D

Damping Factor

Technically, the damping factor of a system refers to the ratio of nominal loudspeaker impedance to the total impedance driving it (amplifier and speaker cable). In practice, damping is the ability of the amplifier to control speaker motion once signal has stopped. A high damping factor means that the amplifier's impedance can absorb the electricity generated by speaker coil motion, stopping the speaker's vibration.

Other points:

1. Damping varies with frequency. Some manufacturers publish a damping curve for their amps.
2. The effects of damping are most apparent at low frequencies, in the range of the woofer's resonance. Well damped speakers sound "tighter" in the low end. Low damping factors result in mushy or indistinct bass.
3. Speakers connected in series or parallel will experience the same damping factor from the amp. Impedance determines damping factor, not speaker wiring.
4. Higher impedance speakers increase system damping factor.
5. The damping factors you see published as amp specs are for the amp only, not referenced to an entire system. Higher is better, and you'll often see quite high numbers, 200, 300, even 3000 or higher.
6. System damping factors over 10 are generally acceptable. The higher the better.
7. For the tweaky among you, here's how to calculate a system's damping factor: First, calculate the output impedance of the amp into, say, an 8 ohm speaker (use the nominal impedance of whatever speaker you are using for your own calculations), and a 100 foot 12 gauge speaker cable. Let's also say we have an amp with a published damping factor of 3000. Since damping factor is the ratio of speaker impedance to amp output impedance, you can work backwards, dividing 8 by 3000, giving us .0027 ohms amp output impedance. You must also consider the impedance of the speaker cable; 12 gauge wire is in the range of .0016 ohms/foot (cable catalogs sometimes publish this spec). For a 50 foot speaker cable, you've got 100 "feet" of impedance (50' out, 50' back) giving a total cable impedance of around .16 ohms (note this is much higher than the amp's impedance - one reason larger speaker wire is better for long runs!). This makes the total output impedance .1627 - pretty low. The system damping factor will then be 8 ohms divided by .1627, resulting in a very good score of 49.

DASH

Another music industry acronym. DASH stands for Digital Audio Stationary Head and pertains to a format of digital recorders. Back in the days when digital recording was in its infancy it was not yet clear whether most recorders would use rotating heads (like DAT machines) or stationary heads. Early on DAT was called R-DAT for just this reason. There was also S-DAT, but it was far less used in favor of the DASH acronym that was already in use (and because stationary head DAT machines never got off the ground). Most of the real high-end digital audio multitrack machines (those made by the likes of Sony and Mitsubishi) are DASH machines. These big machines use a reel of special digital tape that runs past a stationary head at (relatively) high speeds. They look almost like analog reel to reel machines to the uninitiated, but generally cost three or four times as much money.

DAW

Pronounced "Dee - A - Double-U", the abbreviation (not acronym) for Digital Audio Workstation. DAW's are common in almost any studio these days. They are typically defined as having some ability to record, manipulate, and play back audio recordings or samples. In their early days DAW's were primarily considered editing stations. Material was taken from the primary recording media (usually tape) and dumped into one of these systems for editing, and then returned to the original media for the remainder of the project. Nowadays DAW's can act as an entire recording studio with all mixing, processing, and mastering on one computer.

dB

Abbreviation for Decibel. It literally means one tenth of a bel. The bel is a unit of measurement named after Alexander Graham Bell. The bel had its origin in the Bell Telephone Labs, where they needed a convenient way to express power losses in telephone lines as power ratios. Because the bel is a power ratio of 10, and this is a rather large ratio, it is convenient to divide it into tenths of bels, or decibels. Decibels are used all over the place in audio measurements and specifications partly because it is very easy to express extremely large or small values with decibels due to their logarithmic nature. The full depth of the topic is well beyond the scope of this writing (we will cover more in the future), but suffice to say that the decibel always refers to a ratio of two values. It is never an absolute value. Thus when we speak of losses and gains in audio we use dB to quantify those values. If a signal goes into a unit and is output at a lower level it is said to be down by some value of dB. Decibels come in many variants: dB PWL, dB SPL (also known as Sound Pressure Level), dBm, dBu, dBV, dBv, and more.

dbx

dbx is a company who is most known for their history of building dynamics processors. In fact they developed the modern VCA that made high quality dynamics processing possible. But their name has also been somewhat synonymous with noise reduction. Like Dolby, the term dbx is often used generically to mean noise reduction. Dbx noise reduction systems work in a way that is fundamentally different from the early Dolby systems. They use compression (to tape) and expansion (from tape) of the audio to lower the relative noise levels and effectively double the dynamic range. The systems work well, but like Dolby, have side effects that some users find unacceptable for modern high quality recording. The development of these systems has slowed in recent years and they have pretty much fallen out of favor with professional recording engineers. There are two main types (type 1 and type 2) that we will discuss in the next few days.

dbx Type I

A noise reduction scheme developed by dbx. Many people refer to any and all dbx noise reduction processes simply as dbx. Type 1, however, is the specific name for the type of dbx found in the higher end recording systems and stand alone encoder/decoder systems. It is designed specifically for high bandwidth media such as modern multitrack recordings. Although simple in theory, the classic 2:1:2 compander noise reduction used in the Type 1 could not be practically achieved before the development by dbx of two patented circuits, the dbx RMS detector and dbx Voltage Controlled Amplifier (VCA). The RMS detector enables optimum decode tracking and transient response despite the phase shifts typically induced by tape recorders. The dbx VCA provides precise gain control over an extremely wide dynamic range while maintaining very low noise and distortion.

dbx Type 2

A noise reduction system made by dbx. Type 2 (normally written Type II) is very similar to dbx Type 1 noise reduction, but has greater pre-emphasis to the high frequencies allowing high quality recording to be achieved on limited bandwidth media such as cart machines, linear video tracks, telephone lines, and numerous other technologies.

DC Offset

DC offset is an imbalance that sometimes occurs in A/D converters (see WFTD archive "A/D Converter"). When working with audio is it desirable to have only the audio program material passed through the signal path. Almost by definition audio, being a periodic waveform, is an AC (Alternating Current) signal. DC (direct current) is of the non alternating or periodic variety and thus has no constructive purpose as part of an audio signal. It is merely a constant voltage that is present which can eat up headroom (see WFTD archive "Headroom") and cause clicks and pops during editing.

DDS

An abbreviation for Digital Data Storage. DDS is a data storage format which was developed from DAT (Digital Audio Tape) by Hewlett-Packard and Sony, especially for reliably storing computer data. DDS is defined by international standards and is supported by many manufacturers, but more importantly, it is subject to thorough collaborative testing programs which ensure that tapes written by one maker's drives can be read by those of other manufacturers.

DDS drives are rigorously tested for format compliance and data interchange according to a scheme that Hewlett-Packard administers. DDS media is put through a comprehensive set of tests designed to ensure that only data cartridges capable of meeting the exacting environmental and durability requirements of the DDS standards bear the DDS trademark. This scheme is administered by Sony.

Decay Time

The time it takes for the sound pressure level of reverberations to drop in level by 60 dB (one millionth) from their original strength. This is sometimes also called "reverb time." Carefully setting the decay time allows you to have the mix be as "wet" as you desire, without making things muddy or unclear...

Decca Tree

A stereo miking technique. A Decca Tree configuration is characterized by having three omnidirectional microphones in a "T" shaped setup. Two of the microphones are positioned about two meters apart. The third microphone is positioned between the first two, but about 1.5 meters forward (closer to the source) of them. This configuration is sometimes used for orchestral recordings and film scoring due to its natural sound with good separation. It is useful in film because the image doesn't usually cause problems with Dolby or other surround processes. In many cases the Neumann M50 (or now, the newer TLM50) is used as the center microphone because of its unique directional characteristics and smooth sound.

Decibel

We've all used the term "decibel" hundreds of times, but what does it REALLY mean? A decibel (named for Alexander Graham Bell) is a tenth of a bel, and is used as an expression of power. Here's where the confusion arises: A decibel isn't a measure of ANYTHING; it is a ratio of two power levels. Because of the way our ears perceive volume, these ratios follow a logarithmic curve, expressing them as a decibel keeps things easier to deal with. Here are a few convenient decibel figures worth remembering: One decibel is commonly taken as the smallest volume change the human ear can reasonably detect. Doubling the POWER of an amplifier results in a 3 dB increase, which is a "noticeable" volume increase. Doubling the VOLUME of a sound is a 6 dB increase (you may occasionally see 10 dB listed as the "double-volume" figure, 6 dB is the more mathematically correct number). By doing the math, you can see that truly doubling your volume actually requires 4 times the amplifier power! Keep these figures in mind the next time you are comparing the specs of two pieces of equipment...

Demagnetizer

A device for removing magnetism from the heads and metal tape path components of tape machines. When magnetic (magnetized) tape passes across these metal parts it tends to magnetize them as well. In general, this is not a good thing! When these parts become magnetized they tend to degrade the signals recorded and played on subsequent tape passes through the transport. Notably, high end may be compromised, signal levels can be reduced, and so on. Opinions vary as to how often a machine should be demagged; some fanatical engineers have been known to demag after each pass of tape - we don't recommend getting quite THAT carried away! Check your tape machine's documentation for its manufacturer's recommended maintenance schedule. In most cases if the machine is being used fairly heavily, we recommend demagnetizing once a month or so.

Differential

In the computer world, a "balanced" signal is known as "differential". The same technique is used - the signal is sent with the inverse signal running parallel to it. Sometimes, the two signals' wires are twisted around each other (known as "twisted pair" wire). Differential signals are used in 10Base-T and 100Base-T Ethernet and some varieties of SCSI.

(Special thanks to inSync reader, David C. for this one.)

DIN

An acronym for Deutsche Industrie Normung (also seen as Deutsche Institute fur Normung and Deutsche Industrie Norm), DIN is a German organization that establishes standards for industry. One common place you'll encounter DIN standards in America is with circular multi-pin plugs, like those found on the ends of MIDI cables. Other DIN standards exist, including noise specs, rack measurements, signal EQ standards and more. It is important to note that they do not necessarily match up with the corresponding American standards.

Din Stereo

A stereo recording technique where two cardioid microphones are spaced 20 cm and angled 90° creating the stereo image. This is remarkably close to an ORTF configuration. The DIN stereo produces a blend of intensity between stereo signals and time delay stereo signals, due to the off-axis attenuation of the cardioid microphones together with the 20 cm spacing. If used at larger distances to the sound source the DIN stereo technique will loose the low frequencies due to the influence of the proximity on these types of microphones. The DIN stereo technique is more useful at shorter distances, for example on piano, small ensembles or used for creating stereo on an instrument section in a classical orchestra.

Direct Box

Often abbreviated DI (for direct insertion), a device commonly used to convert high impedance (see WFTD archive Impedance) unbalanced signals from a stage instrument (like a bass or keyboard) into a low impedance balanced signals. This puts the signal at the proper voltage level for the mixer and prevents the instrument from becoming loaded down with too low impedance, which could cause tonal shifts and distortion. It also allows the signal to be transmitted over long lengths of cable. They are always used in live sound to get a signal out of an instrument on stage out to the mixing board, which can be as much as 500 feet away. A simple direct box consists only of a small transformer, but more sophisticated designs employ electronic gain stages that more closely resemble the input section of a modern instrument amp. They may also have some combination of ground lift switches, equalization switches, level matching switches, isolated line outputs, and more.

Direct I/O

The trademarked name for Digidesign's software drivers that allow programs such as audio sequencers from various companies to directly access Digidesign audio hardware installed in a computer. Without Direct I/O drivers most audio programs can only interface with the Apple's built in audio, which can then often be interfaced with the hardware-recording card. The disadvantage is that this only allows for two channel input and output because that is all the computer supports. Direct I/O gives the software the ability to directly interface with multi-channel hardware, such as Digidesign's Pro Tools and Project systems, thereby allowing multiple inputs and/or outputs to be used simultaneously. Direct I/O drivers have to be specifically written for each hardware type. Most of the popular audio sequencer manufacturers (MOTU, Opcode, EMAGIC Steinberg, etc) have written their own Direct I/O drivers that work with Digidesign hardware and hardware from other companies.

Disc-At-Once

A method of writing red book audio CD's. Disc-at-once, as opposed to track-at-once and other methods, writes the entire CD in one pass. That is the laser never turns off once the writing has begun. This is significant because it is the only way to produce an audio disc suitable for mass duplication. If the laser turns off for any reason while burning a disc it creates a small inconsistency in the reflective material that is interpreted by CD mastering machines as a fatal error. The CD is still entirely playable on most CD players, but the machines at the mastering house will kick it out. If you are making audio CD's for mass duplication you need to make sure your hardware and/or software supports and is set to use disc-at-once mode. Nowadays most systems default to this when writing audio CD's.

Dispersion

The angle of effective coverage for sound radiated from a speaker. When looking at speaker specifications, you'll see this listed with two components, horizontal and vertical (i.e. 90 degrees x 60 degrees).

Distribution Amplifier

A Distribution Amp, or DA, is a low power amplifier designed to transparently split an input signal to several outputs. For example, the stereo outputs of a mixing console might be run to a DA, where they would be split to simultaneously feed a cassette deck, a DAT recorder, a CD recorder, and so on. Using a distribution amp prevents various problems caused by passively splitting ("Y"-ing) an output to feed multiple sources.

Dither

Literally, dither is noise added intentionally to a digital recording. Low level signals are difficult for digital gear to record; the sampling machine simply has difficulty deciding whether the necessary bits should be turned on or off, creating "quantization noise." By adding a small amount of very controlled noise to the original signal, the bits can be made to positively switch on or off, improving low level sound resolution. The noise used is often "shaped" to be in-offensive to human ears. Good dithering algorithms, whether hardware or software based, can make an incredible difference in the sound quality of a digital recording!

Divergence

A term used in surround sound mixing. When left, right, and center channels are available, a sound can be placed in front of the listener by mixing it entirely to the center channel, or by splitting it equally between the left and right channels. Compared to sending the track directly to the center channel, mixing the track to the left and right channels creates the impression of an extended sound source. Whether a narrow or wide source is desired depends on the situation, and many surround panners provide a so-called divergence control, which adjusts the left/center/right panning parameters to control the portion of front-placed sounds mixed to the center channel.

Diversity Receiver

In wireless microphone applications, diversity receivers are often used to improve reception of RF signals. A diversity receiver utilizes two separate, independent antenna systems. The receiver looks at the signal coming in from the each antenna, and determines which one is the stronger. It then switches to that stronger signal. The receiver is constantly comparing to see which antenna is providing the better signal, and can quickly switch from one to the other as signal strength changes.

Dolby

Short for Dolby Laboratories, this word is often used to generically refer to noise reduction, for which they are famous. Dolby Labs was founded in 1965 when they developed their first noise reduction systems. Since then they have been a huge contributor to the betterment of recorded sound with many advancements in technology. Today they are known for noise reduction systems, stereo and surround sound encoding technologies, recording headroom extension, and many developments for theatre film sound reproduction and digital media sound reproduction. We will cover more of the specific Dolby formats in the future.

Dolby A

The first noise reduction process developed by Dolby Labs. Introduced in 1965, it was designed for use by professional recording studios to make quiet master tape recordings. In the early to mid 1970's its use was extended to film recording studios and motion picture release prints in order to make films sound better. Almost every recording studio making analog master tapes, whether for film or strictly audio applications, will have A-type equipment manufactured by Dolby Laboratories.

Dolby B

Dolby B-type noise reduction, providing about 10 dB of noise reduction at high frequencies, was a simplification of A-type that was introduced in 1968. It worked by boosting high frequencies on recording them and then reducing them (and recorded noise) upon playback. It extended the use of Dolby technology into the consumer environment, giving consumer electronic companies the ability to make cassette tapes and players, which gave the consumer quiet recordings. Dolby makes professional B-type encoding equipment that is sold to tape duplicators, allowing them to make consumer B-type encoded cassettes. In addition, the technology is licensed to consumer hardware manufacturers, giving them the ability to purchase Dolby B-type integrated circuits (ICs) from various semiconductor manufacturers and then build cassette decks, portable players, car units, etc., which can record and/or playback cassettes with B-type encoding.

Dolby B has become a maligned form of noise reduction in the past 20 years because so many users have reported a loss of high frequency content on playback with it. While there are more sophisticated forms of noise reduction available today, Dolby B does have a bit of a bad rap. Most users who had problems with it did so because they recorded to close to the saturation level of their tape. The tape then had no available headroom in the high frequency range where the boost occurred and thus, upon playback the highs, which were cut as if they had been boosted, ended up being rolled off too much and the resulting tapes sounded dull. A common work around for this problem was to record tapes with Dolby B and play them back without it. Of course this defeated the noise reduction aspect of it, but many users liked the high-end boost as well as the smooth high frequency tape saturation on their tapes. When used properly Dolby B actually works quite well.

Dolby C

Dolby C-type noise reduction, introduced in 1981, was Dolby's second generation consumer system -- basically doubling the amount of noise reduction that Dolby B-type provided, while having fewer negative side effects by adding other technological features such as spectral skewing, anti-saturation, etc. It is licensed to dozens of electronic companies and found on almost every modern home cassette deck and on high-end portable tape players as well.

Dolby Digital

Also known as AC-3, Dolby Digital is an advanced perceptual coding technology for transmission and storage of up to five full-range channels (Left, Center, Right, Left Rear, Right Rear), plus a supplemental bass-only effects channel (referred to as a .1 channel due to the smaller number of bits needed for the information). It accomplishes this in less space than is required for one linear PCM coded channel on a compact disc. Dolby Digital is a more powerful and flexible coding system than AC-2 and provides a feature set including: 1) down mixing for optimal reproduction in mono, stereo, and Dolby Pro Logic compatible configurations as well as full 5.1 channel sound; 2) carriage of dynamic range and dialog level control information to decoders; and 3) operation over a wide range of bit rates. Dolby Digital can be heard on the soundtracks of a thousand plus films, and on the current generation of laser discs. Dolby Digital is being used on the audio tracks on DVD, and will be the standard audio on the new high definition television (HDTV) system going into operation in the United States.

Dolby HX Pro

Dolby HX Pro was introduced in the early 1980's and provides high frequency headroom extension for analog tape recordings. Because it has the Dolby name and is included in most modern tape recording machines many people have erroneously assumed it is a noise reduction system, which it isn't. It dynamically adjusts the record bias level to counteract a phenomenon known as "self biasing" that can take place when recording hi frequencies to analog tape. The result is greatly improved headroom, which can be used to record at higher levels thus improving the signal to noise ratio. HX Pro is found on all sorts of mid-level professional and consumer recording machines these days. It is a record only process (no decoding is required) so most machines have it "on" all the time with no way to turn it off. Since few, if any, negative side effects have ever been reported from using HX Pro most people are happy to use it on machines that are so equipped.

Dolby Pro Logic

Dolby's second generation licensed home surround system. A major advantage of Dolby Pro Logic over the preceding system (Dolby Surround) is the use of an active center channel with its own speaker. Conventional stereo systems create a phantom center channel, which is effective for viewers seated directly in front of the television screen. However, for viewers seated off center, the dialog can appear to come from off center. But with Dolby Pro Logic and the use of an appropriately placed center channel loudspeaker, the dialog always appears to come right from the screen, allowing the main left and right stereo speakers to be widely spaced for a good spread on music and effects. Dolby Pro Logic decoders also decode surround information which is typically fed to a pair of surround speakers slightly behind and to the left and right of the listener.

Dolby S

The consumer version of Dolby SR noise reduction. Dolby S-type noise reduction was derived from Dolby SR, and shares with it such developments as combining both fixed and sliding bands, anti-saturation, spectral skewing and modulation control. As a licensed technology (although Dolby makes professional S-type encoding equipment), it provides 24 dB of noise reduction at high frequencies and 10 dB at low frequencies. Modern high-end cassette decks generally contain Dolby S-type and give the home consumer the ability to make cassette tapes that sound like nearly as good as CD's.

Dolby SR

Dolby SR (SR is the abbreviation for Spectral Recording) was introduced in 1986 as Dolby's second generation professional recording system. Not only was it designed to provide more noise reduction than past systems, but it also provided a number of other technological innovations that extend the recording's dynamic range and allowed a very high quality master recording (very nearly digital). Thus SR is referred to as a signal processing system rather than just a noise reduction system. SR arrived on the scene not long after some of the first high-end digital machines appeared and it was instrumental in keeping analog recording viable at a time when everyone wanted the noiseless (if antiseptic) sound of digital recording. Just about every serious studio with a 2" 24-track had an SR rack next to it. SR never found its way into consumer recording machines due to the extreme cost of the electronics and due to sensitive calibration issues.

Dolby Stereo

After introducing the use of Dolby A-type noise reduction to the film industry, Dolby's next major contribution was Dolby Stereo. This contribution allowed movie makers to put 4 channels (hmm... most people call that quad) of sound information on motion picture release prints using matrix technology, and gave theaters the ability to replay this 4-channel format for the movie going public. The four channels were actually left, right, center, and surround. This was the precursor to (and actually the theater version of) what became known as Dolby Surround.

Dolby Surround

Dolby Surround is an early home embodiment of Dolby Stereo. Video production companies are licensed to make VHS tapes and laserdiscs that contain the same 4-channel matrix encoded information that was contained on the original motion picture release. Consumer electronic companies are licensed to make consumer surround decoders that reproduce these 4 channels in the home. It has a passively derived center channel and is not to be confused with Pro Logic, which we will cover soon.

Dongle

An electronic device that attaches to a computer to control access to a particular application. Dongles provide an effective means of copy protection. Typically, the dongle attaches to a PC's parallel port or, on a Mac, to an ADB port. Ideally a dongle passes through all data coming through the port so it does not prevent the port from being used for other purposes. In fact, it's possible to attach several dongles to the same port. Programs that use a dongle query the port at startup and at programmed intervals thereafter, and terminate if it does not respond with the dongle's programmed validation code.

Doppler

The Doppler effect, named after a German physicist (how come things are always named after a German physicist?), is the apparent change in pitch of the sound that occurs when the source of the sound is moving relative to the listener. For example: A car horn will sound higher in pitch as it approaches, and lower in pitch after it passes us. This is one principle that is employed in a rotating speaker system like a Leslie. The rapid movement of the horn to and away from the listener creates a sort of vibrato effect. There are many modern effects units that simulate the Leslie sound, and also offer other types of Doppler effects.

If a loudspeaker is producing both low and high frequencies, the low frequencies will cause the cone to move alternatingly toward and away from the listener (obviously high frequencies do this too, but the lows are much more pronounced). As this is happening the perceived pitch of the higher frequency sounds rise and fall at a rate (or rates) equal to the low frequencies moving the cone. This is actually Frequency Modulation of the high frequency by the low frequency, and is called "Doppler Distortion." It manifests itself as a sort of "muddiness" (subjective audio term #108) of the sound.

Double System Sound

A method of producing sound motion pictures where the sound track is recorded on a magnetic tape recorder that is synchronized with the movement of the film in the camera. The synchronization is done by recording a special tachometer signal on one track of the tape. This signal is generated by the camera and is at 60 Hz when running at 24 f.p.s (the standard frame rate for film). When the tape of the sound track is played back, the sync signal is sensed by a device called a resolver, which adjusts the speed of the tape player to match the speed of the movie projector.

Double Tracking

The process of recording a track, then recording a second track while listening to the first and duplicating it. When the two tracks are played back together, the result is a slight "chorusing" and fattening of the signal due to minor pitch and timing differences between the two performances. Double tracking is an effective tool, and has been used extensively in most pop music styles. Vocals, melodic parts, rhythm guitars, and solos are common candidates for doubling, tripling or even more (you can never have too many rhythm guitar tracks in our opinion).

Dreadnought

A term used to describe large sized acoustic guitars that were known for their formidable volume and booming bass. While considered a generic term today, the Dreadnought guitar was an original creation of C. F. Martin & Co. The very first Dreadnought guitars (named for a class of World War I-era British battleships, "Dreadnought") were manufactured by Martin for the Oliver Ditson Company, a publishing firm based in Boston that was also a leading music retail chain in the area. The Ditson Company went out of business in the late 1930's, and Martin incorporated the Dreadnought into its line of guitars. Today, the model is a dominant factor in the Martin line, and every maker of acoustic guitars, both domestic and foreign, has introduced a version of the original Martin design.

Driver

In the world of computers, a virtual road map exists that tells data for each piece of equipment or program which path to take to its chosen destination. Just like in the real world, you need directions on how to get from A to B. In the world of computers, we call those devices "drivers". Drivers are bits of software code used to enable various pieces of hardware and software so they can be recognized by other programs in a computer and have the appropriate data routed to them in a format they can understand. For example, Windows uses drivers to communicate with a MIDI interface. If you do not have the proper driver installed your computer may not recognize or work properly with a given piece of hardware or software.

Drop Frame Time Code

The method of time code computation that accounts for the reality of there being only 29.97 frames per second in color NTSC video. The .03 frame is visually insignificant, but mathematically very significant. A one-hour video program will have 107,892 frames of video (29.97 frames per second x 60 seconds x 60 minutes). Using a standard non-drop type of time code would cause cumulative errors in synchronization over time. The drop frame time code method of accommodating this reality was developed, where 2 frames are dropped from the numerical count for every minute in an hour, except for every 10th minute when no frames are dropped. This allows any device syncing to color video to be able to stay in nearly exact sync over long periods of time.

DSP

Abbreviation for Digital Signal Processing. This term gets thrown around all over the place these days without much regard for what it actually means. Without getting into a lot of detail it basically just refers to a specific type of digital processing that is optimized for dealing with signals. In our case these are often audio signals, but they don't always have to be. DSP can be thought of as sort of a subset to the old math coprocessor concept. Math coprocessors were chips that were included in computers to help the CPU do massive calculations more efficiently. DSP chips are designed and optimized to be able to do various (mathematical) calculations for processing audio or image data. For example, many of today's effects processors use a special DSP chip made by Motorola that has been optimized for working with audio data. A surprising number of different processors use this exact same chip, but with different software instructions as written by the companies to have it do what they need for their product.

D-Sub

D-Sub and DB are prefixes used to describe a type of multi-pin connectors that happen to be commonly used in audio equipment. The original manufacturer, ITT Cannon, adopted the "D" designation as the lead character in their part numbers signifying the connector type. The shell size, or capacity, is next in the part number: A=15 pin, B=25 pin, C=37 pin, D=50 pin and E=9 pin (not originally produced). This type connector can also be specified with many different styles and quantities (up to its capacity) of pin: high power, coax and combinations. The most common connector, early on, was the 25-pin size, which was used on RS232 ports (a common computer port). Hence DB25M means "D" type, "B" shell, 25 pins, Male pin. Note that a 15-pin female would be DA15F. D-Sub is short for the current industrial tag, D-Subminiature, used by almost all of the manufacturers.

Dub

Making a copy of a recorded tape is called dubbing, and the resulting copy is know as a "dub".

DVD

Latest info says "DVD" no longer stands for anything! It used to mean "digital versatile disc" - and before that it meant "digital video disc." A new type of 12-centimeter (4.72") compact disc (same size as audio CDs and CD-ROMs) that holds 10 times the information. Capable of holding full-length movies and a video game based on the movie, or a movie and its soundtrack, or two versions of the same movie - all in sophisticated discrete digital audio surround sound. The DVD standard specifies a laminated single-sided, single-layer disc holding 4.7 gigabytes, and 133 minutes of MPEG-2 compressed video and audio. It is backwards compatible, and expandable to two-layers holding 8.5 gigabytes. Ultimately two discs could be bounded together yielding two-sides, each with two-layers, for a total of 17 gigabytes. There are three versions: DVD-Video (movies), DVD-Audio (music-only) and DVD-ROM (games and computer use). The DVD-Audio standard is still being defined. Meanwhile a fourth member has joined the family: DVD-RAM defines specs for a rewritable system, opening the door for recording.

Dynamic (Microphone)

A dynamic mic is one in which audio signal is generated by the motion of a conductor within a magnetic field. In most dynamic mics, a very thin, light, diaphragm moves in response to sound pressure. The diaphragm's motion causes a voice coil which is suspended in a magnetic field to move, generating a small electric current. Generally less expensive than condenser mics (although very high quality dynamics can be quite expensive), dynamics feature quite robust construction, can often handle very high SPLs (Sound Pressure Levels), and do not require an external power source to operate. Because of the mechanical nature of their operation, dynamic mics are commonly less sensitive to transients, and may not reproduce quite the high frequency "detail" other types of mics can produce. Dynamic mics are very common in live applications. In the studio, dynamics are often used to record electric guitar and drums.

Dynamic Range

The dynamic range of a sound is the ratio of the strongest, or loudest part to the weakest, or softest, part; it is measured in dB (see WFTD archive "Decibel"). AN ORCHESTRA MAY HAVE A DYNAMIC RANGE OF 90 DB, MEANING THE SOFTEST PASSAGES ARE 90 DB LESS POWERFUL THAN THE LOUDEST ONES.

Dynamic range in audio equipment specifications is often confused with signal-to-noise ratio. Where signal-to-noise ratio is widely considered to be the available range between the normal operating level of a device and its noise floor, the dynamic range is the maximum range available, which would imply it is the range from the highest level attainable in a unit down to the noise floor. With analog systems dynamic range specs can be a moving target since it is known that in analog devices the onset of distortion is gradual. Defining a "maximum" level amidst onsetting distortion has not really been standardized in our industry, though most consider 1% to 3% distortion to be acceptable for this measurement. That means the dynamic range of an analog device can be thought of, unless otherwise specified, as the range between the noise floor and the maximum level attainable without going over 1% to 3% distortion.