Pre-amp (Preamp)
Short for ‘pre-amplification’ : an active gain stage used to raise the signal level of a source to a nominal line level. For example, a microphone pre-amp (aka mic preamp).
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Pre-emphasis
A system for applying high frequency boost to a sound before processing. When the corresponding de-emphasis is applied any noise contribution from the processing is reduced.
Proximity Effect
Also known as ‘Bass tip-up’. The proximity effect dramatically increases a microphone’s sensitivity to low frequencies when placed very close to a sound source. It only affects directional microphones — omnidirectional microphones are immune, and the effect can be nullified on a cardioid mic if the close source is placed 90 degrees off-axis.
PWM Compression
A form of audio compressor which uses Pulse Width Modulation to detedmine the energy in the audio signal over time. In essence, the audio signal is sampled at a very high rate, but the duration (width) of the samples (pulses) is adjusted (modulated) to control the average energy over time, and thus provide signal attenuation. When done well, this is the fastest form of compressor with the lowest distortion artefacts.
Q
Q is short for the ‘quality-factor’ of a filter, which defines its bandwidth in relation to its centre frequency and indicates a filter’s resonant properties. The higher the Q the more resonant the filter, and the narrower the range of frequencies that are allowed to pass. A Q of 1 is equivalent to bandwidth of 1.38 octaves, while a Q of 6 is equivalent to a bandwidth of just 0.25 octaves, and a Q of 0.4 is equivalent to a bandwidth of 3 octaves.
RF Capacitor Microphone
An alternative form of capacitor microphone which uses the capacitive capsule as the tuning element of a radio-frequency oscillator. Sound waves arriving at the capsule change its capacitance, which varies the frequency of the RF oscillator to produce an FM signal. This is immediately demodulated by the microphone's internal circuitry to produce the audio output. The advantage of this approach is that the capsule works in a very low-impedance environment (as opposed to the very high-impedance environment of a traditional DC-biased and Electret capacitor mics), making it immune to the effects of humidity which can cause unwanted noise in conventional capacitor mics. This technology was invented by Sennheiser and is used in their MKH range of microphones.
ROM
Read Only Memory — A permanent or non-volatile type of memory chip containing data that can't be changed once programmed. Operating systems are often stored on ROM as the memory remains intact when the power is removed.
Room Modes
Acoustic resonances within an enclosed space or room. These occur at specific frequencies where the source sound is reflected from the room's boundaries to reinforce and/or cancel with itself to create standing waves. This results in some areas in the room with very boomy or exaggerated pitches, and others where the pitch may be almost completely absent. The resonant frequencies involved relate directly to the sound wavelength and room dimensions, and is particularly prevalent at low frequencies.
Sample Rate
The number of times an A/D converter samples the incoming waveform each second. The sample rate must be more than twice the highest frequency to be encoded — according to the Nyquist Theorem.
Scrubbing
A term taken from the practice of editing analogue tape where the tape was manually dragged back and forth across the replay head to locate the required edit point using an action similar to the cleaning action of 'scrubbing'. The term is now routinely used in DAWs and audio editing software platforms where the audio is played forwards or backwards at variable speeds, usually to locate an edit or cue point. A Jog Wheel is often used as the hardware controller for scrubbing.
Sine Wave
The waveform of a pure sinusoidal tone which has a waveform defined by a mathematical function derived from a classic periodic oscillation, such as the movement of the tip of swinging pendulum. In a musical context, a sine wave contains only a single fundamental frequency, and no harmonics.
Sound Card
A dedicated interface to transfer audio signals in and out of a computer. A Sound Card can be installed internally, or connected externally via USB2 or FireWire, and they are available in a wide range of formats, accommodating multiple analogue or digital audio signals (or both) in and out, as well as MIDI data in and out.
S/PDIF
Sony/Philips Digital InterFace. Pronounced either ‘S-peedif’ or ‘Spudif’. A stereo or dual-channel self-clocking digital interfacing standard employed by Sony and Philips in consumer digital hi-fi products. The S/PDIF signal is essentially identical in data format to the professional AES3 interface, and is available as either an unbalanced electrical interface (using phono connectors and 75ohm coaxial cable), or as an optical interface called TOSlink.
Toslink
Shorthand for 'Toshiba Link', an optical audio connection. See S/PDIF.
Triangle Wave
A symmetrical triangular shaped wave containing odd harmonics only, but with a lower harmonic content than the square wave.
TRS Plug
TRS refers to the 3-terminal 'Tip, Ring and Sleeve' format of various types of jack plug, typically used either for stereo unbalanced connections (such as on headphones) or mono balanced connections (such as for line-level signals). A 2-terminal alternative is also available, referred to as the TS (Tip, Sleeve) version, used for mono unbalanced signals. The term is applicable to A-type, mini-jack, B-type, and Bantam connectors.
True Peak Meter
– A form of digital audio meter which is capable of determining the absolute amplitude value of a digital signal by using oversampling to fully reconstruct the waveform.
Truss Rod
A metal bar within a guitar neck which is tensioned so as to counteract the tendency for the neck to bend under the tension of the strings.