser (that is, further away from it), the effect of distance coming about through a reduced level, plus an increased percentage of "room" reverberation. phase: The position of two sound waves relative to each other. The effect one wave has on another is related to their respective phase relationship. phon: A measurement of apparent loudness based on the Fletcher-Munson curves. A phon represents the response of the ear to a 1 kHz tone. piezoelectric: A material which generates an electrical voltage when bent or twisted. Such material is used as the transduction element in piezoelectric speaker drivers, as well as in some small and inexpensive microphones. photoelectric cell: A light-sensitive element that emits an electric charge when light hits it. The electric charge can be used to switch things on or off.
pinna: The outer flap of the ear, it serves to collect sound and hold up your hat. polar pattern: A microphone’s sensitivity in relation to direction. Cardioid, hypercardioid, supercardioid, omni-directional, figure of eight are all polar patterns. popping: Over modulation due to an over extension of a microphone’s diaphragm, usually associated with various voice elements, like the letter "p" and "b", and usually resulting in an excess of low frequency during that element. Other letter sounds can create similar artifacts in your signal - the letter "f" can result in a particular artifact called "phutting". pre-emphasis: The equalization of a signal (usually the boosting of high frequencies) to make better use of the characteristics of certain transmission mediums. Accompanied by an equivalent de-emphasis on playback/reception. presence: The quality of a voice or instrument that makes it sound louder, clearer or closer than its electrical level would suggest. Often achieved through the boosting of the mid-range, there is no guarantee of success. Some voices possess this quality naturally. pressure gradient microphone: Capsule construction that allows sound to reach both the front and the back of a diaphragm, which therefore responds to the difference (or gradient) in sound pressure between these faces. A very important component in the design of directional microphones. pressure microphone: Capsule construction that has only one side of the diaphragm open to sound pressure, and thus responding only to fluctuations in air pressure, no matter from which direction they arrive. An omni-directional microphone. print-through: The tendency for a magnetic field to bleed through the backing of tape while tightly wound on the spool and so imprinting the sound from one area of the tape onto another, so tapes which are to be left on the shelf are often left "tail out", that is with the end of the tape, not the start of the tape, on the outermost part of the reel. This doesn’t stop print-through, but merely moves it to a part of the tape where program already exists, and this masks its effects. proximity effect: The natural tendency of some microphones (most notably cardioid patterns) to demonstrate a boost of the low frequencies when placed close to the sound source. Also known as "bass tip-up". Q: In parametric equalizers, the ratio of the center frequency to bandwidth. The higher the Q number (most commonly between 1 and 5), the narrower the bandwidth.
rarefaction: The part of the sound wave cycle in which the air particles set in motion by a sound source move further apart (with loudspeakers, this is caused by the backward movement of the speaker cone). reactance: A frequency based resistance to current caused by inductance. Reactance combined with resistance make up the impedance of an AC circuit. reflection: A sound wave that has bounced off of at least one surface. It can also refer to the digital replication of such a sound wave in a digital effects unit. resistance: The amount of opposition a conducting material exerts on the flow of current. in a DC circuit. Expressed in ohms. resonance: The property of materials or acoustic spaces to vibrate at particular frequencies, and not at others. reverberation time:(RT 60): The amount of time it takes for the acoustical energy (caused by the reflection of sound waves) in a room to drop 60 dB SPL. Also known as decay time. reverberation: The overall sound created by multiple reflections of sound waves in a room or artificially created environment. SCR (silicon controlled rectifier) noise: An evil noise that invades the power supply (and therefore your otherwise beautifully clean signal) when the lighting department fade their lights up and down. SCRs are lighting dimmers which control the amount of electricity each bubble gets per cycle of the AC power supply by chopping out massive segments of the electrical waveform. Old and cheap. Where possible, always use one phase of a three phase power supply not being used by those further down the food chain. sabine: The unit of measurement of sound absorption. Rated from 0 to 1. 1 sabine represents an open window (reflecting no sound), while 0 represents a perfectly reflecting surface with no absorption. sensitivity: A microphone specification which rates the output signal (in either dBV or dBm) of a given microphone when subjected to a specified sound pressure level at the front of the mic (either 74 dB SPL, or 94 dB SPL). As a loudspeaker specification, sensitivity relates to the level (in dB SPL) that the loudspeaker will generate at a distance of 1 meter (on axis) from the speaker when 1 watt of power is fed to it. signal: The electrical current that emulates the sound that created it.
signal to noise ratio: The difference between your signal and the noise inherent within the system that carries it, measured in decibels. Audio heaven is achieved when the s/n ratio is massive - the CD system ,claims a whopping 98 dB; TV claims around 60 dB; vinyl somewhere around 55 dB. sine wave: The most basic wave of a pure audio tone. More complex wave forms are made up of combinations of sine waves. source impedance: The impedance value at the output of a connection between two audio devices. spill: Unwanted sound getting into your microphone from a loud or close sound source, thus reducing separation. standing waves: Sound waves reflecting from parallel walls that combine to set up areas of high and low pressure points (corresponding with the peaks and troughs of the waveform) known as nodes and antinodes. stapedes muscles: Tiny muscles in the inner ear that serve to "damp down" high SPL sounds, by stiffening the bone linkages of the middle ear, thereby limiting the energy transfer of excessive (and damaging) amounts of sound energy. stop light recorders: Audio tape recorders which utilize a photoelectric cell in conjunction with a small bulb to stop the tape transport. A translucent leader would be inserted between tracks, and when a track had finished playing, or when the machine was put into spool mode, the bulb would shine through the leader and excite the photoelectric cell, thus enacting an electrical switch that would turn off the transport mechanism. talkback: A circuit that allows the mixing engineer to speak to those on stage, or in a recording studio, by routing of a microphone signal from the mixing board through the monitor system. time code: An electronic time signal which may be recorded and displayed. It is usually referenced to a film or video picture where every frame is numbered in sequence. Crucial for editing and synchronizing picture to picture, or picture to sound for editing purposes. There is a time code for each and every type of video and film frame rate, and these are defined by a joint SMPTE/EBU standard (Society of Moving Picture and Television Engineers/European Broadcast Union). MIDI machine control is a form of time code, as is MIDI show control, but these are sync clocks usually used in music production or the timing of staging effects in the theatre, and are not necessarily associated with picture frames.
transducer: A device that changes one form of energy into another. "Electrostatic" transducers transform acoustic energy (the energy form sound waves) into electrical energy (and vice versa). transduction: The conversion of one form of energy into another. transient: The very rapid peak of a sound, usually associated with its moment of creation. No matter what your VU meter tells you, this very short-lived sound was very loud, and you probably couldn’t catch it without some sort of distortion due to clipping. transient response: The measurement of a component’s ability to accurately respond to rapid peaks (such as a drum rimshot, or stacatto piano strike) within a sound program. TRS: Short for tip-ring-sleeve, and referring to a ¼" (6.5 mm) plug and/or jack with two channels (one at the tip, and one at the ring), plus a ground connection (at the sleeve). Stereo headphones also use this type of plug. velocity of sound: In air at room temperature this is approximately 1120 ft/sec (340 m/sec). It can be calculated rough as 1087 + 2T ft/sec, where T is the temperature in degrees Celsius. Humidity makes a slight difference: in fully saturated damp air it is 3 ft/sec faster than in dry air. In liquids and solids it is much faster than in air. Altitude - the density of air - makes a difference, too. voltage: The electrical potential or electro-motive force (EMF) of a circuit. Expressed in volts. wavelength: The physical length of one cycle of a sound wave. The higher the frequency of a wave, the shorter its wavelength. weighted: Particular ways of referencing a signal level (or hum or noise) due to the ear’s ability to discriminate against certain frequencies, especially low frequencies, at different SPLs. See Fletcher/Munsen. word length: In digital systems, the resolution of each sample measured in bits. wow: Like flutter but at much lower frequencies
