- 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


Delay
The time difference between a sonic event and its perception at the listening position (sound traveling through space is delayed according to the distance it travels). People perceive spaciousness by the delay between the arrival of direct and reflected sound (larger spaces cause longer delays).

Diaphragm
The part of a dynamic loudspeaker attached to the voice coil that moves and produces the sound. It usually has the shape of a cone or dome.

Dielectric
Insulating materials exposed to electric fields are called dielectrics. Dielectrics are necessary parts in the construction of any cable because they prevent oxidation and keep the conductors from touching one another. In audio cables, relatively low voltage and current levels mean that dielectric strength is not the most important factor. Far more significant in its effect on the sound is a material's dielectric absorption. This characteristic describes the way a dielectric may discharge a secondary signal into the conductor out of phase with the audio signal.

As a current is passed through a conductor, an electromagnetic field is created which interacts with the dielectric material and temporarily displaces the molecular structure. If the dielectric material has good elasticity and can return quickly to its normal state, then the material is said to have low dielectric hysteresis or loss and will have little audible effect on the signal.

Diffraction
The re-radiation of sound waves at discontinuities such as cabinet edges. The time-delayed wave interferes with the original sound output, causing peaks and dips in the frequency response and smearing the transient response.

Diffusion
In audio, the scattering of sound waves, reducing the sense of localization. In video, the scattering of light waves, reducing hot spotting, as in a diffusion screen.

Diffusor
Acoustical treatment device that preserves sound energy by reflecting it evenly in multiple directions, as opposed to a flat surface, which reflects a majority of the sound energy in one direction.

Digital
Represented by a numerical code. For sound, the conversion of an analogue waveform to a series of numbers representing the instantaneous amplitude for each sample taken, the storage of those numbers, and the eventual conversion back to analog format for replay.

Digital Dolby
An encoding system that digitally compresses up to 5.1 discrete channels of audio (left front, center, right front, left surround, right surround, and LFE) into a single bitstream, which can be recorded onto a DVD, HDTV broadcast, or other form of digital media. When RF-modulated, it was included on some laser discs, which requires an RF-demodulator before the signal can be decoded. Five channels are full-range; the .1 channel is a band-limited LFE track. A Dolby Digital processor (found in most new receivers, preamps, and some DVD players) can decode this signal back into the 5.1 separate channels. Most films since 1992's Batman Returns have been recorded in a 5.1 digital format, though a number of films before that had 6-channel analog tracks that have been remastered into 5.1.
(Dolby Digital and Pro-Logic are registered trademarks of Dolby Laboratories Inc.) (See also AC3)

Dipole
Speakers with drivers on opposite faces that are wired electrically out of phase, creating an area of cancellation to the sides. Recommended by THX for use as surround speakers, with null directed at the listener to create a more ambient and non-localizable effect.

Direct View Television
Display whose image is created on the surface from which it is viewed.

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

Dispersion Modifier
Center bullet in a midrange driver in place of a conventional dust cap. It improves dispersion in the mid-frequencies, and helps to maintain the high frequency response of midrange units.

Dither
The method used in digital systems to smooth out the transitions from one bit to another at low levels. Dither makes a digital recording sound and behave more like analog. The better a recording is dithered, the higher its apparent resolution.

DLP
Digital Light Processing. A Texas Instruments process of projecting video images using a light source reflecting off of an array of tens of thousands of microscopic mirrors. Each mirror represents a pixel and reflects light toward the lens for white and away from it for black, modulating in between for various shades of gray. Three-chip versions use separate arrays for the red, green, and blue colors. Single-chip arrays use a color-filter wheel that alternates each filter color in front of the mirror array at appropriate intervals. (See also DMD)

DMD
Digital Micromirror Device. Texas Instruments engine that powers DLP projectors. Uses an array with tens of thousands of microscopic mirrors that reflect a light source toward or away from the lens, creating an image. Each mirror represents a pixel. (See also DLP)

DNR
Dynamic Noise Reduction. A signal-processing circuit that attempts to reduce the level of high-frequency noise. Unlike Dolby NR, DNR doesn't require preprocessing during recording.

Dolby Digital EX Surround
An enhancement to the Dolby Digital 5.1 where a rear center channel has been added creating a 6.1 format. The Dolby Digital Surround EX format does not add an additional discreet recorded channel. The new rear center channel is matrix-encoded in the Dolby Digital left and right surround signals. The recorded Dolby Digital audio consists of five discrete main channels and a sixth, low-frequency-effects (LFE) channel. The two rear surround channels carry the signal for the rear center channel. The Dolby Digital Surround EX format made is debut in the 1999 movie Star Wars Episode I - The Phantom Menace.

Dolby Pro Logic
An earlier form of surround sound. Four separate signals are encoded in a 2-channel recording and re-separated by the processor into left, centre, right and surround channels. The surround channel is usually fed to 2 speakers at the rear. (Dolby and Pro-Logic are registered trademarks of Dolby Laboratories Inc.) (See also Dolby Surround)

Dolby Stereo
Developed by Dolby in the early 70s, Dolby Stereo produces 4 channel sound with three channels of sound in the front (left and right for music and effects and centre for dialogue) and a surround channel for effects and atmospheres.

Dolby Surround
Encodes sound for rear effects channels into the stereo tracks. Needs to be replayed through a decoder to produce surround. (Dolby is a registered trademark of Dolby Laboratories Inc.) (See also Dolby Stereo)

Dome Tweeter
A high frequency speaker with a dome-shaped diaphragm.A high frequency speaker with a dome-shaped diaphragm.

Driver
A speaker without an enclosure; also refers to the active element of a speaker system that creates compressions and rarefactions in the air.

DSD
Direct Stream Digital. A digital encoding format proposed by Sony and Philips used to record SACD albums. DSD samples an audio signal at a fixed rate (frequency) just as in the PCM method. However, instead of recording the volume or amplitude as an absolute number, as in PCM, the DSD method measures and records how much the volume has changed since the last measurement. If the signal is sampled fast enough, the amount of change since the previous sample would be very small. The proposal for DSD is for a sampling rate that's over 2 MHz (2 million times per second). At this high speed the changes in signal strength can be represented with one bit. DSD also compresses the data resulting in a 2:1 reduction. DSD will be able to provide a frequency response from DC to 100 kHz with a dynamic range of 120 dB.

DSP
Digital Signal Processing. DSP can be used to create equalization, compression, etc. of a digital signal.

DTS
Digital Theater Systems. Multi-channel digital surround system that encodes and decodes audio signals enhancing the fidelity of the signal to produce high quality sound. It is used in some movie theatres and is also available in some home theatre digital processors. (See also 5.1 Surround Sound)

DTS ES
An enhanced version of the 5.1 DTS system. Like Dolby's Surround EX, a sixth channel is added. In some cases (DTS ES Discrete), the sixth channel is discrete. Software is backwards-compatible with 5.1 systems, but requires an ES or 6.1 processor to obtain additional benefit. Neo:6 is a subset of DTS ES that creates 6.1 from material with fewer original channels.

DTV
Digital Television. Umbrella term used for the ATSC system that will eventually replace our NTSC system in 2006. HDTV is a subset of the DTV system. While the FCC does not recognize specific scan rates in the adopted DTV system, typically accepted rates include 480i, 480p, 720p, and 1080i.

Dual / Double Voice Coil (DVC)
A voice coil with two windings, generally used in woofers. Each voice coil can be connected to a stereo channel, or both voice coils can be wired in parallel or series to a single channel.

DVD
Officially known as the Digital Video Disc, though marketers unofficially refer to it as the Digital Versatile Disc. DVD uses a 5-inch disc with anywhere from 4.5 Gb (single layer, single-sided) to 17 Gb storage capacity (double-layer, double sided). It uses MPEG2 compression to encode 720:480p resolution, full-motion video and Dolby Digital to encode 5.1 channels of discrete audio. The disc can also contain PCM, DTS, and MPEG audio soundtracks and numerous other features. An audio-only version, DVD-A uses MLP to encode six channels of 24-bit/96-kHz audio.

- DVD-Audio
- DVD-R
- DVD-ROM
- DVD-RW
- DVD-Video
- DVD+RW


DVD Audio (DVD-A)
An audio standard for high quality audio recorded on DVD's that exceed the capacity and quality of CD's. An DVD-Audio disk is capable of recording audio with frequencies up to 96Khz (compared to CD's at 20kHz) and with a dynamic range of up to 144dB (compared to CD's 96dB). DVD-Audio supports multi-channel recordings.

DVI
Digital Visual Interface. Connection standard developed by Intel for connecting computers to digital monitors such as flat panels and DLP projectors. A consumer electronics version, not necessarily compatible with the PC version, is used as a connection standard for HDTV tuners and displays. Transmits an uncompressed digital signal to the display. The latter version uses HDCP copy protection to prevent unauthorized copying. (See also HDMI)

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. In this example the dynamic headroom would equal 3 db.

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.

D\'Appolito
Vertically symmetrical driver array. Typically consists of a tweeter mounted between two woofers. Creates a more-vertically directional sound with evenly spaced lobes in the off-axis response when compared with asymmetrical driver arrays.