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Analog Sequencer
In music creation, a type of sequencer that does not use digitized performance information like we are accustomed to in modern designs. Analog sequencers were common in the 1970's and early 1980's, until digital sequencers came along and with their vastly more comprehensive capabilities made analog sequencers obsolete. Most analog sequencers work by manually setting a series of note values in a sequence. This may be as simple as having a series of sliders (like a graphic equalizer) that each control a VCO (Voltage Controlled Oscillator). Each slider in a series is set so it causes the VCO to play a particular pitch or note. A clock source causes the "sequencer" to step through these sliders so each one is read individually one right after the other. The result is playing a sequence of notes based on the values of the sliders and the speed of the clock. Analog sequencers may have just a few steps available, or they may have many steps and some method to disable or mute some steps for rests and shorter sequences. Analog sequencing has made a bit of a comeback in recent years as part of the trend towards "retro" equipment. While not offering anywhere near the depth of versatility of a digital sequencer, they do have some advantages in that they are easy to program without having to perform the musical part and they are easy to interface with analog synthesizers.
British EQ
Today's Word for the Day was a special request from one of our inSync readers. British EQ - Can be loosely defined as any equalizer circuit that is designed and built in a way that emulates (in design or sound or both) the classic EQ circuits from the legendary mixers that came out of England in the 1950's, 60's and 70's. Soundcraft, Amek, Neve, Trident, and many other brands achieved legendary status during those years because engineers and producers liked their sound, and in particular liked the performance and sound of their equalizers. During the 1980's and 90's less expensive products began to show up from other parts of the world. British EQ was thus coined as a marketing term that became used by many of the English companies to combat the less expensive products. They felt that by making the distinction that not all mixers and EQ circuits sound the same they could maintain market share even at higher prices. By all accounts the idea worked because there is still today quite a bit of mystique around the concept of British EQ.
Center Frequency
As it pertains to equalizers the center frequency is the exact frequency to which the EQ filter is tuned. Equalizers are filters - at least analog ones are (most digital ones are programmed to emulate filter behavior). When you boost or cut an EQ frequency you are always changing the gain more than just that one frequency as determined by the Q of the filter circuit (or digital program). The center frequency is where the most change takes place (boost or cut), and the filter has progressively less effect on frequencies that are further and further away from the center frequency.
Compressor
A compressor is a device that reduces the dynamic range of an audio signal. First a threshold is established. When the audio signal is louder than this threshold, its gain is reduced. The amount of gain reduction applied depends on the compression ratio setting. For example, with a 2:1 ratio, for every 2 decibels the input signal increases, the output is allowed to increase only 1 decibel. A variety of other parameters in the compressor will also affect its performance processing specific signals; attack time, release time and others are very important.There are a variety of uses and applications for compressors, the most obvious one being to control the dynamic range of a live performance so that it will fit into the fairly narrow dynamic range of recorders, etc. Other applications include making a signal's average level higher, increasing the apparent sustain on a guitar, evening out a vocal or bass guitar performance, fattening up sounds, and on and on. The list of possibilities is extensive!
Cut-Only Equalizer
Term used to describe graphic equalizers designed only for attenuation (also referred to as notch equalizers, or band-reject equalizers). The flat (0 dB) position locates all sliders at the top of the front panel. The filters (normally spaced at 1/3-octave intervals) all start at 0 dB and reduce the signal on a band-by-band basis. Proponents of cut-only philosophy argue that boosting runs the risk of reducing system headroom. Historically many cut-only EQ's have been passive devices, which in some audiophile circles means they have the potential to sound better (no op amps = less distortion and noise).
Cutoff Frequency
In a filter, the cutoff frequency is the point where the response is 3 dB down in amplitude from the level of the passband. Beyond the cutoff frequency, the filter will attenuate all other frequencies, depending on the design of the filter. On a sweepable shelving EQ or filter, what you are "sweeping" (or changing) is the cutoff frequency. To our ears, this changes the point at which the filter is operating.
Equal Temperament
There are many different scaling or tuning systems that define how individual notes are tuned in relation to each other. Equal Temperament is a Scaling system where the octave (see WFTD archive octave) is divided into 12 equal parts. The ratio of the frequencies between any two adjacent notes is exactly the same. Most keyboard instruments are scaled in this manner.
Equalizer
Based on the root word, equal, an equalizer is an audio device whose function is to equal out the tonal characteristics of a sound. At least that was the idea back in the days when they were first conceived as a tool used to get flat response in telephone lines and to make up for the deficiencies in audio equipment and acoustic spaces. Nowadays it could more aptly be named an "unequalizer" since they are more often used creatively to alter the relative balance of frequencies to produce desired tonal characteristics in sounds. An equalizer has the ability to boost and/or cut the energy (amplitude) in specified frequency ranges by employing one or more filter circuits. There are many different types of EQ's in use today in many widely varying applications, but they fundamentally all do the same thing.
Equivalent Input Noise (EIN)
A rating of the overall noise performance of an amplifier (typically a microphone preamplifier). Basically, this is a measure of how much noise a mic preamp will add to a microphone's signal. Measurements are normally made with a 150 Ohm resistor on the preamp to simulate the load a mic would present. The theoretical limit on EIN is -130.0 to -131.8 dBm (the thermal noise generated by the resistor). When comparing this spec, keep in mind that larger negative values are better (i.e. -124 is better than -118). But don't place TOO much weight on this spec, most current EIN specs are infinitesimally small (can you REALLY hear the difference between -120 dBm and -122 dBm??)
Expander
The opposite of a compressor. Where a compressor takes a given dynamic change and reduces it, an expander increases it, making changes larger. Expanders are used to "un-do" compression in some circuits (companding). More commonly, expanders are used for noise reduction. In this application (downward expansion), a threshold is set at a level below desired audio signals, but above the noise floor. When signal drops below the threshold, expansion is applied, pushing signal even further down, reducing the level of noise. For example, an expander might be set up with a 1:6 ratio. This means that for every 1 dB of input level change the expander sees, it will output a 6 dB change. When a signal drops below the threshold by 2 dB, the output of the expander will drop by 12 dB, similarly dropping the level of any background noise floor. (See also "Compressor" and "Ratio" in the WFTD archives).
Feedback Eliminator
A product category that has become popular in the last 15 years. The Feedback Eliminator is a type of automatic, electronic equalizer. They work by finding the frequency of feedback and then tuning a precision, narrow bandwidth equalizer to it and cutting the level of that exact frequency until the feedback stops. A good feedback eliminator can go through this entire procedure in a few milliseconds, which means feedback can be stopped and controlled before it gets out of hand. It also means they can be used very effectively in live situations where feedback may occur at different frequencies over the course of a performance (for any of a dozen reasons). Like most product categories that have reached maturity, feedback eliminators come in many different configurations, brands, and price ranges. There are many different capabilities available within the general category, but for the most part the basic purpose is the same: to control feedback problems.
Frequency
Literally the number of times something occurs per unit of time. In the audio world the frequency of sound vibrations are directly related to what we hear as pitch, though the relationship is NOT linear. It is also inversely related to wavelength. We use the word frequency, and the values associated with it, as an objective way to speak about sound characteristics. Saying a unit has a frequency response of 20 Hz to 20kHz is much more accepted than specifying the response in terms of pitch.
Frequency Agile
A term used in the communications industry to signify equipment that can operate on more than one frequency. It sometimes implies that the frequency selection is done automatically by the device. In our industry this term is used to denote wireless systems where the frequency (or channel as it is often called) can be varied by the user. This is an important attribute for touring acts because they need to use different frequencies in different locations due to television stations and other possible interference in a particular area.
Frequency Doubling
Generally caused by overloading a low-frequency speaker, frequency doubling makes bass instruments sound an octave higher than they really are. This is because the overdriven speaker is making the second harmonic louder than the fundamental pitch.
Frequency Modulation (FM)
The changing of the frequency of a "carrier" in response to a "modulating" signal, usually an audio waveform. As the modulating signal voltage (amplitude) varies up and down the frequency of the carrier varies up and down from its nominal unmodulated value. In music, vibrato is a form of frequency modulation because it is a periodic variation in frequency (pitch). In FM broadcasting the audio signal is used to modulate a high frequency carrier that is then transmitted. At the receiving end a special circuit called a FM detector, or "discriminator" is used to recover the audio from the modulated signal. FM is considered a better (than AM - Amplitude Modulation) method of transmitting radio and TV signals because the FM signal is not as sensitive to amplitude variations caused by atmospheric interference. FM is also used as a sound synthesis technique (see FM Synthesis).
Frequency Response / Frequency Range
From inSync reader Kevin T. comes the following question (which qualifies as both a WFTD and a TTOTD): What is the difference between frequency response and frequency range as it pertains to studio reference monitors?Kevin, first of all, thanks for the question! According to the Unabridged inSync Master Dictionary (which we make up as we go...): Frequency Range is the actual span of frequencies that a monitor can reproduce, say from 5 Hz to 22 kHz.Frequency Response is the Frequency Range versus Amplitude. In other words, at 20 Hz, a certain input signal level may produce 100 dB of output. At 1 kHz, that same input level may produce 102 dB of output. At 10 kHz, 95 dB, and so on. A graph of all the frequencies plotted versus level is the Frequency Response Curve (FRC) of the monitor.When you see a Frequency Response specification for a monitor, the manufacturer is telling you that for a given input signal, the listed range of frequencies will produce output within a certain range of levels. For example: 20 Hz to 20 kHz ± 3 dB. For these frequencies, the monitor will output signals that are within a 6 dB (± 3 dB) range. This does not mean that the speaker won't reproduce frequencies outside this range, it will! But frequencies outside the range will be more than 3 dB off from the reference level. For further information, see also May 5th's inSync Word For The Day, "Flat Response", available in the inSync Archives.
Gate
A dynamics device whose function is to remove unwanted audio material below a certain threshold. Some type of "gain cell" is employed (usually a VCA) that can raise or lower the volume of the audio going through the unit. When the signal falls below a certain threshold that is set the gain cell will quickly drop the audio level down to a predetermined level. This level is usually very low, or even off, but in some applications it may only be a reduction of a few dB. The reason they are called gates is because when they "close" it sounds as if the audio has suddenly stopped, or has been "gated." Now, it is possible to set many gates for slower response time so the effect is not as sudden, but often a sudden change is what is desired. Gates are often used on drum tracks to prevent bleed from other nearby drum mics, and they are sometimes used on noisy sources so when the desired audio signal stops the noise is automatically muted. The gated reverb sounds made popular by Phil Collins and Peter Gabriel in the 1980's were the result of running a reverb's decay through a gate. When the reverb level fell below a certain threshold the sound would abruptly cut off.
Graphic Equalizer
A type of EQ that is configured to provide a graphic display of the EQ settings. Years ago equalizers were all rotary knob based. When units began to arrive on the scenes that had 15, 30, or even 45 bands (frequencies) they could EQ at once it became difficult to see what was going on at a glance. Looking at a row of 30 knobs to get an overall idea of the EQ curve is pretty difficult. So equalizers that used sliders instead of knobs were developed and quickly won the favor of engineers due to their improved ergonomics. People liked how easy it was to see the overall EQ curve at a glance, but they also just liked using sliders more than knobs (something that we'd already figured out about mixers). The ONLY thing that makes an EQ "graphic" is this configuration of being able to see the curve at a glance. Contrary to popular belief there are graphic EQ's that have the same features as parametric EQ's, including Q controls and sweepable frequencies. Most graphic EQ's, however, only give you control of cutting or boosting a pre-selected set of frequencies at a pre-selected Q.
Image frequency
In wireless systems using heterodyne tuning systems, an undesired carrier frequency that can produce the same intermediate frequency (IF) as the proper carrier frequency. While precautions are taken to filter these frequencies before they get in to the system they can still sometimes be mistakenly accepted and processed by the receiver, which will result in poor performance and interference (at least intermittently).
Interrupt/Interrupt Request (IRQ)
A temporary suspension of a process. In PC computers interrupts are used to suspend one activity in order to give priority to another more important activity. Interrupt signals, also known as Interrupt Requests (IRQ) are identifiable by a unique number and can have varying levels of priority, but in general they all cause the OS to stop what it is doing and decide what to do next. They can come from software or hardware devices. Many things you do on a regular basis, such as pressing a key on your keyboard or clicking your mouse generate an interrupt that causes the computer to take some action based on how it is programmed to handle that particular interrupt. MIDI and other music related hardware connected to PC computers generally need to have unique IRQ identities in order for communication between the computer and the hardware to take place properly. To that end there are methods for choosing the ID on most hardware that is to be connected to a PC. A similar analogy would be SCSI devices, where each one has to have a unique ID number. PC computers have routines known as Interrupt Handlers and Interrupt Schedulers that enable them to manage the regular flow of I/O for the system and keep everything running smoothly and on time.
Limiter
A limiter is a dynamics processor very similar to a compressor (see inSync WFTD 10/13). In fact, many compressors are capable of acting as limiters when set up properly. The primary difference is the ratio used in reducing gain. In a limiter, this ratio is set up to be as close to infinity:1 as possible (no matter how much the input signal changes, the output level should remain pretty much constant). The idea is that a limiter establishes a maximum gain setting, and prevents signals from getting any louder than that setting.Like compressors, limiters are used for a variety of applications. A few: Maximizing signal levels while preventing distortion when using digital recorders, preventing overload in a signal chain, setting a maximum volume level to protect users of in-ear monitors, protecting speakers and amplifiers from clipping, and so on. Any time you want to establish a maximum gain setting and prevent signals from passing it, a limiter is your tool of choice!
Low Frequency Oscillator (LFO)
An oscillator is an electronic circuit which produces periodic or regularly repeating waveforms; i.e. sine, square, sawtooth, or triangle waves. An LFO is an oscillator producing these waveforms at a very low frequency or pitch. These slowly vibrating, generally subsonic waves (0 - 20 Hz or so) are often used to modulate or change a parameter in a synth, sampler, or effects processor. One common application is modulating the pitch of an audio oscillator with an LFO; this results in vibrato. If the volume of an audio oscillator is modulated with an LFO, the result is tremolo. Just about any time you see a "modulation" control on a device, it is controlling an LFO, and being used to periodically change some parameter.
Multiband Compressor
A specific type of compressor that looks at specific frequency bands of audio and acts on them independently. For example, a multiband compressor can be set to only compress frequencies below 100 Hz, which would prevent a potential build up of low frequency content in a PA system or broadcast. Or it can be used as a mastering tool to aid in adjusting the overall spectral balance of a recording. Keep in mind this is fundamentally different than using a standard compressor with a sidechain. In that case the compressor is always acting on the whole signal, whereas a multiband compressor only acts on specific frequency ranges. One has to be careful, however, because misuse of a multiband compressor can result in skewed tonality. If you compress the high frequencies of a signal going to cassette tape (because you want to print more overall level to tape) to the point where the material ends up sounding dull you have defeated the purpose.
Nyquist Frequency
In audio it is the highest frequency that may be accurately sampled based upon the sampling rate. It is based on the Nyquist Theory, which applies to many different fields where data is captured. In general terms the Nyquist Theory is the minimum number of resolution elements required to properly describe or sample a signal. In order to reconstruct (interpolate) a signal from a sequence of samples, sufficient samples must be recorded to capture the peaks and trough of the original waveform. In digital audio the Nyquist Frequency is half of the sampling rate. For example, when a digital recording uses a sampling rate of 44.1kHz, the Nyquist frequency is 22.050kHz. If a signal being sampled contains frequency components that are above the Nyquist limit, aliasing will be introduced in the digital representation of the signal unless those frequencies are filtered out prior to digital encoding. For those who want the gory details there is an excellent paper called Consequences of Nyquist Theorem for Acoustic Signals Stored in Digital Format available at the Digital Recordings website.
Optical Compressor
A type of audio compressor that uses an electro optical attenuator to control the dynamics of the processed signal. An electro optical attenuator basically consists of a light source whose intensity is proportional to the level of the input signal, and a photoconductive cell whose resistance decreases as the light intensity presented to it increases. This photoconductive cell controls the volume of the amplifier that attenuates the volume of the output signal. Thus when a louder signal is input, the light shines brighter, the photocell's resistance goes down, and the amplifier reduces its gain, producing the effect of audio compression - for each dB that the input signal exceeds the threshold, the output rises by something less than a dB depending upon how the ratio is set and the exact properties of the photo cell circuit being used.
Paragraphic Equalizer
Basically this is an EQ that combines the user interface of a graphic equalizer with the functionality of a parametric equalizer. The EQ adjustments are made with sliders (so you get a visual graphic representation of your settings), but each band has adjustable frequency and Q like a parametric. Plus there are often other attributes that can be set. Very few hardware based paragraphic EQ's have been built over the years because they require a lot of components (thus are expensive) and space to lay them out in a usable fashion (especially if long throw faders are employed). However, in software based systems, the paragraphic EQ doesn't need to cost much more than any other type and are more popular, though they still can take up a lot of space on screen.
Parametric Equalizer
A type of equalizer having several "parameters" for control of various filters that can be applied to audio signals. Parametric equalizers are most widely used in situations where very fine control over the audio signal is desired. In order for an equalizer to be parametric it must at least have control over gain, Q, and frequency. In most cases each of these controls are on rotary potentiometers, but there are a few graphic style parametric equalizers on the market. Some equalizers have selectable frequencies that can be adjusted, but no Q control. These are known as quasi-parametric or sweepable equalizers.
Plate Reverb
A type of synthetic reverberation system. Plate reverbs were one of the first types of artificial reverbs used in recording. They used a steel plate under tension supplied by springs at the corners where the plate was attached to an outer shell. The plate gets vibrated in accordance with a signal from a transducer and the vibration is sensed elsewhere on the plate with a contact microphone of one type or another. Put your ear up to any large metal item and tap on it and you will hear how steel plates were used to create reverb. Plates were initially used a great deal in the early days of studio recording (even though they don't sound that much like natural reverberation) due to their relatively small size and low cost when compared to a reverberation room. While many other types of artificial reverbs appeared on the scene (spring, etc.) the plate reined king until the advent of digital reverbs. While in many cases early digital reverbs sounded even less like natural reverb than plates did, they did offer the function at a much lower price and in a much smaller package. Ultimately digital reverbs prevailed sonically as well, and even began to include plate simulations in their algorithms. Of course there are many engineers who still prefer the sound of a good old plate, just like they like other types of vintage equipment.
Resonant Frequency
The frequency at which resonance occurs. The resonant frequency determines the pitch of things like recorders and other musical instruments that rely on resonant columns of air. It also determines the pitch of feedback, another form of resonance. And it is the pitch or frequency the port of a loudspeaker may be tuned to.
Reverb
The remainder of sound that exists in a room after the source of the sound has stopped is called reverberation, sometimes mistakenly called echo (which is an entirely different sounding phenomenon). We've all heard it when doing something like clapping our hands (or bouncing a basketball) in a large enclosed space (like a gym). All rooms have some reverberation, even though we may not always notice it as such. The characteristics of the reverberation are a big part of the subjective quality of the sound of any room in which we are located.Our brains learn to derive a great deal of information about our surroundings from the sound of a room and it's reverberation. Consequently it is necessary to have the proper type and amount of reverberation on recordings in order for them to be aesthetically pleasing or to sound natural to us. This can be accomplished with careful microphone placement, but it is often necessary to employ artificially created reverb.To create reverb, a device known as a reverb unit is employed. Reverb units have historically come in many shapes and sizes, and have used many different techniques to create the reverberation. These days most of the reverb units employed throughout the world are digital, where the sound of the reverb is generated by a computer algorithm and mixed with the original signal. We will be discussing other types of reverb units in the future.
RIAA Equalization
Also referred to as RIAA curve or RIAA de-emphasis curve. These all refer to a standard initially proposed by the RIAA for vinyl phonograph record mastering and playback. Due to some of the physical limitations of phonograph records and the playback systems available back when they were developed, the curve was set up to allow the record pressing plant (and mastering facility) to "pre-emphasize" higher frequencies, which evened out the size of the grooves making high quality records much easier to manufacture. The curve acts as a sort of equalizer, attenuates low frequencies and amplifies high frequencies (relative to a 1 kHz reference point) in order to achieve the maximum dynamic range for a lateral cut vinyl disc. The grooves in a stereo phonograph disc are cut by a chisel shaped cutting stylus driven by two vibrating systems arranged at right angles to each other. The cutting stylus vibrates mechanically from side to side in accordance with the signal impressed on the cutter. The resultant movement of the groove back and forth about its center is known as groove modulation. The amplitude of this modulation cannot exceed a fixed amount or "cutover" occurs. Cutover, or overmodulation, describes the breaking through the wall of one groove into the wall of the previous groove. Since low frequencies cause wide undulations in the groove, they must be attenuated to prevent overmodulation. At the other end of the audio spectrum, high frequencies must be amplified to overcome the granular nature of the disc surface acting as a noise generator, thus improving signal-to-noise ratio.
Semi-Parametric EQ
Sometimes called pseudo or quasi-parametric EQ, a semi-paramteric EQ is a parametric equalizer that has one or more features missing. This term is sometimes used to describe a single band of equalization, where it generally means a parametric EQ that does not have a Q control (the Q is fixed). The term is also used to describe entire equalizer sections, which may contain several bands of EQ. In those cases it generally means one or more of the bands in question is not a full featured parametric; again it is usually the Q control that is missing. For example, a mixing board with a semi-parametric EQ may have a four-band equalizer on each channel, but only two of those four may be fully parametric (implying the other two do not have the Q control).
Sequencer
In music production, a sequencer is a hardware or software device designed to record performance data and play it back in sequence, or in a specific order of events. Early sequencers were analog and programmed by setting a series of voltages (representing pitch) with potentiometers that triggered VCO's. The playback involved having a clock step through or trigger each of these "events" in sequence. Modern sequencers have evolved well beyond that original concept and now have very sophisticated editing and performance features. Nowadays a large percentage of music composition and arrangement is done with sequencers and MIDI instruments. We also now have sequencers with digital audio recording and editing capabilities built in.
Soft Limiter
Soft limiting is basically applying a soft knee type of process to a limiter. Soft limiting rounds the peaks of audio to allow a hotter signal to be printed to tape or disk without clipping. It comes in especially handy for digital recording. Digital converters are more accurate at higher levels (up to clipping) so applying a soft limiter to the signal allows the overall signal to be captured several dB hotter while not sounding overly compressed (only the peaks are altered). In many ways a properly configured soft limiter will emulate the natural characteristics of analog tape saturation and can thus produce a very pleasing and familiar sound in digital recording.
Ultra High Frequency
Abbreviation for Ultra High Frequency. Similar to VHF, UHF pertains to a band or range of radio frequencies defined by the FCC (Federal Communications Commission) to be used for some television stations and a wide variety of wireless two-way communication systems. UHF picks up where VHF leaves off, having a frequency range of between 300 MHz and 3000 MHz.
Very High Frequency
Abbreviation for Very High Frequency. VHF pertains to a band or range of radio frequencies defined by the FCC (Federal Communications Commission) to be used for some television stations and a wide variety of wireless two-way communication systems. The frequency range of VHS is between 30 MHz and 300 MHz.
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