IDE: An abbreviation for Integrated Drive Electronics, which is a peripheral connection standard used in IBM compatibles and some models of Macintosh. IDE drives have the same spinning disk mechanism as their SCSI counterparts (see WFTD archive SCSI), but use a different electronic interface. IDE has been a less expensive and easier technology to implement over the years. This is one of many reasons why PC's have always been on the lower end of the price curve as compared to Macintosh, which primarily use SCSI drives and have SCCI interface busses built in (SCSI is almost always an upgrade option for a PC). SCSI drives and buss systems generally outperform IDE systems in most tests for speed, especially where extremely large files are used (like in digital audio workstations).
IEC: Abbreviation for the International Engineering Consortium. Founded in 1944, the International Engineering Consortium is a nonprofit, public service organization sponsored by universities and engineering societies dedicated to continuing education for the U.S. electronics industry. They are responsible for organizing and establishing standards that are employed in all sorts of electronic equipment. A couple that are relevant to us are the IEC time code standard used by many DAT machines, and the IEC power cable connection, which is the most common type of removable power cord connector used in our industry.
Image File: An image file is used to store an exact replica of a specific set of data on some type of disk drive or in computer RAM. For example: One might keep an "image" of a particular floppy disk stored on a hard drive so it can be retrieved at a later date. The procedure for retrieval usually involves running some software that recreates the image of the original floppy disk on a new disk. Image files are also frequently used with CD writers to prepare data to be written to a CD. In this case all of the desired files are copied into an "image" of the CD that is on a hard drive. Once ready, this image can quickly be written to the recordable CD. Sometimes this procedure is required in order to be able to write a suitable CD, but this will vary upon the software and hardware being used.
Imaging: The ability to localize a sound in a stereo field or mix is called imaging. Several things will affect the ability of a speaker system to image accurately: How matched the speakers are in construction and level (volume), exactly matched phase, and the interaction of the speakers with the listening environment will all be critical in determining imaging. Assuming that the first items are determined by the speaker manufacturer and your system set up, careful acoustic treatment in your room can often make the largest difference in the clarity, stereo spread, and imaging of your studio monitoring system.
Impedance: Measured in ohms, impedance refers to the resistance of a circuit or device to AC (alternating current). Such an AC circuit could be any two audio devices connected together, like a speaker and an amp, passing audio signals. All other things being equal, more power (watts) will flow through a speaker with a low impedance than one with a high impedance. This will also put a greater strain on the amplifier to try to produce this power. If the impedance is too low your amp will not be able to handle it and bad things will happen. Most modern electronic audio devices have extremely high input impedances so they can be driven by very low power outputs. This is one of many reasons why high quality audio equipment can be built so much less expensively these days.
Impulse: An impulse is a signal or sound that has a very short (vanishingly short) duration. A true mathematical impulse has zero duration and infinite amplitude, but still a finite amount of energy.
Impulse Response: In essence, the way a particular device responds to an impulse. For example, the reverberation of a room can also be thought of as its impulse response. A great deal of information about a device can be determined by how it reacts to an impulse. The frequency response, phase response, and transient response are all tied to this specification, though this specification itself is rarely seen on a spec sheet.
Inductance: The process of storing electrical energy in magnetic fields. An inductor is any element in an electrical circuit having a magnetic field, though usually by design these elements are coils and transformers. When inductance and frequency are considered together, a value of inductive reactance, measured in Ohms, is formed. This reactance looks like resistance to current flow for a signal of a given frequency. Inductive reactance and capacitive reactance together form reactive impedance.
Infantile Failure - (a.k.a. infant failure mode): Refers to the known statistical fact that electronic equipment components are most likely to fail within the first 24 to 48 hours of use. Electronic components typically have very low failure rates in general, but when they do fail, the vast majority of them fail in the first few hours of use. There are a variety of factors that come in to play in the manufacturing and assembly of electronic equipment that can cause instability or even failure during initial power up. Many times components that are "stressed" during initial power up, or were already weak, fail after a few hours of use. Statistically, components that get beyond the initial few hours of use are likely to operate trouble free for several years before slowly beginning to become less reliable. Usually these later stages of unreliability are beyond the practical life of the product and thus not a concern. As such it can actually be better to repair a product that fails after the first few hours of use rather than replace it. That way there is assurance that the rest of the unit is good, having made it past the infant failure window, as opposed to rolling the dice again with a new unit.
Infrasonic: Refers to sounds or signals whose frequencies are below the normal human hearing range, generally considered to be 20 Hertz (see WFTD archive Hertz). The lowest audible frequency is not easy to absolutely define as it depends strongly on level. Some experiments have found that hearing can extend down to 10 Hz at very high levels. Sometimes the term "subsonic" is wrongly used to mean infrasonic. Subsonic actually refers to the speed of sound propagation through a medium and has noting to do with frequency or pitch.
Interleaving: A point in the signal path of a circuit where it is possible to interrupt the signal and "insert" another signal. Most commonly deployed in mixing boards it usually shows up as a patch point on each channel and/or bus output. The purpose is to be able to interrupt a signal in the mixer, bring it outside the mixer for some sort of special processing, and then return the processed signal to the same point from which it left. Common applications include applying compression, gating, or EQ to a particular channel without affecting any other channels or using any extra buses. Sometimes an insert is called a "patch" or "injection point."
Interleaving: A method of reducing errors in digital data, interleaving distributes and intermingles the consecutive bits or words of data, spreading them over a wider area on the storage media, and scattering potential errors. This helps protect against consecutive errors when the data is read back. A variety of different schemes for interleaving are used for CD, DAT and other medias, but as an example, on DAT one method uses one record head to write the right channel's even samples and the left's odd samples, while the other head writes the left channel's even samples, and the right's odd samples. In the case of a burst error (such as those caused by a dirty head), only half of either channel's samples will be affected, allowing interpolation to conceal the lost data. (See also WFTD "Linear Interpolation")
Intermodulation Distortion (IMD): The interaction of two or more frequencies in a signal that results in the generation of new frequency components not present in the original signal. These new components have frequencies equal to the sum and difference of the frequencies of the original signals, and integral multiples thereof. IMD is often a major issue in loudspeaker design due to the varying permutations of issues that arise as a speaker cone moves back and forth.
Intonation: Literally this means pitch, or using pitch. One who speaks with intonation uses pitch variations (presumably to help convey meaning). In our discourse of dealing with music, however, it has taken on a connotative meaning of describing pitch. When we refer to intonation we are often speaking of pitch accuracy or of relating to a pitch being produced. This is just how the word is often used in context. Similarly, intonation can also mean tuning, as in how an instrument is tuned. For example, sometimes a guitarist will say his guitar's "intonation is out." In this context he means that his instrument will not play in tune with itself.
Inverse Square Law: Useful when setting up a microphone or speaker, the inverse square law states that, in a free field the intensity of sound drops by 6 dB for each doubling of distance from the source. Now, none of us ever work in a truly free field (no reflective surfaces), but for most applications these numbers are accepted as workable. In real world terms, this means that for each time you double the distance between your sound source and a listener or microphone, the power of the audio drops by 75% - a fairly significant amount! How much is this in terms of volume? Well, it depends on the source you consult, we've seen both 6 dB and 10 dB convincingly listed as doubling or halving the volume (let's just say it's subjective and leave it at that...) - regardless, 6 dB is a very noticeable drop in level! Consider this the next time you place a microphone or speaker: Rather than just cranking up or attenuating the mic preamp or amplifier level for gain control, look at the distance to your source...
IPS: An abbreviation for Inches Per Second. IPS is normally used to describe tape speed in tape recording machines. A typical cassette recorder operates at 1 7/8 IPS, where reel to reel machines can range from 1/ 7/8 all the way up to 30 IPS. Faster speeds will sound better (all other things being equal) and have less noise, but can get expensive. A standard reel of 2-inch tape costs well over $100, and at 30 IPS will only hold about 15 minutes of music.
ISO: Abbreviation for The International Organization for Standardization. ISO is a worldwide federation of national standards bodies from some 130 countries, one from each country. A non-governmental organization established in 1947, the mission of ISO is to promote the development of standardization and related activities in the world with a view to facilitating the international exchange of goods and services, and to developing cooperation in the spheres of intellectual, scientific, technological and economic activity. ISO's work results in international agreements, which are published as International Standards. ISO is very active in producing manufacturing standards. These standards show up in the music industry more places than you would think. One of the more obvious places we run into ISO is in the organization of data for production of CD ROMs, which are often to ISO standards and are thus about as nearly universally readable as possible given all of the different platforms available. You can learn more about ISO at their Web site.
Isochronous: Signals which are dependent on some uniform timing or carry their own timing information embedded as part of the signal. Voice and video are isochronous signals, but data transfer is generally not.
ISRC: Abbreviation for the International Standard Recording Code. An ISRC is encoded into every manufactured compact disc. It contains information about the country of origin, the owner, the year of recording and the serial number of a recording. Some CD authoring programs allow the user to program the ISRC before burning discs.