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Glossary – I
IC – See “Integrated Circuit.” IM Distortion – See “Intermodulation Distortion.” Imaging –Refers to the ability to localize a specific sound within the sound space. In recording environment, it refers to “placing” instruments within the stereo or surround field so that it when the sound is played through speakers, it fools our ears into thinking the sound source is in emanating from a specific point instead of from the speakers. In live audio and sound reinforcement, the principle of imaging is the same, the goal being to make the audience perceive the sounds as coming from performers on the stage, rather than from the speakers. Impedance – Refers to the resistance of a circuit or device to alternating current, which can be mathematically described as the ratio of voltage to current. Differences in impedance between devices in the studio can affect how they work together. Impedance is abbreviated by the letter Z, and measured in ohms (W). In Phase – The desirable situation in which two or more devices (and their respective audio signals) are on the same side of the polarity spectrum, producing waveforms that do not conflict or cancel each other out. Inductance – A characteristic of electrical conductors in which electrical charge (voltage) is produced or stored magnetically due to the natural resistance to change in the electrical current. Inductance is an electromagnetic principle that can either assist in audio applications (as in loudspeakers) or cause resistance (as in using speaker wire whose gauge is too low for the application). Inductor – A device (usually a coil of wire) that converts electrical energy into stored magnetic energy as electrical current passes through it. Commonly found in a variety of audio applications such as guitar pickups and loudspeakers. In Line Console – An audio mixing console that is designed and configured so each channel strip can be used for both recording and monitoring functions during multitrack recording. This configuration is in contrast to split mixing consoles, which requires separate channels on the board for recording and monitoring functions. In Port – A jack on a MIDI device or computer that will accept an incoming data signal. Infinite Baffle – A loudspeaker mount or enclosure designed so that sound waves coming from the front theoretically do not reach the back, preventing the sound waves from cancelling each other out. The term “infinite” comes from the idea that mounting the speaker on a wall with no end points would not allow sound waves to migrate behind it. Of course, this is physically impossible, so infinite baffles are designed to replicate this as much as possible. Examples of infinite baffles are mounting the speaker on a wall of an enclosed room, or building it inside a sealed cabinet large enough to prevent rear sounds from affecting the cone from the back. Input – The jack or physical location where a device receives a signal. Also refers to the incoming signal itself. Input Impedance – The opposition to current flow by the first circuits of a device. Input Monitoring – A setting on many DAWs that allows you to monitor the live input signal coming into the DAW (as opposed to the recorded signal). Insert – An access in the signal chain (usually in the mixing console or virtually within a DAW) in which a device, signal processor or digital plug-in can be “inserted” into the circuit between pre-amplification and the channel or bus output. Commonly used to add processing such as reverb, compression or EQ to a channel or group of channels. Instrument Amplifier – A device that has a power amplifier and speaker to reproduce the signal put out by an electric instrument. Instrument Out Direct – Feeding the output of an electric instrument (like an electric guitar) directly to the recording console or tape recorder, as opposed to miking the amplifier.. Insulator – A substance such as glass, air, plastic, etc., that will (for all practical purposes) not conduct electricity. Integrated Circuit (Abbreviated “IC”) – A miniature circuit of many components set on semiconductor material, used in electronics. A fancy term for “chip” or “microchip.” Interface – Any device or connection point that allows one unit to work, drive or communicate with another unit, or that allows a human to interact with a computer or other electronics. There are many examples of interfaces in professional audio situations, including MIDI (Musical Instrument Digital Interface); audio interfaces which connect audio inputs to your computer; and even your DAW program, which displays a screen that enables you to assign instruments, adjust settings, record, mix and playback. Even the mixing console is an interface of sorts, connecting the many elements of the control room. Intermodulation Distortion – Distortion caused by two or more audio signals of different frequencies interacting with one another. The sum and difference of the frequencies produce new (usually unwanted frequencies) that didn’t exist in any of the original frequencies. Inverse Square Law – A mathematical rule that describes an inverse relationship between one quantity and the square of another quantity. In plain English, one number goes down by a certain amount each time the other number doubles. In audio and acoustics, the inverse square law says that in an open sound field with no obstructions, the sound pressure level will drop by half (6dB) each time the distance from the sound source is doubled. (This equation is quite useful to audio engineers trying to provide sound in open-air settings, for example.) I/O – An abbreviation for “Input/Output.” In audio, it refers to any device, program or system involving the transferring of electrical/audio signals or data. Isolation – The process of containing sound within a certain area so that it doesn’t interact with other sounds. For example, acoustically treated isolation booths are often used to record vocals or instruments in the studio to keep outside noises from bleeding into the recording microphone, or likewise to keep vocals or other sounds away from instrument mics during live recording sessions.