Alphabet Soup

This month we're going to wade through the morass of acronyms and abbreviations you need to know to make sense of articles and ads aimed at desktop musicians.

This month we're going to wade through the morass of acronyms and abbreviations you need to know to make sense of articles and ads aimed at desktop musicians. A truly comprehensive glossary would fill a book, so we've focused on common, yet commonly misunderstood, alphanumeric combinations from the audio, computer, and Internet vernaculars. To dig deeper, check out the excellent audio reference at Rane's Web site (, E-mu's Glossary of Electronic Music Terms (, or the PC Technology Guide (

Our goal is to help you attain a practical understanding of basic concepts and terminology, so if you're looking for obscure details to impress the Ph.D.s at your next MENSA soiree, you're out of luck. Pragmatic readers, read on.

AC-3 (also Dolby Digital). A perceptual-encoding format that compresses six channels of digital audio in the now common "5.1" surround setup. The "5" refers to five full-range channels-left, center, right, left rear, and right rear-and the ".1" refers to the LFE (low-frequency effects) channel. The 5.1 surround standard for DVD-Audio does not use AC-3. Instead, it uses Meridian Lossless Packing (MLP) to compress six full-range channels of 24-bit, 96 kHz audio without data loss.

ADC (also A/D converter). Analog-to-digital converter. A circuit that translates analog audio into digital format. In simple terms, an ADC measures (samples) the amplitude of a waveform 44,100 times per second and describes it as a 16-bit binary number for "CD quality" audio. First, however, it must filter out the frequencies above 22.1 kHz to avoid the distortion predicted by the Nyquist Theorem, which is beyond the scope of this month's column.

ADSL. Asymmetric digital subscriber line. A very high-speed Internet connection that's called "asymmetric" because it's capable of much faster download speeds than upload speeds. ADSL is faster than ISDN but cheaper than T-1.

AES/EBU. Audio Engineering Society/European Broadcasting Union. A 2-channel digital audio transfer protocol. AES/ EBU is transmitted on balanced XLR connections. Similar in format to S/PDIF, it was intended from the start to be the "pro" format and was never saddled with copy protection (see S/PDIF and SCMS).

AGP. Accelerated graphics port. A special type of interface for PC graphics cards. In a musical context, one advantage of AGP cards is that they don't interfere with audio transfer on the PCI bus, as some PCI graphics cards have been known to do.

AIFF. Audio interchange file format. An uncompressed digital audio file format common on Macs (see WAV).

ASIO. Audio Stream Input/Output. Steinberg's driver protocol for communication between audio hardware and software. It bypasses the operating system's standard multimedia audio drivers to provide multichannel support, improve audio timing, and reduce monitoring latency. The recently released version 2.0 adds sample-accurate positioning, decreased latency, and the ability for multiple applications to share hardware. Although ASIO is not a universal standard, it has been implemented by quite a few major hardware and software vendors (see EASI).

BNC. Bayonet Neill-Concelman. A locking bayonet-style connector used with coaxial cable (see Fig. 1).

DAC (also D/A converter). Digital-to-analog converter. A circuit that translates digital audio information into smoother analog waveforms. A DAC has special filters that interpolate the shape of the waveform between samples to restore its continuously variable analog shape from the disjunct "stepped" shape of its digital representation.

DIN. Deutsches Institut fur Normung. A German standards organization. The most common DIN standard found in the United States is the ubiquitous five-pin DIN plug used for MIDI connections (see Fig. 1).

DLS. Downloadable sound (or sample). A standard for transferring sample data. To overcome the widely varying quality of General MIDI (GM) playback devices, the DLS specification was developed, allowing for some or all of a sound set to be transmitted along with a MIDI file.

DSP. Digital signal processing (or processor). A type of computation optimized for manipulating audio signals. From relatively simple processes such as level changes to complex operations such as vocoding, digital signal processing is the fundamental technology of the desktop music revolution. While DSP is by nature a software process, audio hardware is increasingly incorporating DSP chips. Like a math or graphics coprocessor, these chips are specially designed to perform a limited type of computation efficiently.

DVD. Digital Versatile Disc (originally Digital Video Disc). Similar to the CD format but capable of significantly higher data density. The additional storage allows for high-resolution digital video and multichannel audio. Recordable (DVD-RAM/DVD-R), rewritable (DVD-RW), and audio-only (DVD-A) variants have been defined.

EASI. Enhanced Audio Streaming Interface. Emagic's multichannel alternative to stock multimedia audio drivers. EASI provides a direct and consistent way for audio software and hardware to communicate, resulting in improved audio timing and reduced latency. Introduced in May 1999, it hasn't yet achieved widespread support (see ASIO).

EIDE. Enhanced integrated device (or intelligent drive) electronics. Until recently, the most common disk drive interface on the PC platform. While capable of decent throughput, it was limited to four devices, two of which were commonly the floppy drive and CD drive. Also called ATA-2, its now common successor is UltraATA or UltraDMA, sometimes with a -33 or -66 to specify its bus speed.

FTP. File transfer protocol. A standard for sending and receiving files on the Internet.

HTML. HyperText Markup Language. The basic formatting language for Web pages. It uses simple tags to designate format attributes and allows for "hypertext" links, which allow users to associate a segment of text with another page or other object (see SGML and XML).

HTTP. HyperText transfer protocol. A standard for transferring hypertext files on the Internet. In simpler terms, the behind-the-scenes stuff that goes on every time you expect a Web page to appear in your browser (see HTML).

IEEE-1394. Institute of Electrical and Electronics Engineers standard 1394 (also known as FireWire or Serial SCSI). A very high-speed standard for attaching external devices. It supports the daisy-chaining of multiple devices, making it ideal for external audio disk drives. It's common on Macs but hasn't yet achieved the same popularity for PCs.

ISDN. Integrated services digital network. A high-speed Internet connection using fiber-optic lines (see T-1 and ADSL).

LTC. Longitudinal time code. A common implementation of time code in audio, in which the time code signal is "striped" (recorded) on an analog audio track. Most current digital audio gear is capable of sending and receiving time code through a dedicated connection, rendering LTC striping unnecessary (see SMPTE).

MDM. Modular digital multitrack. A digital tape recorder designed to link easily with others of its type to build a multitrack recording setup eight tracks at a time. MDMs, such as the Alesis ADAT and Tascam DA-88, brought digital multitrack recording within the reach of personal studios, enabling musicians to add tracks as their finances allowed or their needs dictated (see Fig. 2).

MMC. MIDI Machine Control. A set of MIDI commands enabling a device to control other devices. MMC includes such commands as Start, Stop, and Locate but does not provide synchronization information (see MTC).

MMX. Multimedia extensions. A set of 57 instructions incorporated into the third generation of Intel's Pentium chips, designed to facilitate processing of audio and video. Pentium/MMX chips also featured more Level-1 cache and other enhancements, resulting in better performance even for applications that didn't specifically use the new instructions.

MO. Magneto-optical. A format for long-term data storage. Magneto-optical disks represent a compromise between the stability and longevity of optical storage, such as CD and DVD, and the speed and rewritability of magnetic storage, such as hard disk and tape. Newer MO technology approaches the speed of modern hard disks, making it viable for digital recording.

MOD. Module. A type of file containing sampled sounds and a set of musical instructions for playing a song using those sounds exclusively.

MP3. MPEG-1 Layer III (not MPEG-3). The audio compression protocol defined in the MPEG-1 Specification. It uses a perceptual coding scheme to strip away "unnecessary" audio information, resulting in significantly reduced file sizes. Its reputation for excellent fidelity and rapid downloading has made MP3 easily the most successful such method to date, spawning portable MP3 playback devices in addition to creating an enormous popular stir on the Internet (see Fig. 3).

MPEG. Moving Pictures Experts Group. The organization responsible for defining some standards of video and audio compression that have proven useful in multimedia applications. The MPEG-2 audio specification pairs CD-quality audio with video suitable for broadcast or DVDs (see MP3).

MTC. MIDI Time Code. A form of time code transmitted over MIDI connections. MTC is useful for synching devices, but its resolution is too coarse to ensure sample-accurate positioning (see SMPTE).

PCI. Peripheral component interconnect. The standard interface for internal devices, such as modems and audio cards. Its adoption by both major platforms has led to a number of crossplatform audio devices. A "local bus" interface, it can redirect data without passing it through the CPU, making it much quicker than previous designs.

PCMCIA. Personal Computer Memory Card International Association. A credit-card-size interface commonly found in notebook computers. Type III devices use the same connectors as Type II but are twice as thick. Primarily used for modems and network interfaces (and for storing programs in synthesizers), the PCMCIA specification historically has been inhospitable to audio devices. A handful of successful devices do exist, however. The current preferred term is PC Card, and a 32-bit implementation is called CardBus (see Fig. 4).

RAM. Random-access memory. A computer's high-speed short-term memory. Data and code are read from a disk or other "permanent" storage device into RAM, which passes it back and forth to the CPU for processing. RAM can't retain data without power, so files must be saved back to disk for storage. Various types of RAM include SRAM (static RAM), DRAM (dynamic RAM), SDRAM or SyncDRAM (synchronous DRAM), and EDO RAM (extended data out RAM).

RCA. Radio Corporation of America. The familiar pin-and-collar connector used with most consumer audio gear, developed by RCA. Commonly used for unbalanced line-level connections or with coaxial cable for S/PDIF connections. Also known as a phono plug (see Fig. 1).

RMF. Rich Music Format. A type of MIDI file developed by Beatnik, Inc., designed to be played back with its Beatnik Player. The player incorporates a custom sound set and allows for additional sounds to be embedded in the file, enabling greater control over playback than you have with the GM specification alone.

ROM. Read-only memory. A type of memory chip that can be read but not changed. ROM is found in keyboards as well as computers and is typically used to hold wavetable data in sound cards or low-level instructions, such as a computer's BIOS.

S/PDIF. Sony/Philips digital interface format. A 2-channel digital audio transfer protocol. S/PDIF connections are made via RCA connectors on coaxial cable or via fiber-optic cable (see TOSLINK). Similar in format to AES/ EBU, technically it must carry antipiracy code (see SCMS), limiting its resolution. Most current implementations ignore the copy protection and transfer a full 24-bit word. If you see "SDIF," it's not a typo-it's Sony's own "professional" digital audio transfer format, which also uses coaxial cable but with BNC connectors.

SCMS. Serial copy management system. An antipiracy scheme built into "consumer" digital audio transfer devices, namely those in S/PDIF format. Flags hidden in the data stream are read by special circuits in consumer digital recorders, allowing the user to make only first-generation copies, never copies of copies. Since the DAT format never caught on with consumers, SCMS has been largely ignored (see S/PDIF).

SCSI. Small computer systems interface. A standard for computer input and output. Historically, SCSI is the preferred interface for hard disk recording systems, as it provides high data-transfer rates and supports up to seven drives. While SCSI ports were standard on Macs for a long time, the format was reserved for high-end applications on PCs due to its well-founded reputation for being difficult to set up. Different "flavors," differentiated by bandwidth and speed, include SCSI-2, UltraSCSI, Fast/Wide SCSI, and the current state of the art, SCSI-3 (see EIDE and IEEE-1394).

SDS. Sample Dump Standard. A method of transferring sample data through a MIDI connection. Because of the large amount of data contained in sampler banks and the relatively low bandwidth of MIDI connections, SDS can be a tedious way to transfer data. SMDI (SCSI musical data interchange), which requires both SCSI and MIDI connections, is much faster.

SGML. Standardized general markup language. An ISO standard for electronic documents. SGML is more complex and powerful than HTML (see HTML and XML).

SMPTE. Society of Motion Picture and Television Engineers. SMPTE time code, often referred to simply as SMPTE, is used to communicate timing and positioning information among audio (and video) devices. SMPTE uses the format hours:minutes:seconds:frames (HH:MM:SS:FF) to specify locations (see LTC, MTC, and VITC).

T-1. A very fast type of Internet connection capable of moving a megabyte of data in less than 10 seconds (see ISDN and ADSL).

TDIF. Tascam Digital Interface. Tascam's format for transferring eight channels of digital audio over shielded cable with 25-pin D-Sub connectors. TDIF and ADAT Lightpipe are the two most common multichannel digital audio transfer protocols.

TDM. Time Division Multiplex. Digidesign's proprietary plug-in architecture. Based on technology developed by Bell Labs, TDM plug-ins run on the dedicated engines of Pro Tools DSP Farm cards (see DSP).

TOSLINK. Toshiba Link. A fiber-optic alternative to coaxial cable for S/PDIF transfers.

TRS. Tip-ring-sleeve. An audio connector used for stereo, balanced mono, or send-return connections. Similar to TRS, the TS (tip-sleeve) connector is used for mono connections, such as plugging a guitar into an amp (see Fig. 1).

URL. Uniform resource locator. The standard format for identifying sites on the Internet. It's the ".com" string of address gibberish that went from geeky to trendy in less than two years.

USB. Universal serial bus. A medium-speed serial interface for connecting external devices. Not nearly as fast as SCSI but faster than common serial ports, USB's ease of use, support for multiple devices, and rapid adoption by both major platforms has already led to the development of crossplatform USB devices. Common uses of USB include scanners, digital cameras, MIDI interfaces, and stereo digital or analog audio interfaces (see Fig. 5).

VITC. Vertical interval time code. The common implementation of time code for video. Timing information is contained in the "vertical blanking interval," the area between frames in which there is no video information (see SMPTE).

VST. Virtual Studio Technology. Steinberg's plug-in architecture.

WAV. Not an acronym: an abbreviation for "wave" or "waveform." An uncompressed digital audio file format, common on PCs, that was jointly developed by Microsoft and IBM (see AIFF).

XLR. Not an acronym but a part number (and trademark) for a circular three-pin connector created by Cannon. It became the standard connector for balanced analog and digital audio and is now used as a generic term (see Fig. 1).

XML. Extensible markup language. A W3C (World Wide Web Consortium) standard for electronic documents. XML is a simplified version of SGML (see HTML and SGML).

Brian Smithers is a musician, conductor, and arranger at Walt Disney World. His Web site ( covers making music with notebook computers.