Audio power amplifiers are classified primarily by the design of the output stage. Classification is based on the amount of time the output devices operate during each cycle of signal swing. Also defined in terms of output bias current, (the amount of current flowing in the output devices with no signal).

• Class A operation is where both devices conduct continuously for the entire cycle of signal swing, or the bias current flows in the output devices at all times. The key ingredient of class A operation is that both devices are always on. There is no condition where one or the other is turned off. Because of this, class A amplifiers are single-ended designs with only one type polarity output devices. Class A is the most inefficient of all power amplifier designs, averaging only around 20%. Because of this, class A amplifiers are large, heavy and run very hot. All this is due to the amplifier constantly operating at full power. The positive effect of all this is that class A designs are inherently the most linear, with the least amount of distortion.
• Class B operation is the opposite of class A. Both output devices are never allowed to be on at the same time, or the bias is set so that current flow in a specific output device is zero when not stimulated with an input signal, i.e., the current in a specific output flows for one half cycle. Thus each output device is on for exactly one half of a complete sinusoidal signal cycle. Due to this operation, class B designs show high efficiency but poor linearity around the crossover region. This is due to the time it takes to turn one device off and the other device on, which translates into extreme crossover distortion. Thus restricting class B designs to power consumption critical applications, e.g., battery operated equipment, such as 2-way radio and other communications audio.
• Class AB operation allows both devices to be on at the same time (like in class A), but just barely. The output bias is set so that current flows in a specific output device appreciably more than a half cycle but less than the entire cycle. That is, only a small amount of current is allowed to flow through both devices, unlike the complete load current of class A designs, but enough to keep each device operating so they respond instantly to input voltage demands. Thus the inherent non-linearity of class B designs is eliminated, without the gross inefficiencies of the class A design. It is this combination of good efficiency (around 50%) with excellent linearity that makes class AB the most popular audio amplifier design.
• Class AB plus B design involves two pairs of output devices: one pair operates class AB while the other (slave) pair operates class B.
• Class D operation is switching, hence the term switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each cycle. Since the output devices are either completely on or completely off they do not theoretically dissipate any power. Consequently class D operation is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching times -- a product we're still waiting for; meanwhile designs do exist with true efficiencies approaching 90%.
• Class G operation involves changing the power supply voltage from a lower level to a higher level when larger output swings are required. There have been several ways to do this. The simplest involves a single class AB output stage that is connected to two power supply rails by a diode, or a transistor switch. The design is such that for most musical program material, the output stage is connected to the lower supply voltage, and automatically switches to the higher rails for large signal peaks. Another approach uses two class AB output stages, each connected to a different power supply voltage, with the magnitude of the input signal determining the signal path. Using two power supplies improves efficiency enough to allow significantly more power for a given size and weight. Class G is becoming common for pro audio designs.
• Class H operation takes the class G design one step further and actually modulates the higher power supply voltage by the input signal. This allows the power supply to track the audio input and provide just enough voltage for optimum operation of the output devices. The efficiency of class H is comparable to class G designs.

A method of sound synthesis that relies on predefined waveforms to create sounds that vary over time. The amplitude, frequency and harmonic content of these waveforms can be manipulated to produce a vast number of different results.

To play the notes of a chord in succession rather than simultaneously.

A device that plays a pre-programmed series of notes. An arpeggio can be any kind of musical phrase, including simulations of guitar strumming.

A parameter that sets the speed at which an envelope or dynamics processor starts. With an envelope, Attack sets the speed at which the enveloped setting travels from 0 to its nominal value. In a dynamics processor, it sets the speed at which the processor starts working.

To reduce in volume.

A general word for sound.

A person interested in sound reproduction.

The memorization and playback of changes you make to mixer settings.

Auto Punch

A feature on V-Studios that automatically starts and stops recording for you when you're punching at locations you've set beforehand.

Short for "Auxiliary"; a designation for extra busses typically used for sending signal to effects, headphone amps and other destinations.

Aux Return

An extra input; typically used for receiving a signal from the output of an internal or external effect processor.

To make a copy of data and to store the copy on an external medium -- such as a CD-R or CD-RW disk -- for safekeeping. This copy is called a "backup." Backing up is extremely important to safeguard against unexpected events. To play or work on a song or project that's been backed up, it must be "recovered."

Referring to wiring: Audio signals require two wires. In an unbalanced line the shield is one of those wires. In a balanced line, there are two wires plus the shield. For the system to be balanced requires balanced electronics and usually employs XLR connectors. Balanced lines are less apt to pick up external noise. This is usually not a factor in home audio, but is a factor in professional audio requiring hundreds or even thousands of feet of cabling. Many higher quality home audio cables terminated with RCA jacks are balanced designs using two conductors and a shield instead of one conductor plus shield.

In EQ, a range of frequencies.

The total frequency range of any system. Usually specified as something like: 20-20,000Hz plus or minus 3 db. In EQ, the width of a band; the number of frequencies that are boosted or cut above and below a selected center frequency.

In MIDI instruments, a group of patches. Each bank can contains up to 128 patches, numbered from 0-127 or 1-128. In favorite lists, a group of patches.

Bank Select

A type of MIDI message that typically corresponds to a specific bank of patches. When an instrument receives a Bank Select message, the corresponding patch bank is selected. Typically, a Bank Select message is followed by a Program Change message that selects a patch within the selected bank. A Bank Select message may contain two components, an MSB ("Most Significant Byte") and/or an LSB ("Least Significant Byte") value.

The lower frequency range of a sound, usually from about 200 Hz down.

Bend Range

The maximum pitch change that can be applied by moving a pitch bend control.

Binary Numbers

A numbering system based on 2 in which 0 and 1 are the only available digits.

Bits (Bytes)

A binary digit. Mode of information used by a computer to store numbers. One bit equals a \Qone' or a \Qzero'. Usually 8 bits equals one byte, however, MIDI uses a 10 bit-byte that includes a start bit, the 8 - bit data message, and a stop bit.

Bit Depth

Digital recording can capture audio using number strings of varying lengths -- a longer string allows more detail in the description of level changes in the signal. The size of a string is referred to as its "bit depth." Most often, digital devices record and play audio using bit depths of 16 or 24 bits. Audio CDs use 16 bits.

Boomy

Listening term. Refers to an excessive bass response that has a peak(s) in it.

Boost

To increase in level.

Bouncing is the copying of tracks onto other tracks. Typically, this is done to combine a greater number of tracks into a fewer tracks, though there are other reasons to bounce. Some people call bouncing "ping-ponging."

Listening term. Usually refers to too much upper frequency energy.

An audio buffer is an area of RAM used to temporarily store data. Usually found in audio recording software. Reducing the buffer size can help reduce the amount of latency while recording and monitoring audio. Increasing the buffer size can help reduce pops and clicks while recording.

Bulk Dump

The transmission of a chunk of SysEx data from one MIDI device to another. The sending device doesn't need to understand the data -- it merely needs to be able to receive, store and re-transmit it.

"Burn" is music industry slang for writing data onto a CD.

A pathway down which one or more signals can travel to a common destination.

Bus Powered

Power for a piece of equipment is obtained from the FireWire or USB connection, no AC adapter is necessary.

Middle C in most MIDI devices.

CC Number (Control Change Number)

A numbered MIDI message that's permanently assigned to a particular parameter. A MIDI Control Change number is followed by a value that sets the parameter in the MIDI device that receives it.

CD-RW Drive

A CD-RW drive -- short for "CD-ReWritable" -- is a device that can burn audio onto CD-R ("CD-Recordable") or CD-RW ("CD-ReWritable") discs. You can write unerasable, permanent data onto a CD-R one time. A CD-RW disk can be reused: You can erase a CD-RW and write new data onto the disk.

An abbreviation for "Composite Object Sound Modeling" technology that shapes audio by applying the sonic characteristics of popular or classic microphones, guitars, guitar amplifiers and studio reference speakers.

Cannon Connector

Another name for an XLR connector.

Central Processing Unit (CPU)

A silicon chip that performs calculations and acts as the brain of a computer.

Typically, 1/100th of a semitone. Used in fine-tuning a pitch.

1. One of 16 different data paths that are available to carry messages in MIDI. 2. the audio path on a mixer.

Channel Message

A type of MIDI message that carries specific channel information.

Channel Strip

A row of controls on a mixer allocated to the shaping of a single audio signal.

A doubling effect commonly found on a synthesizer or sampler that makes a single sound appear to sound like an entire ensemble. The initial signal is split and appears at a slightly altered pitch from the original, or at a slightly later point in time. This time and pitch level are often controllable by a low frequency oscillator (LFO).

Refers to a type of distortion that occurs when an amplifier is driven into an overload condition. Usually the “clipped” waveform contains an excess of high-frequency energy. The sound becomes hard and edgy. Hard clipping is the most frequent cause of “burned out” tweeters. Even a low-powered amplifier or receiver driven into clipping can damage tweeters which would otherwise last virtually forever.

A timing reference that provides the basis for synchronization of different elements in a single device, or between multiple devices.

Coarse Tune

The adjustment of pitch in semitone steps.

Listening term. Refers to how well integrated the sound of the system is.

Listening term. A visual analog. A "colored" sound characteristic adds something not in the original sound. The coloration may be euphonically pleasant, but it is not as accurate as the original signal.

In audio, compression means to reduce the dynamic range of a signal. Compression may be intentional or one of the effects of a system that is driven to overload.

Compression Ratio

The amount of gain reduction applied to a signal exceeding a compressor's threshold level setting.

A dynamics processor that reduces the level of any signal exceeding a specified threshold volume.

Continuous Controller

A type of MIDI message that is generated by the movement of a continuous control.

Various sliders, levers, knobs, or wheels typically found on a MIDI controller. Used to send continuous (as opposed to discrete) data to control some aspect of a sound.

Core Audio

This is an ultra-low latency, high quality MAC-compatible audio driver that is built directly in to the OSX operating system.

Cross-talk

Unwanted breakthrough of one channel into another. Also refers to the distortion that occurs when some signal from a music source that you are not listening to leaks into the circuit of the source that you are listening to.

Cue Bus

A bus -- sometimes a stereo pair of busses -- dedicated to the providing of signal to performers so they can hear what they're doing.

To reduce in level.

The frequency at which a filter starts to work.

In a sound wave, the repeating movement from the greatest amount of air pressure to the least; the pitch of sound waves is measures in cycles; each cycle equals one "Hertz."

For "Digital-to-Analog Converter," a device that converts digital data to analog audio, such as the audio leaving a digital mixer on its way to an analog device.

Abbreviation for "Digital Audio Tape"; used in reference to this type of tape as well as the recorders that use it.

For "digital signal processing," the means by which digital audio is mixed, filtered, equalized, or by which effects are added.

Damper Pedal

Pedal that, when pressed, causes sustaining notes to continue to play until the pedal is released.

Damping (Damping factor, etc.)

Refers to the ability of an audio component to "stop" after the signal ends. For example, if a drum is struck with a mallet, the sound will reach a peak level and then decay in a certain amount of time to no sound. An audio component that allows the decay to drag on too long has poor damping, and less definition than it should. An audio component that is over-damped does not allow the initial energy to reach the full peak and cuts the decay short. "Boomy" or "muddy" sound is often the result of under-damped systems. "Dry" or "lifeless" sound may be the result of an over-damped system.

D-Beam

A real-time controller found on many Roland instruments. You can manipulate or trigger sounds by moving your hand above the D-Beam.

One of the four basic stages of a traditional envelope, decay is the time it takes for the enveloped setting to reach its sustain level after the Attack envelope stage.

Decibel (dB)

A decibel (or dB ) is 1/10th of a bel, which is a relative measure of two sounds. Named after Alexander Graham Bell. We perceive differences in volume level in a logarithmic manner. Our ears become less sensitive to sound as its intensity increases. Decibels are a logarithmic scale of relative loudness. A difference of approx. 1 dB is the minimum perceptible change in volume, 3 dB is a moderate change in volume, and about 10 dB is an apparent doubling of volume:

    · 0 dB is the threshold of hearing, 130 dB is the threshold of pain.

    · Whisper: 15-25 dB

    · Quiet background: about 35 dB

    · Normal home or office background: 40-60 dB

    · Normal speaking voice: 65-70 dB

    · Orchestral climax: 105 dB

    · Live Rock music: 120 dB+

    · Jet aircraft: 140-180 dB

De-esser

A device that detects and reduces sibilance in vocal signals.

The "normal" or "startup" state of a hardware device or software application.

Defrag, Defragment

The process by which the empty space on a hard drive or in a device's RAM is made continuous -- instead of being broken into small, scattered pieces -- to help ensure smooth operation.

A common effect that mimics the time difference between the arrival of a direct sound and the first reflection to reach the listener's ears.

A notch that you can feel as you move a fader up or down; signifies the point at which no level boost or cut is applied by the fader.

Digi-Score

A visual interface that displays a music score from any MIDI file. This virtual score constantly displays the exact location in the music file in several notation sizes.

Digital Audio

Sound represented as binary computer data. Typically used as the means for storing sound information in a computer or sampler.

Digital Music File

Music that is digitally recorded as a computer file. Common types of digital music files are .mid files -- the smallest and only really interactive type, also called a "Standard MIDI Files" -- .wav files -- very large, medium-resolution files, and MP3 files -- a highly compressed, high resolution file suitable for recording and playback.

Digital Synthesis

The use of numbers to create sounds. Method most often used in today's synthesizers for generating sounds, as compared to analog method employed previously.

Digital-to-Analog

The conversion, using a DAC, of digital data to analog audio.

A switch that allows you to quickly reduce your monitoring volume.

DIN Plug

A five-pin connector used by MIDI equipment.

Direct Box

A mic-level box that converts a phone connector to an XLR connector.

Direct Current (DC)

Current that moves in only one direction.

The spreading of sound waves as they leave a source. The spreading of sound waves as they leave a source.

Fuzz or roughness added to a sound that alters the musical signal. There are many forms of distortion, some of which are more audible than others.

A process that deliberately adds a tiny amount of noise to a signal in order to mask unwanted sounds introduced when the signal's original bit depth is reduced. Dithering is recommended when transferring audio to a device that uses a lower bit depth.

The artificial simulation of a second unison performance by using a delay with a short delay time.

In order for audio or MIDI interfaces to communicate (transfer data) to and from a computer, the use of software drivers is required. For use with a Windows machine, many products can use a standard 16 bit windows driver- these are already a part of a full install of Windows XP. Other interfaces require one or more special drivers to be installed. EDIROL products have an ADVANCED option or switch, which allows for a choice between the standard Windows driver, or in the ADVANCED mode, the specialized drivers. Deciding which driver to use will depend on the application being used and the USB/FIREWIRE hardware being used.

Drum Machine

An electronic device, usually controllable via MIDI commands, that contains samples of acoustic drum sounds. Used to create percussion parts and patterns.

A signal to which an effect has not been added.

Dynamic Headroom

The ability of an audio device to respond to musical peaks. For example, an amplifier may only be capable of a sustained 100 watts, but may be able to achieve peaks of 200 watts for the fraction of a second required for an intense, quick sound.

Dynamic Range

The range between the loudest and the softest sounds that are in a piece of music, or that can be reproduced by a piece of audio equipment without distortion (a ratio expressed in decibels). In speech, the range rarely exceeds 40 dB; in music, it is greatest in orchestral works, where the range may be as much as 75 dB.

Volume changes that occur in audio.

The process of altering the levels of frequencies that comprise a signal. Also called "equalization."

A delay-based effect in which copies of a signal are heard trailing off to silence; similar to shouting from a mountaintop and hearing your voice repeat.

Effect Loop

The process of adding an effect to a signal by sending a copy of the signal to an effect and mixing the effect's output with the original signal.

Effect Processor

A built-in or external device that produces effects.

Effect Return

An input that receives signal from the output of an internal or external effect.

Any of a variety of audio processes that can be applied to a signal to modify it, including reverb, delay, flanging, phasing.

Changes in a sound over time, including alterations in a sound's amplitude, frequency and timbre.

A device or process in a synthesizer or other sound generator that creates a time varying signal used to control some aspect of the sound.

Equalizer

An electronic set of filters used to boost or attenuate certain frequencies.

Equal Temperament

Standard Western tuning that divides each octave into twelve mathematically equal parts.

Error Correction

A procedure found in digital audio systems that detects and correct inaccurate or missing bits in the data stream.

Pleasing. As a descriptive audio term, usually refers to a coloration or inaccuracy that nonetheless may be sonically pleasing.

Expander

A device that reduces the level of a signal when it falls below a specified threshold to exaggerate its dynamic range.

An optional circuit board that can be installed in a device to add additional sounds or effect processing.

A multi-use computer key whose function is defined by software.

Abbreviation for "effects."

A feature of most audio editing software that allows the user to apply a gradual amplitude increase or decrease over some segment of the sound.

Also known as a slider or attenuator, this control is used for the precise manipulation of levels. In some devices, can also be used for the setting of parameter values. Sometimes found as a feature of MIDI software programs.

The delaying of a delay so that multiple images of the original signal are heard; also, the loud squeal that's heard when a channel is receiving its own output.

An electrical circuit which permits certain frequencies to pass easily while inhibiting or preventing others. Typical filters include low pass, high pass, band pass, and band reject.

Filter Envelope

A device that changes the Time Variant Filter's settings over a period of time.

The last stage of CD-R/RW writing in which the disk's table of contents (TOC) is written onto the disk.

Fine Tune

The adjustment of pitch in the smallest of increments, typically 100ths of a semitone, or "cents."

FireWire Audio Interface

A FireWire interface allows the transfer of audio to and from a computer via a FireWire connection, the use of software drivers is required. EDIROL FireWire interfaces do not require the installation of driver software when being used with MAC OSX.

An effect that generates a swirling sound by adding a slightly delayed copy of the signal in which the copy's delay time fluctuates.

Flat Response

The faithful reproduction of an audio signal; specifically, the variations in output level of less than 1 dB above or below a median level over the audio spectrum.

Flex Bus

A powerful all-purpose bus available on Roland digital mixers.

On an in-line mixer, the act of allocating a channel's tools to the control of an input signal or to the control of a multitrack tape return.

When working with two signals 180 degrees out of phase, delaying one of the signals so that its phase lines up with the other.

Flying Fader

A motorized fader that automatically moves to its current setting.

FM Synthesis

A synthesis method that involves the interaction of a signal (carrier) by another (modulator).

Harmonic content of a sound that determine the sound's character, especially important in human vocal sounds, where formants are produced by mouth shape and vocal cord length.

The breaking up of a large space -- a hard drive or onboard RAM memory -- into smaller, disconnected chunks of space that prevent data from being stored in one continuous area. Fragmentation can cause operational problems.

In SMPTE and MTC time codes, seconds are divided into frames as determined by the current frame rate.

Refers to the number of times per second that a sound wave's cycle repeats, with a greater frequency resulting in a higher perceived pitch; also used as shorthand for describing sound waves in audio by their pitch. The range of human hearing is commonly given as 2-20,000Hz (20Hz-20kHz). One hertz (Hz) represents one cycle per second, 10Hz represents 20 cycles per second and so on. Lower numbers are lower frequencies.

Fundamental Frequency

The predominant frequency in a complex waveform. Typically provides the sound with its strongest pitch reference.

Abbreviation for "General MIDI" and "General MIDI 2," respectively.

GPI is short for "General Purpose Interface," a control jack found on some video editing devices.

Roland's extension of General MIDI. GS adds features such as chorus, reverb and panning for more realistic sound, and expands beyond the original 128 sounds of General MIDI to 16,000-plus sounds. This open-ended convention has been licensed by Apple for QuickTime 3.0, 4.0 & 5.0, by Microsoft for their GS synthesizer, and by Nintendo for their sound applications.

To increase in level. The function of a volume control.

A device that turns audio off or down when it falls below a specified threshold.

General MIDI

General MIDI -- or "GM" -- is a music industry standard ratified in 1991. It established a set of 128 synth, orchestral and percussion sounds so that GM files and Standard MIDI Files play back on any GM-compatible instrument with predictable results.

General MIDI 2

General MIDI 2 -- or "GM2" -- is an update to the General MIDI standard. It was ratified in 1991. GM2 was adopted by Roland and Yamaha to extend the set of GM sounds, expressive musical parameters and other features in order to provide for more consistent playback of GM2-compliant files on different instruments.

Listening term. A sonic analog of the grain seen in photos. A sort of “grittiness” added to the sound.

Graphic Equalizer

A device type that applies a series of bandpass filters to a sound, each of which works on a certain range of the spectrum. The frequencies that fall within the range, typically one-third octave, can be boosted or cut.

A common zero voltage reference in a system of connected audio devices; when devices have different zero voltage references, ground hum may occur.

A process by which multiple channels are joined together under a single level control.

Haas Effect

If sounds arrive from several sources, the ears and brain will identify only the nearest. In other words. If our ears receive similar sounds coming from various sources, the brain will latch onto the sound that arrives first. If the time difference is up to 50 milliseconds, the early arrival sound can dominate the later arriving sound, even if the later arrival is as much as 10 dB louder. The discovery of this effect is attributed to Halmut Haas in 1949.

Hard Drive

A device that uses magnetism to store data on a rigid platter mounted inside its case.

Also called overtones, these are vibrations at frequencies that are multiples of the fundamental. Harmonics extend without limit beyond the audible range. They are characterized as even-order and odd-order harmonics. A second-order harmonic is two times the frequency of the fundamental; a third-order is three times the fundamental, and so one. Each even-order harmonic—.second, fourth, sixth, etc.—is one octave or multiples of one octave higher than the fundamental; these even-order overtones are therefore musically related to the fundamental. Odd-order harmonics—third fifth, seventh, etc.—create a series of notes that are not related to any octave overtones and therefore may have an unpleasant sound. Audio systems that emphasize odd-order harmonics tend to have a harsh, hard quality.

Harmonic Series

Also known as the "overtone'' series, this is the series of frequencies in a sound that are whole number multiples of the fundamental.