Audio Terminologies That You Should Know II
1. Midi Termonologies
2. Operating systems terminologies
3. Signal processing terminologies
Active Sensing — A system used to verify that a MIDI connection is working. It involves the sending device sending frequent short messages to the receiving device to reassure it that all is well. If these active sensing messages stop for any reason, the receiving device will recognise a fault condition and switch off all notes. Not all MIDI devices support active sensing.
Aftertouch — A means of generating a control signal in a synthesizer based on how much pressure is applied to the keys of a MIDI keyboard. Most instruments that support this do not have independent pressure sensing for all keys, but rather detect the overall pressure by means of a sensing strip running beneath the keys. Aftertouch may be used to control such functions as vibrato depth, filter brightness, loudness and so on.
Bank — A specific configuration of sounds or other parameters stored in memory and accessed manually or via MIDI commands.
Breath Controller — A device that converts breath pressure into MIDI controller data.
Chase — A term describing the process whereby a slave device attempts to synchronise itself with a master device. In the context of a MIDI sequence, Chase may also involve chasing events — looking back to earlier positions in the song to see if there are any program change or other events that need to be acted upon.
Continuous Controller — Type of MIDI message used to translate continuous parameter changes, such as from a pedal, wheel or breath control device.
Dump — To transfer digital data from one device to another. A SysEx dump is a means of transmitting information about a particular instrument or module over MIDI, and may be used to store sound patches, parameter settings and so on.
Event — In MIDI terms, an event is a single unit of MIDI data, such as a note being turned on or off, a piece of controller information, a program change, and so on.
General MIDI — A universally agreed subset of the MIDI standard, created to enable manufacturers to build synthesizers, synth modules and plug-in instruments that exhibit an agreed minimum degree of compatibility.
GM Reset — A universal SysEx command which activates the General MIDI mode on a GM instrument. The same command also sets all controllers to their default values and switches off any notes still playing by means of an All Notes Off message.
GS — Roland’s own extension to the General MIDI protocol.
LSB — Least Significant Byte. If a piece of data has to be conveyed as two bytes, one byte represents high value numbers and the other low value numbers, much in the same way as tens and units function in the decimal system. The high value, or most significant part of the message is called the Most Significant Byte or MSB.
Local On/Off — A function to allow the keyboard and sound generating section of a keyboard synthesizer to be used independently of each other.
MIDI (Musical Instrument Device Interface): MIDI is a standard language of control messages that provides for communication between any MIDI-compliant devices. Anything from synthesizers to lights to factory equipment can be controlled via MIDI.
MIDI Channels: MIDI allows for 16 discrete channels for sending data.
MIDI Clock: A MIDI device-specific timing reference. It is not absolute time like MIDI Time Code (MTC); instead, it is a tempo-dependent number of “ticks” per quarter note. MIDI clock is convenient for synchronizing devices that need to perform tempo changes mid-song.
MIDI Controllers: MIDI controllers are a specific type of MIDI message.
MIDI Notes: MIDI notes are a specific type of MIDI message. Any MIDI sequencer or controller will send MIDI notes.
MIDI Port: A MIDI port is the physical MIDI connection on a piece of MIDI hardware. This port can be a MIDI in, out or through. Your computer must have a MIDI-capable card to output MIDI time code to an external device or to receive MIDI time code from an external device.
MIDI Time Code (MTC): MTC is an addendum to the MIDI 1.0 specification and provides a way to specify absolute time for synchronizing MIDI-capable applications. MTC is essentially a MIDI representation of SMPTE time code.
Sample Dump: A sample dump is the process of transferring sample data between music equipment. Because of the large amounts of data required to store digital sound, sample dumps may take a very long time when using the MIDI Sample Dump Standard (SDS). However, when using the faster SCSI MIDI Device Interface (SMDI) protocol, sample dumps can be performed many times faster.
Sample Dump Standard (SDS): The MIDI Sample Dump Standard is a way to transfer samples between music equipment. Samples transferred with SDS are sent across MIDI cables at the MIDI data rate of 31,250 Hz baud. SMDI is a much faster sample transfer method for musicians.
Virtual MIDI Router (VMR): A software-only router for MIDI data between programs. No MIDI hardware or cables are required for a VMR, so routing can only be performed between programs running on the same PC.
Operating systems terminologies:
ActiveX: A Microsoft technology that enables different programs to share information. ActiveX extends Microsoft Windows-based architecture to include Internet and corporate intranet features and capabilities. Developers use it to build user interactivity into programs and World Wide Web pages.
Adaptive Delta Pulse Code Modulation (ADPCM): A method of compressing audio data. Although the theory for compression using ADPCM is standard, there are many different algorithms employed. For example, Microsoft’s ADPCM algorithm is not compatible with the International Multimedia Association’s (IMA) approved ADPCM.
Algorithm — A sequence of instructions describing how to perform a specific task. Algorithms are often implemented in a computer language and compiled into a computer program. In the context of effects units, algorithms usually describe a software building block designed to create a specific effect or combination of effects.
Application (App) — Alternative term for computer program.
Audio Compression Manager (ACM): The Audio Compression Manager, from Microsoft, is a standard interface for audio compression and signal processing for Windows. The ACM can be used by Windows programs to compress and decompress .wav files.
Beta Version — Software which is not fully tested and may include bugs.
Binary — A counting system based on only two states: 1s and 0s. It is ideal for electronic equipment where it can be represented as high and low voltages, light on/off, N-S or S-N magnetic domains, etc.
BIOS — Part of a computer operating system (basic input-output system) held on ROM rather than on disk. This handles basic routines such as accessing the disk drive.
Bit — A contraction of Binary digit, which may either be 1 or 0.
Buffer Memory — A buffer is essentially a short term data storage facility used to accommodate variable data read or write periods, temporarily storing data in sequence until it can be processed or transferred by or to some other part of the system.
Bug — Slang term for a software fault or equipment design problem.
Byte — A collection of digital data comprising eight bits.
Codec: Coder/Decoder: refers to any technology for compressing and decompressing data. The term codec can refer to software, hardware, or a combination of both technologies.
Compression Ratio (file size): The ratio of the size of the original uncompressed file to the compressed contents. For example, a 3:1 compression ratio means that the compressed file is one-third the size of the original.
Computer — A device which can be instructed (or programmed) to carry out arithmetic or logical operations. Although mechanical ‘analogue’ computers do exist, most are now electronic and digital, and process digital data.
Copy Protection — A method used by software manufacturers to prevent unauthorised copying.
CPU — Central Processing Unit — the number-crunching heart of a computer or other data processor.
Crash — Slang term relating to malfunction of computer program.
Data — Information stored and used by a computer.
Defragment — The process of rearranging the files on a hard disk so that all the files are as contiguous as possible, and that the remaining free space is also contiguous.
Device Driver: A program that enables Windows to connect different hardware and software. For example, a sound card device driver is used by Windows software to control sound card recording and playback.
Digital Rights Management (DRM): A system for delivering songs, videos, and other media over the Internet in a file format that protects copyrighted material. Current proposals include some form of certificates that validate copyright ownership and restrict unauthorized redistribution.
DirectX: A set of Application Program Interfaces designed by Microsoft for multimedia development. A DirectX plug-in, such as the Noise Reduction DirectX Plug-In, uses the DirectX Media Streaming Services (DMSS) API. Because DMSS is a standard API, a DirectX plug-in can be used in any application that supports DMSS.
DMA — Direct Memory Access. Part of a computer operating system that allows peripheral devices to communicate directly with the computer memory without going via the central processor or CPU.
DOS — Disk Operating System. Part of the operating system of PC and PC compatible computers
Driver — A piece of software that handles communications between the main program and a hardware peripheral, such as a soundcard, printer or scanner. Also a term used to refer to a physical loudspeaker drive unit — eg bass driver.
Endian (Little and Big): Little and Big Endian describe the ordering of multi-byte data that is used by a computers microprocessor. Little Endian specifies that data is stored in a low-to-high byte format; this ordering is used by the Intel microprocessors. Big Endian specifies that data is stored in a high-to-low byte format; this ordering is used by the Motorola microprocessors.
Format — A procedure required to ready a computer disk or digital tape for use. Formatting organises the medium into a series of ‘electronic pigeon holes’ into which data can be stored. Different computers often use different formatting systems.
Fragmentation (cf. defragment) — The process by which the available space on a disk drive gets split up into small, sometimes unusable, sections due to the storing and erasing of files.
GUI — Graphical User Interface (pronounced ‘Gooey’). A software program designer’s way of creating an intuitive visual operating environment controlled by a mouse-driven pointer or similar.
IRQ — Interrupt Request. Part of the operating system of a computer that allows a connected device to request attention from the processor in order to transfer data to it or from it.
Media Control Interface (MCI): A standard way for Windows programs to communicate with multimedia devices such as sound cards and CD players. If a device has an MCI device driver, it can easily be controlled by most multimedia Windows software.
Microsoft Sound Mapper: The Sound Mapper is a special device that attempts to select the most appropriate sound card (map) on which to play a sound, or it will translate the sound into a format that can be played on your sound card.
Object Linking and Embedding (OLE): OLE is a technology developed by Microsoft to allow independent applications to behave as though they are tightly integrated. This allows objects such as audio files to be integrated into other applications such as a Microsoft Word document.
Real-Time Streaming Protocol (RTSP): A proposed standard for controlling broadcast of streaming media. RTSP was submitted by a body of companies including RealNetworks and Netscape.
Redirector File: A metafile that provides information to a media player about streaming media files. To start a streaming media presentation, a Web page will include a link to a redirector file. Linking to a redirector file allows a file to stream; if you link to the media file, it will be downloaded before playback begins. Windows Media redirector files use the .asx or .wax extension.
Windows Media Format: Microsoft’s Windows Media file format that can handle audio and video presentations and other data such as scripts, URL flips, images and HTML tags.
Signal processing terminologies:
Attack: The attack of a sound is the initial portion of the sound. Percussive sounds (drums, piano, guitar plucks) are said to have a fast attack. This means that the sound reaches its maximum amplitude in a very short time. Sounds that slowly swell up in volume (soft strings and wind sounds) are said to have a slow attack.
Attenuation: A decrease in the level of a signal.
Aliasing — When an analogue signal is sampled for conversion into a digital data stream, the sampling frequency must be at least twice that of the highest frequency component of the input signal. If this rule is disobeyed the sampling process becomes ambiguous as there are insufficient points to define each cycle of the waveform, resulting in unwanted enharmonic frequencies being added to the audible signal.
Anti-alias Filter — A very steep low-pass filter used to limit the frequency range of an analogue signal prior to A/D conversion so that the maximum frequency does not exceed half the sampling rate.
Band-pass Filter (BPF) — A filter that removes or attenuates frequencies above and below the centre frequency at which it is set, and only passes a specific range of frequencies. Band-pass filters are often used in synthesizers as tone shaping elements.
Bandwidth: When discussing audio equalization, each frequency band has a width associated with it that determines the range of frequencies that are affected by the EQ. An EQ band with a wide bandwidth will affect a wider range of frequencies than one with a narrow bandwidth.When discussing network connections, bandwidth refers to the rate of signals transmitted or the amount of data that can be transmitted in a fixed amount of time (stated in bits/second): a 56 Kbps network connection is capable of receiving 56,000 bits of data per second.
Boost/Cut Control — A single gain control which allows the range of frequencies passing through a filter to be either amplified or attenuated. The centre position is usually the ‘flat’ or ‘no effect’ position.
Chorus: Chorusing is an effect created by combining a signal with a modulating, delayed copy of itself. This effect creates the illusion of multiple sources creating the same sound.
Colouration — A distortion of the natural timbre or frequency response of sound, usually but not always unwanted.
Comb-Filter — a series of deep filter notches created when a signal is combined with a delayed version of itself. The delay time (typically less than 10ms) determines the lowest frequency at which the filter notches start.
Compressor — A device (analogue or digital) which is designed to reduce the overall dynamic range of an audio signal either by attenuating the signal if it exceeds a set threshold level according, or by increasing the level of quiet signals below a threshold. The amount of attenuation is defined by a set ratio, while the speed of response (attack) and recovery (release) can usually also be controlled.
Compression Ratio (audio): A compression ratio controls the ratio of input to output levels above a specific threshold. This ratio determines how much a signal has to rise above the threshold for every 1 dB of increase in the output. For example, with a ratio of 3:1, the input level must increase by three decibels to produce a one-decibel output-level increase:
Threshold = -10 dB
Compression Ratio = 3:1
Input = -7 dB
Output = -9 dB
Because the input is 3 dB louder than the threshold and the compression ratio is 3:1, the resulting signal is 1 dB louder than the threshold.
Crossover — A set of audio filters designed to restrict and control the range of input signal frequencies which are passed to each loudspeaker drive unit. A typical two-way speaker will employ three filters: a high-pass filter allowing only the higher frequencies to feed the tweeter, a low pass filter that allows only the lower frequencies to feed the woofer, and a second high-pass filter that prevents subsonic signals from damaging the woofer.
Crossover frequency — The frequency at which one driver ceases to produce most of the sound and a second driver takes over. In the case of a two-way speaker the crossover frequency is usually between 1 and 3kHz.
Cutoff frequency: The cutoff frequency of a filter is the frequency at which the filter changes its response. For example, in a low-pass filter, frequencies greater than the cutoff frequency are attenuated, while frequencies less than the cutoff frequency are not affected.
De-esser — A device for reducing the effect of sibilance in vocal signals.
Delay — The time between a sound or control signal being generated and it auditioned or taking effect, measured in seconds. Often referred to as latency in the context of computer audio interfaces.
Digital Delay — A digital processor that generates delay and echo effects.
Digital Reverberator — A digital processor which simulates acoustic reverberation.
Digital Signal Processing (DSP): A general term describing anything that alters digital data. Signal processors have existed for a very long time (tone controls, distortion boxes, wah-wah pedals) in the analog (electrical) domain. Digital Signal Processors alter the data after it has been digitized by using a combination of programming and mathematical techniques. DSP techniques are used to perform many effects such as equalization and reverb simulation.
Since most DSP is performed with simple arithmetic operations (additions and multiplications), both your computer’s processor and specialized DSP chips can be used to perform any DSP operation. The difference is that DSP chips are optimized specifically for mathematical functions while your computer’s microprocessor is not. This results in a difference in processing speed.
Direct Coupling — A means of connecting two electrical circuits so that both AC and DC signals may be passed between them.
Dither — A system whereby low-level noise equivalent to one quantising level is combined with a digitised audio signal in such a way as to perfectly linearise the digital system. Dither must be employed whenever the wordlength is reduced, otherwise quantising distortion errors will manifest.
Double-ended Noise Reduction — A method for removing or attenuating the noise component of a recording or transmission system, in which the signal is pre-conditioned in a specific way which is reversed on playback. Most analogue noise-reduction systems are of the double-ended type, such as the Dolby and DBX systems.
Dry (cf. Wet) — A signal that has had no effects added.
Ducking — A system for controlling the level of one audio signal with another. For example, in a broadcast radio context a music track can be made to ‘duck’ or reduce in volume whenever there’s a voice over.
Effects Loop — An interface system, usually involving separate send and receive connections, which allows an external signal processor to be connected into the audio chain. (cf. Insert Point)
Effects Return — An additional dedicated mixer input channel, usually with minimal facilities, designed to accommodate the output from an effects unit. (cf. Aux Return)
Encode/Decode — A system that modifies a signal prior to recording or transmission, and subsequently restores the signal on playback or reception.
Enhancer (cf. Exciter) — An audio processor designed to brighten audio material using techniques such as dynamic equalisation, phase shifting and harmonic generation.
Equalization (EQ): Equalizing a sound file is a process by which certain frequency bands are raised or lowered in level.
Exciter (cf. Enhancer) — An audio processor that works by synthesizing new high frequency harmonics.
Expander — A device designed to increase the dynamic range, typically by reducing the volume of low level signals (below a set threshold), or to increase the volume of high level signals (above a threshold).
FET-Compressor — A form of audio compressor in which an FET is used to provide variable signal attenuation. FET compressors are fast-acting in comparison to opto-compressors.
Filter (cf. Equaliser) — An electronic circuit designed to attenuate a specific range of frequencies. (See low-pass, high-pass and band-pass.)
Filter Frequency — The ‘turnover’ or ‘corner’ frequency of a high- or low-pass filter. Technically, the frequency at which the signal amplitude has been attenuated by 3dB.
Flanging — An effect which combines a modulated delay with the original signal, using feedback to create a dramatic, sweeping sound.
Gate — An electronic device (analogue or digital) designed to mute low level signals so as to improve noise performance during pauses in the wanted material.
Graphic Equalizer — An form of equalizer whereby multiple narrow segments of the audio spectrum are controlled by individual cut/boost faders. The name comes about because the fader positions provide a graphic representation of the EQ curve.
Harmonic Distortion — The addition of harmonics that were not present in the original signal caused by non-linearities in an electronic circuit or audio transducer.
High-Pass Filter: A high-pass filter attenuates all frequencies below a cutoff frequency. It is usually used to remove low-frequency rumble from audio files.
High-range (highs) — The upper portion of the audible frequency spectrum, typically denoting frequencies above about 1kHz.
Instrument Level — The nominal signal level generated by an electric instrument like a guitar, bass guitar or keyboard. Typically around -25dBu. Instrument signals must be amplified to raise them to line-level.
Limiting: Limiting is essentially a hard compressor. Limiting is often used to keep signals from going above a certain level, but can also be applied to create heavily compressed effects. Limiting should only be performed on peaks; if the Threshold level is set too low, heavy distortion will occur.
Limiter — An automatic gain-control device used to restrict the dynamic range of an audio signal. A Limiter is a form of compressor optimized to control brief, high level transients with a ratio greater than 10:1.
Linear — A device where the output is a direct multiple of the input with no unwanted distortions.
Line-level — A nominal signal level which is around -10dBV for semi-pro equipment and +4dBu for professional equipment.
Low-Pass Filter: A low-pass filter attenuates all frequencies above a cutoff frequency. Low-pass filters can be used as anti-alias filters or for general tonal shaping.
Noise-shaping: Noise-shaping is a technique which can minimize the audibility of quantization noise by shifting its frequency spectrum. For example, in 44,100 Hz audio quantization noise is shifted towards the Nyquist Frequency of 22,050 Hz.
Pan: To place a mono or stereo sound source perceptually between two or more speakers.
Quantization: Quantization is the process by which measurements are rounded to discrete values. Specifically with respect to audio, quantization is a function of the analog-to-digital conversion process. The continuous variation of the voltages of a analog audio signal are quantized to discrete amplitude values represented by digital, binary numbers. The number of bits available to describe these values determines the resolution or accuracy of quantization. For example, if you have 8-bit analog-to-digital converters, the varying analog voltage must be quantized to 1 of 256 discrete values; a 16-bit converter has 65,536 values.
Quantization Noise: Quantization noise is a result of describing an analog signal in discrete digital terms. This noise is most easily heard in low-resolution digital sounds that have low bit depths and sounds like a shhhhh-type sound while the audio is playing. It becomes more apparent when the signal is at low levels, such as during a fade out.
Resample: The act of recalculating samples in a sound file at a different rate than the file was originally recorded. If a sample is resampled at a lower rate, sample points are removed from the sound file, decreasing its size, but also decreasing its available frequency range. Resampling to a higher sample rate. This increases the size of the sound file, but does not increase the quality. When downsampling, be aware of aliasing.
Threshold: A threshold determines the level at which the signal processor begins acting on the signal. During normalization, levels above this threshold are attenuated.