Helical and 145 Other Audio Terms You May Need to Know
Yes, this is a helical antenna – Big brother to the "rubber ducky" antenna on yesterday's mobile phones[/caption]Helical? This could describe a bad day in the studio or a buzzing sound that just won't go away. Fact is, it's a type of a directional antenna that might be the answer to getting better performance from your wireless systems. In this post, Shure Notes Editors have searched the archives for terms that you're likely to encounter in your audio explorations.
If all you need is a quick definition of an audio term or acronym as you peruse a tech sheet or user's guide, just bookmark this post and find it right here.
3-to-1 Rule – When using multiple microphones, the distance between microphones should be at least 3 times the distance from each microphone to its intended sound source.
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3-1 Rule[/caption]Absorption – The weakening of radio wave strength by losses in various materials.
ADC – Analog-to-digital converter, also abbreviated A/D.
Ambience – Room acoustics or natural reverberation.
Ambient Sound – Local or background sounds.
Amplitude – Magnitude of strength of signal or wave.
AM Rejection – Ability of an FM receiver to reject signals from AM transmitters and/or AM noise from electrical devices or natural sources.
Antenna – Electrical circuit element that transmits or receives radio waves.
Antenna Gain – Measure of antenna efficiency compared to a reference antenna, for example: dBi = gain relative to theoretical isotropic (spherical omnidirectional) antenna.
Antenna Splitter – A device for electrically matching a single antenna to multiple receivers.
Attenuation – Measure of the loss of amplitude of a signal.
Automatic Mixer – A specialized mixer that turns off unused microphone channels without any user intervention, and turns on microphone channels as needed.
Auxiliary (Aux) Send – An extra output from a mixer channel with separate level control. Usually used to create monitor mixes or as effects sends.
Bandwidth – A measure of the frequency range of a signal or device.
Base Frequency – The actual frequency of a crystal oscillator, usually then multiplied to some higher operating frequency.
Bias Voltage – A fixed DC voltage that establishes the operating characteristic of a circuit element such as a transistor.
Bit – Smallest digital data element, has a value of "0" or "1".
Bodypack – Transmitter style that can be worn on the body.
Boundary/Surface Microphone – A microphone designed to be mounted on an acoustically reflective surface.
Capture – The effect of a strong FM signal suppressing weaker signals at the receiver.
Cardioid Microphone – A unidirectional microphone with moderately wide front pickup (131 degrees). Angle of best rejection is 180 degrees from the front of the microphone, that is, directly at the rear.
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Cardioid Polar Pattern[/caption]Carrier – The basic or unmodulated radio wave.
Cascade – Active antenna output port of receiver or antenna splitter than can feed another receiver or antenna splitter.
Close Pickup – Microphone placement within 2 feet of a sound source.
Comb filtering – the variations in frequency response caused when a single sound source travels multiple paths to the listener's ear, causing a "hollow" sound quality. The resultant frequency response graph resembles a comb. Can also occur electronically with multiple microphone picking up the same sound source.
Codec – Software algorithm for data compression and decompression (code-decode).
Compander - A two-step noise reduction system consisting of a compressor in the transmitter and an expander in the receiver.
Compressor – A device that controls varying signal levels.
Condenser Microphone – A microphone that generates an electrical signal when waves vary the spacing between two charged surfaces: the diaphragm and the backplate.
DAC – Digital-to-analog converter, also abbreviated D/A.
dBm – Ratio of power levels relative to one milliwatt, for example: 0dBm = 1mW, 10dBm = 10mW.
Decibel (dB) – A number used to express relative output sensitivity. It is a logarithmic ratio.
DECT – Digital Enhanced Cordless Telecommunications, standard for digital cordless telephones, for example: 1920-1930 MHz in the US, different bands in other countries.
Demodulation – The recovery of the original modulating information from a radio signal.
Detector – The circuitry that performs demodulation.
Delay (echo) – Reflection of sound that is delayed long enough to be heard as a distinct repetition of the original sound.
Deviation – The maximum frequency variation of an FM signal.
Diffraction – The bending or partial reflection of radio waves by metal objects.
Dipole – An antenna that is made up of two active elements.
Direct – Not reflected.
Distortion – Any unwanted difference between the original and final version of a signal.
Diversity – Receiver design that picks up a radio signal simultaneously at multiple locations and intelligently switches or combines to yield the best continuous signal.
Dropout – The complete loss of received signal due to multipath interference.
DSP – Digital Signal Processor, used in digital and hybrid radio circuits.
Dynamic Range – Maximum amplitude range of a signal or device, generally the difference between the strongest and weakest signals that occur or that the device can handle.
Echo – Time delay of an audio signal that is long enough (typically more than 20 milliseconds) to be heard as a distinct repetition of the original sound.
Electret – A material (such as Teflon) that can retain a permanent electric charge.
Encryption – Encoding a transmitted signal so that it can be decoded only with a unique digital "key".
EM – Electromagnetic.
EQ – Equalization or tone control to shape frequency response in some desired way.
Equalizer – A signal processor that allows the user to boost or cut selected frequencies. Used for tone shaping and limited feedback control. Variations include graphic or parametric.
Expander – A circuit that expands the dynamic range of a signal by a finite ratio, typically 1:2 in a compander system.
Fading – Loss of signal strength due to distance or obstacles in the signal path.
FCC – Federal Communications Commission, US radio regulatory agency.
Feedback – In a PA system consisting of a microphone, amplifier, and loudspeaker, feedback is the ringing or howling sound caused by amplified sound from the loudspeaker entering the microphone and being re-amplified.
Fidelity – A subjective term that refers to perceived sound quality.
Field – A distribution of energy in space, for example: electric, magnetic, sound.
Flat Response – A frequency response that is uniform and equal at all frequencies.
Frequency – The rate of repetition of a cyclic phenomenon such as a sound wave. Usually measured in Hertz (Hz).
Frequency Agile – Having the ability to change frequencies: tuneable.
Frequency Diversity – Scheme that relies on statistical decorrelation of the same signal transmitted and received at multiple frequencies to minimize RF interference effects.
Frequency Hopping – Spread spectrum technique using continuous, synchronized frequency changes across a wide frequency range.
Frequency Response – Variation in amplitude of a signal over a range of frequencies.
Front End – Initial filter stage of a receiver when sound waves cause a conductor to vibrate in a magnetic field. In a moving-coil microphone, the conductor is a coil of wire attached to the diaphragm.
Gain – Amplification of sound level or voltage.
Gain-Before-Feedback – The amount of gain that can be achieved in a sound system before feedback or ringing occurs.
Geolocation – Ability of a TVBD to determine its geographic location.
Ground Plane – Electrical approximation of a zero-potential reflective surface at the base of an antenna.
GSM – Global Systems for Mobile Communications, mobile telephone standard, for example: 850 Mz and 1900 MHz in the US, different bands in other countries.
Handheld – Transmitter type that can be held in the hand.
Headworn Microphone – A microphone that is worn on the head.
Helical – Wideband directional antenna consisting of a single circularly-polarized element.
Hertz (Hz) – A unit of measurement that represents cycles-per-second. The musical note "A" above middle "C" is equivalent to 440 Hz.
Hybrid – Radio design combining digital audio processing with analog transmission.
IEM – In-ear monitor.
IFB – Interruptible fold back, a cueing system used in broadcast.
IM – Intermodulation, frequencies produced by combinations of other frequencies in non-linear devices.
IMD – Intermodulation distortion (another name for IM).
IM Rejection – Ability of a receiver to reject IM products.
Impedance – In an electrical circuit, opposition to current flow of alternating current, measured in ohms. A high impedance microphone has an impedance of 10,000 ohms or more. A low impedance microphone has an impedance of 50 to 600 ohms.
Interface – Typically refers to a device that converts analog audio signals to a digital signal for connection to a personal computer, and vice versa. Digital audio interfaces can either be internal (on a PCI card) or external (with a USB or Firewire connection to the computer).
Indirect – Reflected or diffracted.
Inverse Square Law – Mathematical relationship in which one quantity is inversely proportional to the square of another quantity, for example: signal strength decreases according to the distance squared.
Isolation – Freedom from leakage; ability to reject unwanted sound.
Latency – A delay between the time that an audio signal is converted from analog to digital, processed, and transmitted, and the time that it is heard by the listener. Latency can very greatly depending on the software and file format used. Typical latency for audio ranges from a few milliseconds to over 100 milliseconds (1/10th of a second). If the delayed audio signal being is compared to an undelayed signal (such as a performer hearing his or her own voice) or to an undelayed visual reference (such as an audience member seeing the image of a live performer), delays of more than a few milliseconds can be noticeable to the listener.
Lavalier Microphone – A small microphone designed for hands-free usage. Usually clipped to the clothing.
Leakage – Pickup of an instrument by a microphone intended to pick up another instrument.
Level – The amplitude or strength of a signal.
Limiter – A circuit that limits the maximum level of a signal.
Line-of-sight – Preferred wireless operating condition where the transmit antenna is visible to receive antenna with no obstruction.
Log Periodic – Wideband directional antenna consisting of multiple logarithmic-spaced dipole elements.
Loss – Decrease in signal strength during transmission, propagation or reception.
Medium – Substance through which a wave propagates; for radio it may be vacuum, gas, liquid or solid; wave speed is affected by medium.
MP3 – The most popular format for compressed audio files. When an MP3 file is created, the encoding software discards some of the data that is deemed to be unnecessary or redundant. The more data that is discarded, the smaller the file size but the lower the sound quality. MP3 is an acronym for MPEG3, which is itself an abbreviation.
Multitrack Recording – A method of recording where each instrument (or group of instruments) is recorded onto a separate track and later combined into a stereo mix. Common formats include 4, 8, 16, and 24-track recording.
Noise – Unwanted electrical or acoustic interference.
Omnidirectional Microphone – A microphone that picks up sound equally well from all directions.
Overhead Microphone – Microphones that are typically hung from the ceiling. Common applications are choir and theater miking.
PA – Public Address. Usually refers to a sound reinforcement system.
PAG – Potential Acoustic Gain is the calculated gain that a sound system can achieve at or just below the point of feedback.
Phantom Power – A method of providing power to the electronics of a condenser microphone through the microphone cable.
Polar Pattern (Directional Pattern, Polar Response) – A graph showing how the sensitivity of a microphone varies with the angle of the sound source, at a particular frequency. Examples of polar patterns are unidirectional and omnidirectional.
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KSM42 with a Pop Filter[/caption]Pop Filter – A screen, typically made of nylon or other tightly-woven mesh, designed to prevent plosives (loud, low frequency thumps caused by the consonants "p" and "t") from reaching the microphone.
Power – Usually refers to the RF power delivered to the transmitter antenna, measured in milliwatts (mW).
Propagation – Ability of radio signal to travel a significant distance.
Protected Channels – Designated TVBD-free TV channels at a given location, defined by FCC rules.
Proximity Effect – The increase in bass occurring with most unidirectional microphones when they are placed close to an instrument or vocalist (within 1 ft.). Does not occur with omnidirectional microphones.
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Proximity Effect Graph[/caption]Radio Waves – Electromagnetic waves that propagate a significant distance from the source.
RCV – Abbreviation for Receiver.
Receiver – Device that is sensitive to radio signals and recovers information from them.
Reciprocal – Property of a passive antenna to operate equivalently either in transmit or in receive mode.
Reflection – Retransmission of incident radio waves by metal objects.
Reverberation – The reflection of a sound a sufficient number of times that it becomes non-directional and persists for some time after the source has stopped. The amount of reverberation depends of the relative amount of sound reflection and absorption in the room.
RF – Radio frequency, generally taken to mean well above 20,000 Hz.
RFI – Radio frequency interference.
Ribbon Microphone – a dynamic microphone that incorporates a metal ribbon suspended in a magnetic field. Shure's KSM313 and KSM353 mics are ribbon mics.
Rolloff – A gradual decrease in response below or above some specified frequency.
Sampling – Conversion of a continuous audio waveform into discrete digital values.
Selectivity – Measure of a receiver's ability to discriminate between closely-spaced frequencies.
Sensitivity – The electrical output that a microphone produces for a given sound pressure level.
Shadow – Blocking of radio waves by reflective or absorptive (lossy) objects.
Shaped Response – A frequency response that exhibits significant variation from flat within its range. It is usually designed to enhance the sound for a particular application.
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Shaped Frequency Response[/caption]Shock Mount – A suspension system for mounting a microphone that reduces pickup of unwanted low frequency sounds caused by mechanical vibration.
Shotgun Microphone – An extremely directional microphone, commonly used in broadcast and film production applications.
Signal Processor – Any device or software plug-in that can manipulate the audio signal, in terms of level, frequency, time, or phase. Examples of signal processors include equalizers, compressors, delay (echo), and reverb. Signal processors can be used to correct problems with an audio signal, or for creative effect.
Signal-to-Noise Ratio – Overall useable amplitude range of a signal or device, generally the difference between some reference level and the residual noise level.
Sound Reinforcement – Amplification of live sound sources.
Squelch – Circuit in a receiver that mutes the audio output in the absence of the desired transmitter signal.
Spectrum – A range of discrete frequencies.
STL – Studio Transmitter Link, in the US: 944-952 MHz.
Stereo – Two channels of audio, left and right, which can be used to simulate realistic listening environments.
Supercardioid Microphone – A unidirectional microphone with a tighter front pickup angle (115 degrees) than a cardioid, but with some rear pickup. Angle of best rejection is 126 degrees from the front of the microphone, that is, 54 degrees from the rear.
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Supercardioid Polar Pattern[/caption]Transducer – a device that converts one form of energy to another.
Transmitter – Device that converts information to a radio signal.
TVBD – Television Band Device, sometimes called White Space Device.
TX – Abbreviation for transmitter.
UHF – Ultra high frequency (about 300 - 3000 MHz).
Unidirectional Microphone – A microphone that is most sensitive to sound coming from a single direction – in front of the microphone. Cardioid and supercardioid microphones are unidirectional.
USB – An acronym for Universal Serial Bus, a standard designed to allow many different types of devices to connect to a computer using a standardized interface. USB also can provide power to low-consumption devices, negating the need for external power supplies. There are currently two standards: USB 1.1 and USB 2.0.For audio applications, USB 2.0 (which offers much faster data transfer rates) allows many more channels of audio to be streamed to the computer at once.
VCA – Voltage controlled amplifier, used in audio compressor and expander circuits.
VCO – Voltage controlled oscillator, used in radio tuning circuits.
VHF – Very high frequency (about 30 - 300 MHz).
Wavelength – The physical distance between successive complete cycles of a wave, inversely proportional to frequency, dependent on properties of medium.
WAV – A file extension that refers to a standard for storing audio data. Commonly referred to as a WAVE file, it is short for Waveform audio format. The most common WAVE file stores full, uncompressed audio for the highest quality.
White Space – Unoccupied space between active TV channels.
Wideband – An FM signal in which the deviation is much greater than the modulating frequency.
WMA – A proprietary Windows audio file format.
