"D" Terms
DA(Digital to Analog) Processing of digital audio or video signals analog which should be the final stage of processing before being presented through playback.
DAC
(Digital to Analog Converter) A type of processor found in Home Theater equipment the converts digital audio signals such as those read off a CD or DVD to analog that we can hear. Receivers and DVD players might have DACs. These chips are an important part of the signal path of your Home Theater equipment, there is a wide variety in quality of DACs. Burr-Brown and Wolfson are high quality name brand DACs.
DAT
(Digital Audio Tape) A cassette tape recorder that records digital rather than analog signals magnetically like a conventional tape deck. The technology predates CD-RW but effectively performs the same function. Although the technology has fallen from consumer favor it's far from obsolete because it's a digital recording technology. As long as you can get blank tapes a DAT in your system will always have a purpose.
Datastream
See Bitsream.
Db
See Decibel.
DC
(Direct Current) Electrical energy that flows in one direction.
Decibel
(dB) One tenth of a Bel. Named for Alexander Graham Bell. A unit of sound pressure or loudness as perceived by the human ear. 1 dB is considered the smallest difference between two volume levels the human ear can hear.
Definition
In both audio and video the amount of definition is the amount of information being displayed at once. High definition images can be measured in resolution either as pixels or scan lines, differences are obvious to the viewer. In sound definition is generally measured by Pulse Code Modulation (PCM), number of bits per cycle and number of cycles per second. In sound the definition will determine how many different sounds can be heard at the same time. Audio definition is less obvious than video, so technology that delivers higher definition sound are slower to catch on than higher resolution video.
Delay
The time between a sounds production and delivery to the listener. Sound always travels at a static rate, the delay between sound coming from speakers in a Home Theater system and that sounds arrival to the ear is instrumental in the audience's perception.
Digital
Information expressed in binary. Binary information, thanks to semiconductor technology, is easily transmitted and processed electronically without degradation of the input value. Since we see and hear in analog, the science behind Home Theater technologies is a perpetual dance between digital convenience and analog purity and realism.
Digital Output
A digital output is generally found on a CD or DVD player and usually audio (S/PDIF is a digital audio output format) but today there are video outputs too. Conventional wisdom states using digital outputs when available is superior because it retains the purity of the signal read from the media. Generally you only want digital to audio conversion to take place as close in the signal path to the point the information reaches your eyes and ears (IE before being amplified or displayed on the TV). This is why digital video outputs have been a breakthrough for Home Theater.
Digital Video Recorder
(DVR) See: Personal video Recorder (PVR) or (See PVR on Home Theater Focus).
