1080i A video display standard and HDTV format, where there are 1920 active horizontal pixels and 1080 active scanning lines delivered in
interlaced format.
16:9 The
aspect ratio of a widescreen TV, in which the height of the screen is nine sixteenths of its width. Sometimes expressed as 1.78:1 (~16/9).
16:9 Enhanced A picture format used for widescreen movies on DVD. See anamorphic for a full explanation.
1.85:1 One of the most common
aspect ratios of cinema films, and
consequently of DVDs. This leaves substantial black bands at the top on
bottom of the display on a standard
4:3 TV, but matches quite nicely with the 1.78:1 aspect ratio of a
16:9 widescreen TV. On such a TV, even the expected thin black bands at the top and bottom of the display are often missing, due to the TV's
overscan.
2.35:1 One of the most common
aspect ratios of cinema films, and consequently of DVDs. This leaves very wide black bands at the top on bottom of the display on a standard
4:3 TV, and significant black bands even on the 1.78:1 aspect ratio of a
16:9 widescreen TV.
2.5-way Loudspeakers A
loudspeaker which divides the incoming signal into three different
frequency bands for distribution to
drivers, but in a different way to
three-way speakers. It sends high frequencies to the
tweeter in the usual way, and low frequencies to one or more
woofers. But it sends the
midrange frequencies and the low frequencies to an additional bass/midrange driver in the same way as is done in a
two-way speaker. In other words, all but one of the large drivers handle
bass only, while the last handles both bass and midrange.
3:2 Pulldown The method used in the
NTSC video system for converting the 24
frames per second of film to the 30 frames per second the video system requires.
4:3 The
aspect ratio of a standard TV, in which the height of the screen is three quarters of its width.
480i A video display standard, where there are 480 visible lines delivered in
interlaced format. When delivered in
analog format, it is identical to
NTSC.
480p A video display standard, where there are 480 visible lines delivered in
progressive format.
5.1 The number of channels of audio in a
modern movie. The '5' refers to full range channels: moving clockwise,
left front, centre front, right front, right surround and left
surround. In
Dolby Digital,
DTS and
MPEG 5.1 formats, each of these five channels is capable of a
frequency response covering the full audible range (up to 20,000 Hertz). The '0.1' refers to the
LFE channel, which is not full range but designed to cover up to 120 Hertz, thus the decimal point.
576i A video display standard, where there are 576 visible lines delivered in
interlaced format. When delivered in
analog format, it is identical to
PAL.
576p A video display standard, where there are 576 visible lines delivered in
progressive format.
6.1 An enhancement of the
5.1 channel surround system, versions of this appear in both
Dolby Digital and
DTS. The Dolby Digital version is called
Dolby Digital EX 6.1 while the DTS version appears as either
DTS ES 6.1 Discrete or
DTS ES 6.1 Matrix. The additional channel is intended to sit at the rear of the room (although two
speakers are recommended, even though the
same signal is provided to both). This provides a greater localization
of sounds from the centre rear. This is a very useful enhancement in
cinemas where much of the audience are sitting off-centre, but in
normal rooms with a small number of viewers, it is much less important.
720p A video display standard and HDTV format, where there are 1280 active horizontal pixels and 720 active scanning lines delivered in
progressive format.
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A/D Analog to Digital. See also ADC - Analog to Digital Conversion.
A/V Audio/Visual, as in A/V connections. Most modern TVs have separate sockets for the
composite video signal (that's the yellow one) and sound (black or white, or red and white if stereo).
AAMOF As a Matter of Fact
AC-3 AC-3 is the encoding scheme used in
Dolby Digital, the name by which it is now more commonly known.
AC Alternating Current. An
electric current that reverses direction regularly. More generally, AC
is also used to describe voltage sources in which the polarity of the
signal reverses regularly. Power distribution networks use AC because
it is relatively easy and cheap to alter the voltage (using
transformers)
yielding considerable economies for long distance power transmission.
All the counties in the world use, it seems, either a 50 or 60
Hertz frequency for their power systems. Americas and Japan use 60 Hertz. Europe, Australia and India use 50 Hertz. Compare with
DC.
Academy Aspect Ratio For those with memories. 1.37:1 The
aspect ratio for movies used almost exclusively up to the early 1950s.
Academy Sound Fairly soon after the introduction of talkies in the late 1920s, the movie industry settled on using an
analog optical soundtrack on the edge of the
film to carry the sound. This was read by the projector and converted
to an electrical audio signal. This was a very noisy medium, so in the
absence of advanced noise reduction technology such as
Dolby A (the cinema equivalent of, and precursor to, the Dolby B and C noise reduction systems on
compact cassettes), the situation was eased by sharply cutting the
treble response (at around
5kHz). The bass was also cut, which accounts for the characteristic pinched sound of old movies. The recommended system of
frequency response tailoring was called 'Academy Sound'.
Acoustic Suspension A design for the
enclosure of a
loudspeaker. With acoustic suspension
speakers the enclosure is sealed so that it is air tight, which causes
the air within to become a very active part of the
woofer's suspension. This raises the
resonant frequency of the
driver and lowers its
compliance. Acoustic suspension speakers tend to be less
efficient than
bass reflex designs, and begin fading away their bass at a higher
frequency. But the rate at which the bass
output reduces tends to be less than an equivalent bass reflex speaker,
so they frequently produce greater
bass extension. Also called
infinite baffle.
Active Loudspeaker A
loudspeaker with built-in
amplification for all the drivers. Some speakers have an amplifier built-in for
bass only, but these are not regarded as active. Most loudspeakers are
passive, not active.
Active Subwoofer A
subwoofer with built-in amplification. Most subwoofers are
active, not
passive.
ADC Analog to Digital Converter. A component, circuit or device that converts an
analog signal to a digital one, usually to some form of
PCM. Compare DAC which does the reverse.
Admin Administtrator An Admin is someone who wields a large amount of control over the forums.
AES/EBU Audio Engineering Society/European Broadcasting Union. A
digital audio communication standard most
commonly seen in professional audio applications. Electrically it is
only subtly different to the consumer-oriented
S/PDIF standard, the main variation being a different method of handling the
clocking signal, and it generally being carried by
balanced connections. Nevertheless implementations are seen that seem to be fully compatible with unbalanced S/PDIF.
AFAIK As Far As I Know
AM Amplitude Modulation. A method of impressing a signal onto a
sine wave for its transmission or storage. A constant
frequency sine wave has its
amplitude increased or decreased from moment
to moment to correspond with the signal. The sine wave, called a
carrier, must be of considerably high frequency than any component of
the signal. AM radio is an application of this technique. Very simple
AM receivers (consisting of little other than a crystal and a coil) can
be implemented very easily to receive these signals, although of course
more sophisticated circuits can produce higher quality results.
Amp Short for ampere, or for
amplifier. In the former sense, the amp is a unit of electrical
current. Amps equal volts divided by resistance (or impedance) in ohms.
Amplifier A component or module of a component that increases the
amplitude of an electrical signal. Voltage amplifiers and
current amplifiers are optimised to provide amplification for specific purposes. See also
power amplifiers and preamplifiers.
Amplitude The level of an electrical signal, usually measured in volts.
Analog As in not
digital. An analog signal in an electrical
facsimile of the item being represented. For example, when playing a
stereo DVD, the analog audio outputs of a DVD player trace an
electrical curve that is identical, other than in sheer power, to the
electrical curve that the
amplifier will deliver to the
speakers and this, in turn, is identical to
the pattern of sound waves the speaker will create, except for
distortions that creep into the system. An analog signal can have any
value within set limit, while a digital signal is constrained to a set
of discrete values.
Anamorphic Also known as '16:9 enhanced' or
'widescreen enhanced'. This means stretching a picture out of shape,
making the images tall and skinny. Many widescreen movies have been
filmed on standard
Academy aspect ratio cameras and film stock. This can be done either by wasting a lot of film between each
frame, or making use of the full frame by using an
anamorphic lens to horizontally squeeze the picture together. If a
single frame is looked at, the characters will be as mentioned. When
the film is shown, a reverse form of the anamorphic lens widens the
picture again so that everything appears as it should. On DVDs an
anamorphic widescreen picture is encoded to use all the vertical lines
of
resolution available (576 for
PAL and 480 for
NTSC). When played back on a
widescreen TV it is horizontally stretched
so that the picture contents are shaped normally, but with the benefit
of DVD's full resolution. If played back on a 4:3 TV (that does not
have a widescreen mode), the DVD player's set up menu must be told so
that the DVD player can convert the anamorphic picture to a letterboxed
picture for the TV.
ANSI American National Standards Institutes lumens.
A measure of brightness for projectors under standards set by this
body. This specifies an average brightness produced on a screen of
known reflectivity using a particular test image, or images. A
specification war is underway with each projector claiming a higher and
higher ANSI lumens rating. The amount of brightness required for a good
job from a projector requires three things to be taken into account, in
order of increasing importance: the reflectivity of the projection
surface, the size of the projected image, and the amount of ambient
light in the room. High output projectors (> 1,000 ANSI lumens) are
important for making presentations, class room work and the like. But
for home theater use, look for something lower, preferably under 700.
It will generally give you a longer lamp life and darker black areas,
which are more important for delivering a good quality image. If the
projector has an 'economy mode', try using this. If it doesn't throw
out the color balance too much, it may well deliver a better home
theater image.
Anti-skating A device on a
turntable's tonearm to counteract
skating. This sometimes consists of an adjustable
spring-loaded device near the tonearm's pivot, but is better
implemented as a weight on a string (since the torque applied by this
arrangement remains constant throughout the range of travel).
Aperture Grille A part of a
CRT TV tube. This is a barrier within the tube,
placed between the electron guns at the narrow end and the phosphor
screen at the wide end. It consists of a series of vertical wires or
fine slats. The geometric arrangement permits the electrons emitted for
each color gun to activate only its matching color phosphors. This
alternative to the
shadow mask was developed by Sony and marketed under the name 'Trinitron'.
AR See Aspect Ratio
Artifacts Unwanted visible effects in the picture created by disturbances in the transmission or image processing.
Aspect Ratio The width of the screen as a ratio of its height. A standard TV screen is four units wide to three high, so is described as
4:3 or 1.33:1. A
widescreen TV has an aspect ratio of
16:9 or about 1.78:1. Widescreen cinema movies are typically
1.85:1 or 2.35:1.
ATRAC A system for compressing
digital audio using
perceptual encoding techniques. This was developed by Sony to allow the full contents of a CD to fit onto a
Minidisc, which offers considerably less
storage space. In recent years a new version, called ATRAC3, has been
introduced which permits greater levels of
compression than the original version. This permits ATRAC-based solid state players. The bit rates used by ATRAC3 are 132 and 66
kb/s. The ATRAC compression system also forms the basis of Sony's cinema sound system
SDDS.
ATSC Advanced Television Systems Committee The committee responsible for developing and establishing Digital-HDTV Standards.
Attachment A file that is "attached" to a user's post.
Audiophile A person who places, or would like
to place if circumstances permitted, a high priority on having an audio
system that performs very highly. They have generally trained
themselves to be very discerning about the sound of audio systems. Some
audiophiles stray into a purely
subjective realm.
A-Weighting A system of adjusting
signal to noise ratio measurements to take into account the differing sensitivity of the human ear to different
frequencies. Thus an A-weighted signal to
noise ratio more accurately reflects how a system's noise performance
will be perceived than an unweighted measure.
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B & M Brick and Mortar A retail electronics store/building generally built out of brick and mortar. Generally used to indicate that the store is not an online store or that the store has a physical building in addition to their online store.
Baffle A plate surrounding a
driver in a
loudspeaker. The lower the
frequency of the sound produced by the
vibrating cone of a driver, the more apt it is to simply cause air to
rush from one side of the cone to the other, rather than produce the
compression waves that constitute sound. By adding a baffle around the
driver, this increases the length of the path that air must travel,
lowering the frequency at which this
destructive interference takes place. In most loudspeakers, the
enclosure forms a baffle. In the case of
infinite baffle enclosures, the enclosure is sealed (thus 'infinite') while with
bass reflex speakers a
port is carefully tuned to allow energy from the back of the cone to supplement that from the front at selected bass frequencies. In regular talk, the baffle is the front panel of the loudspeaker.
Balanced An electrical circuit in which both
the signal leads (positive and negative, active and neutral or
whatever) carry equal but inverse signals produced by the source. These
require three conductors: two for the signal plus a separate one for
the
shielding. Balanced connections are fairly
rare in consumer electronics, although they are provided in some
high-end equipment. Well-designed balanced circuits provide excellent
rejection of electrical interference generated in connecting wires.
Balanced connections frequently use
XLR plugs and sockets.
Band-pass Filter An electrical circuit that only permits signals between two particular
frequencies to pass through. An example is section of a
crossover network that allows only the middle frequencies to be delivered to the
midrange driver.
Compare
low pass filter and
high pass filter.
Bandwidth Either the range of
frequencies which a component can deal with competently (often specified as the range across which the attenuation is no more than
3dB), or the frequency range required to carry a signal. For example, the bandwidth required for a
composite video signal is somewhat more than
5MHz.
Bass Low
frequency sounds, typically below around 150
Hertz, although the dividing line between bass and midrange is one of opinion. The human ear is less sensitive to bass than to midrange.
Bass Extension An imprecise term concerning how low in
frequency a loudspeaker or
subwoofer can still operate to produce usable output. A typical bookshelf-sized speaker may manage a bass extension of 80
Hertz (say, at -10dB), a good
floorstanding speaker may manage 30 or 40 Hertz, an inexpensive
subwoofer 40 Hertz, a middling one 25 to 30 Hertz, an expensive one 16
Hertz.
Bass Management A facility in
home theater receivers that permits some of the speakers in a
5.1 channel system to be specified as 'small' rather
than 'large'. 'Large' speakers receive the entire signal for their
respective channel, but 'small' speakers have the
bass stripped off and sent elsewhere. If a subwoofer
is attached, this bass goes to it, otherwise it goes to the front main
speakers (you will notice that most systems will not permit you to
select 'small' for the front stereo pair if you have the subwoofer set
to 'off'). Some home theater receivers permit you to choose the
crossover frequency for bass management, but many use a standard value of 80
Hertz.
Bass Reflex A design for the
enclosure of a
loudspeaker. With bass reflex speakers the enclosure has a
port that permits air to flow between the interior
and exterior of the cabinet. The port is a hole, usually backed by a
tube. The dimensions of the port are carefully calculated so that it
permits
bass at a selected
frequency to be produced from the interior of the enclosure (driven by the back of the
woofer's cone). This arrangement permits a bass reflex speaker to generally achieve greater efficiency than an
acoustic suspension speaker, and it
extends the depth at which bass may be produced without significant
attenuation. However for frequencies below the band produced by the
port, the output drops off quite rapidly.
BB Bulletin Board Generally refers to an online forum board.
BEV Bell Express Vu A canadian DBS provider that provides programming using standard 18" DBS satellite dishes.
Beta Or Betamax. The first widely-used consumer-level
video recording system on the market. Developed by Sony in the late 1970s, it eventually lost out to the rival
VHS system, which came to market about a year later, primarily because of shorter playing and recording times.
BFD Behringer Feedback Destroyer Pro audio unit that is used as a parametric equalizer to level the response of subwoofers.
Bipole A
loudspeaker designed to offer well-dispersed sound by firing its high
frequencies, and in some models its full frequency range, in two opposing directions. Unlike
dipole speakers, the sound is in
phase from all the drivers.
Bit The smallest unit of digital information. A single bit can carry just one of two values: 0 or 1. There are eight bits in a
byte, 1,024 bytes in a
kilobyte, 1,024 kilobytes in a
megabyte and 1,024 megabytes in a gigabyte.
Sometimes, though, the traditional 1,000 is used rather than 1,024,
leading to confusion. A bit should generally be abbreviated as
lower-case 'b' (compared to 'B' for byte). Thus 128kb/s means 128
kilobits per second, whereas 128kB means 128 kilobytes.
Bit Depth The size of the number that records each
digital sample.
Since the system is digital, the number relates to powers of two. The
compact disc uses a bit depth of 16, which allows 65,536 different
levels to be used to track the
analog source signal. DVDs usually also use
16, but may also use 20 bits (which gives over a million levels) or 24
bits (which gives more than 16.7 million levels). The greater the bit
depth, the lower the
harmonic distortion and quantization noise, and the more storage space required for the signal.
Bit Rate The number of digital bits a system
transfers per second. In general, the higher the bit rate, the higher
the quality of the signal. In every case, the higher the bit rate, the
more data space required. With audio bit rates are measured in the
hundreds of kilobits per second
(kb/s). With DVD video, they are measured in megabits per second
(mb/s).
Bitstream The digital audio output of a DVD
player, when switched to outputting the DVD's native digital audio
format. Most DVD players can be switched to output a
Dolby Digital bitstream, or convert the digital output to
PCM.
Blu-ray A high capacity development of the DVD which uses higher
frequency (blue) rather than red light
frequencies for reading the disc. The combination of shorter
wavelengths and other enhancements bumps up the maximum capacity from
8.5GB for a dual layer DVD to around 27GB, allowing the storage of high definition video.
Bob One of several strategies used in deinterlacing video. Bobbing is where each field is displayed all by itself
in sequence. The intermediate lines are created by interpolating from
the lines above and below it. This has the effect of reducing the
vertical resolution at any instant of time by half (but it doesn't seem
as bad as this, thanks to the interpolation), but smoothing pans
because the two fields are displayed one fiftieth of a second apart.
This is useful for video sourced material, in which the two interlaced
fields constituting the full video
frame were actually captured at slightly different times from each other, causing a combed effect on vertical lines. Compare
weave.
Byte Eight
bits. A byte can represent numbers between 0 and 255, or when interpreted as signed integers, between -128 and +127.
BTW By The Way
BUD Big Ugly Dish Large ugly C-Band dish usually from 5' to 10' in diameter.
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Cantilever The thin rod within a turntable's cartridge that transmits the movement of the
stylus in response to a record's groove to the interior components of the cartridge that generate the electrical signal.
Carrier A
sine wave which may be modulated by a signal to form an
AM signal. The frequency of
the carrier must be significantly higher than that of the modulating
signal. In practice, the carrier is usually a radio frequency sine
wave, and so is two orders of magnitude higher in frequency than the
signal.
Cartridge The device that converts the movements of a
stylus in the grooves of an
LP to electrical signals. The cartridge is a small, light-weight device, secured to the end of a
turntable's tonearm by
means of two screws mounted 12.5mm apart. The movements of the stylus
are transmitted through a cantilever to some form of electrical
generating device. The two main types of cartridge are
ceramic and magnetic. The latter is further subdivided into moving magnet and moving coil types.
CAV Constant Angular Velocity As opposed to
CLV. A method of spinning a disc or disk carrying a
signal. CAV means that the rate of spin remains unchanged regardless of
where the reading device is on the surface. An
LP is an example (which is part of the reason why the outer tracks tend to sound better than the inner ones). While
CDs are designed to be operated at a CLV, fast CD-ROM drives actually run them with a CAV.
CEDIA Custom Electronic Design & Installation Association CEDIA is an international trade association of companies that specialize in designing and installing electronic systems for the home.
CBR Constant bit rate – as opposed to
variable bit rate. The signal (video or audio) is
digitally encoded so that a fixed amount of data flows each second.
This has the advantage of making the space requirements for the signal
easy to calculate.
DTS and
Dolby Digital are both CBR systems, as are the earlier versions of
MPEG audio and video
compression. Most
MP3 files are CBR encoded, although the format does support VBR as well.
CD Compact Disc -- This is the familiar 120mm optical disc. It carries a digital
PCM representation of a two channel analog signal, along with error correction information. The analog signal is
sampled at 44,100 Hertz and uses a
bit depth of 16.
CD Emphasis When the
compact disc was first developed, the designers
implemented a rather surprising element in its specification. This was
a pre-emphasis, de-emphasis cycle. In brief, this permits the
treble in the source signal to be boosted before the CD is mastered (pre-emphasis), recording this fact by a special
bit in the package around each segment of audio
data, and cut again by the CD player (de-emphasis). When cut, it also
had the advantage of reducing any noise due to the recording medium.
But, in practice, there is no such noise, so initially it can be hard
to see the purpose of this. Then when you consider that for most music
the amplitude of the signal reduces as the
frequency increases at around
6dB
per octave, you can see that the amplitude of the higher frequency
components would be very low and, consequently, subject to increased
quantization noise. Boosting the higher frequencies significantly reduces this noise accordingly. The
frequency response of the signal is
pre-emphasised by boosting the signal from 50µs (microseconds -- which
is what engineers used to specify frequency in some contexts) or 3,183
Hertz, and levels out at 15µs, or 10,610 Hertz, with a maximum boost of 10.45dB. CDs that actually use this are rather rare.
Ceramic Cartridge A cartridge
that produces an electrical signal through a piezoelectric effect. Such
cartridges are rarely used in high fidelity applications because they
require a relatively high tracking weight (usually upwards of 10
grams), have a low
compliance and produce an uneven frequency response. However they do have the advantage of producing a rather higher output voltage than
magnetic cartridges, and their frequency response characteristics approximate the
RIAA equalization curve, allowing simpler circuitry to be used with the signal.
Chapter The divisions within a
Title on a
DVD Video. Navigation is most easily achieved by using the forward and reverse 'skip' keys of the DVD player's remote control.
Chroma The color component of a TV picture
signal. This comprises of two color difference signals (the CR and CB)
matrixed together. While these two signals are carried separately on a
DVD, if the signal is delivered to the TV via an
S-Video cable, they are matrixed together, slighty reducing color clarity.
Cinch Plug Another name, used by companies that presumably don't like to use the opposition's brand name in their own literature, for
RCA plug.
Class A A power amplifier in which a sufficient
DC bias voltage is applied to the
power transistors so that the output signal always operates entirely in
the positive or negative part of the cycle, entirely avoiding
crossover distortion. This makes
them quite wasteful of power since even at idle a considerable voltage
is being generated. The DC bias is filtered out before being fed to the
speakers.
Class A/B A power amplifier in which a certain amount of
DC bias voltage is applied to the
power transistors so that, at low power outputs, the output signal
operates entirely in the positive or negative part of the cycle,
avoiding
crossover distortion. Thus, at low outputs, a Class A/B amplifier operates in
Class A mode. At higher outputs the signal does
cross over the zero point, effectively entering Class B territory. This
design is a compromise between the efficiency of Class B amplifiers (in
which there is no DC bias) and the elimination of crossover distortion
in Class A designs. The DC bias is filtered out before being fed to the
speakers.
Cliff Effect Where the degradation of a signal's
reception does not gradually increase with a reduction in signal
quality or strength, but maintains full quality until some threshold,
at which point the signal collapses into incoherence.
analog transmissions tend to degrade gradually.
Digital transmissions in modern systems (with
error correction built in) tend to maintain full quality, but then cut out completely at the threshold.
Clipping
When the
amplitude of a signal reaches some limit
determined by the equipment in use, it hits a ceiling (and floor)
beyond which it cannot proceed. So the top and bottom of the wave is
simply lopped off. The more it attempts to exceed the limit, the more
that's chopped off, and the closer to a
square wave the formerly rounded wave begins to look. This causes it to generate lots of harmonics,
and so it sounds very distorted. The graphic to the right shows a sine
wave at the left, and then the same sine wave amplified by just three
decibels, to the right. This relatively minor clipping generates a
third harmonic of 14%, a fifth harmonic of 3%, a seventh of 1.8% and so
on. Truly awful sounding. Clipping is often caused by turning up an
amplifier too loud so that its power limits are exceeded.
Clocking Signal A signal used to synchronise items of equipment which are communicating
digital audio or video signals to each
other. The lack of a suitable clocking signal would allow their timing
to drift apart from each other since their internal clocking signals
would generally not be identical, so digital
samples would be lost.
Cloth Ears A purported characteristic of a
person, the possession of which is alleged to account for his or her
inability to notice differences in the sound quality produced by
different pieces of equipment. Those so accused, assuming they have
taken care to listen carefully to the demonstration, should
forthrightly reject the allegation.
CLV Constant Linear Velocity As opposed to
CAV. A method of spinning a disc or disk carrying a
signal. CLV means that the rate of spin varies in order to maintain a
constant velocity of the track at the point where the reading device is
on the surface. A
CD playing back in an audio CD player is an example
of this, because the CD player runs at about 500rpm at the start of the
CD (where the inner grooves are being read), gradually reducing speed
to about 200rpm as the track nears the outer edge.
Coaxial Digital The digital audio output signal of a DVD player in an electrical format, rather than
optical. The data format accords with the
S/PDIF specification.
Codec Compression/Decompression.
A system which compresses a signal in some way for storage or
transportation and then decompresses it at the point of delivery.
Examples are
MPEG,
Dolby Digital and
DTS. These systems use a codec to reduce the amount of data in the signal. Other forms of codec, particularly in the days of
analog audio systems, compressed and then decompressed the
dynamic range of the signal, not to reduce the size of the signal but to reduce noise levels. One consumer system was called 'dbx'.
Coloration An unwanted alteration in the
character of audio. Significant coloration of sound can make
instruments and voices sound unrealistic. It may be caused by
harmonic distortion, vibrations of component parts (for example, the panels of
an inadequately braced
loudspeaker enclosure) or, most commonly, through an uneven
frequency response.
Color Difference These are two of the three
components of a color video signal. One is the Red color difference
signal, called variously Y-R or CR while the other is the Blue color
difference signal (Y-B or CB). They are created from the original
RGB signal by creating a
luminance signal (Y) and then subtracting this
from the red and blue respectively (thus the name, color
'difference'). When combined with the luminance signal the original
three RGB signals can be recreated with very little degradation. The
two color difference signals and the luminance signal are, together,
known as
component video.
Compact Cassette A neatly packaged magnetic tape
recording and playback system for audio introduced in the 1960s. This
uses a narrow plastic tape with four tracks running at a speed of
28.6mm/s (1 1/8 inches per second), contained in a sturdy plastic
enclosure. In consumer equipment, only two of the tracks are accessible
at any one time, providing
stereo recording and playback. The tape is
turned over (or an auto-reverse transport moves the recording and
playback heads sideways) to access the other two tracks. Some
semi-professional four track recording systems allow all four tracks to
be recorded and played back at once, or even separately to permit
multi-track recording. All cassette decks capable of recording (some
are playback-only) have at least two heads: a record/playback head and
an erase head. Some better decks include three heads, with separate
record and playback heads to allow close-to real-time monitoring of the
recorded material directly from the tape, and allowing the heads to be
optimised for their different functions. While initially very low in
fidelity, in the early 1970s tremendous advances were made in tape
formulations, first with Chromium Dioxide magnetic materials and then
later with 'Metal' tapes, which extended the high
frequency response and improved their saturation characteristics. The addition of
Dolby B noise reduction (and later Dolby C) reduced the inherent problem of high noise levels due to the low tape speed.
Compander Compressor/Expander. A noise-reduction system that works by compressing the
dynamic range of the audio before
recording, and expanding it again by an equivalent amount during
playback. An example of this was the dbx system.
Compliance The degree of 'springiness' in a mechanical system. For example, the cone of a
loudspeaker driver with a soft suspension which can move to and fro relatively easily is more compliant than one with a stiff suspension. The
stylus of turntable cartridge with a high compliance tends to follow the
excursions of the groove more easily than a that of a cartridge with low compliance.
Component Video Three components of a video signal that, together, constitute the full signal. The three components are
luminance (Y), red
color difference (CR) and blue color difference (CB). These can be wrapped into each other to various degrees to form
S-Video signals or composite video
signals. On DVD the video signal is carried in component video form.
The best way to deliver the DVD's picture to the TV is therefore via
either component video connections (in which case, the TV reconstitutes
the original RGB signal required for its
CRT), or RGB (in this case, the
DVD reconstitutes the RGB signal).
Composite Video This is the way that the three
component video signals are wrapped
together to form a single signal, suitable for TV broadcast or carrying
on a single two-conductor cable. The two
color difference signals are first matrixed together to form the
chroma signal, and then the
luminance signal is matrixed into this to
create a single composite video signal. This process results in some
cross interference between the chroma and luminance portions of the
signal, reducing picture quality.
Compression Reduction. Air is compressed by squeezing it into a smaller space.
Digital signals are compression by reducing the
amount of data space required to hold them. Some digital data
compresses readily, due to easily identifiable redundancy within the
data. So, for example, a text document typically has a lot of space
characters and 'e' characters, so other ways of expressing these can be
found.
Digital audio and video signal tend not to
carry a lot of redundancy, so systems that compress these highly rely
on eliminating some of the data and are consequently called
lossy compression systems.
Compression Driver A kind of
loudspeaker driver.
Rather than using a speaker cone to directly vibrate the air in a room,
a compression driver has a throat in front of the moving part that
causes a relatively small amount of air to compress and rarify rapidly
in response to the movement of that part. This, in turn, drives the
vibration of the air in front of it into the room, through some form of
horn. Most compression drivers use
piezo effects for the initial vibration,
although some use more or less conventional cones. Compression drivers
offer significantly higher
efficiency than conventional drivers, allowing high output levels for a given input power, but can tend to reduce the
dynamic range of the input signal and
color the sound.
Compression Ratio The extent to which a signal (particularly digital signals) is compressed, expressed as a ratio of the uncompressed size to the compressed size of the data.
MP3, for example, with a bit rate of 128kb/s has a compression ratio of about 11:1.
Contrast Ratio The ratio between the darkest blacks (ie. the
pixels in the area are fully shut off) and the
brightest whites (pixels fully on) capable of being produced on-screen
by a projector or other display device. For quality home entertainment
work, this is a far more important than the
ANSI lumens rating. LCD projectors typically have a specified contrast ratio of between 500:1 and 1,100:1.
DLP projectors tend to start around 1,000:1 and the newer models can reach as high as 3,500:1.
CRT projectors, noted for being the best at producing black blacks, are up around 15,000:1.
Constructive Interference Where two signals, added together, act in sympathy with each other to boost the signal level. For example,
bass from a subwoofer may, at certain
frequencies, bounce from a nearby wall and
that reflected signal may interfere with bass still coming directly
from the subwoofer to effectively increase the output at that
frequency. But it is also likely, at other frequencies, to result in
destructive interference.
Crossover Distortion A small discontinuity (or, at least, nonlinearity) in a signal when a transistor-based
amplifier circuit switches from positive to negative operation. This is addressed by
Class A and Class A/B designs. Sometimes called 'zero cross distortion'.
Crossover Frequency The
frequency at which a signal is handed from one component to another. This applies in
crossover networks and
bass management systems.
Crossover Network The set of components in a
loudspeaker that divides up the incoming signal, sending the
bass to the
woofer, the treble to the
tweeter and, sometimes, the middle
frequencies to a
midrange driver. The crossover network
uses resisters, capacitors and inductors (coils) to divide up the
signal. Some high end systems use active crossover networks. In such
cases, the division is made before the signal is amplified, so a separate
amplifier is required for each driver.
Crosstalk Where a signal (particularly audio)
leaks from one channel to another. Thus a voice may be intended to be
entirely in the left channel of a
stereo recording, but some portion of it appears
in the right, dragging the apparent position of the voice somewhat
towards the centre of the
sound stage. Normally specified by the inverse of crosstalk:
separation.
CRT Cathode Ray Tube A vacuum tube in which a hot cathode emits a beam of electrons that pass through a high voltage anode and are focused or deflected before hitting a phosphorescent screen. The original screens/displays used for computer monitors and televisions consistig of a red, green, and blue color lense. The appropriate signals are matched to the
appropriate red, green and blue phosphors by means of either a
shadow mask or an aperture grille.
Current The quantity of electrical charge moving through a circuit over a given time. The unit for current is
amps or amperes.
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D* DirecTV Satellite TV service in the U.S.
D/A Digital to Analog See also DAC
D-ILA Direct Drive Digital Image Light Amplifier
-- A projection technology used by JVC. It uses three reflective Liquid
Crystal on Silicon panels which control light representing the signals
for the three different colors.
D-Terminal A video connection that delivers
component video, along with useful ancilliary data. Despite the 'D',
don't confuse it with any digital video standards such as
DVI. The video signals are the same as component
video (with up to 1080i high definition supported), while additional
signals indicate the resolution of the video signal, whether it is
progressive or interlaced, and its
aspect ratio. The display device can use this information to set itself appropriately.
DAC Digital to Analog Converter. A component, circuit or device that converts
a digital signal to
an analog signal. Compare ADC which does the reverse.
Damping Factor A specification for
power amplifiers which suggests the degree of control that the amplifier exercises over a connected
loudspeaker. It is the ratio of the
nominal impedance of the speaker (and is typically quoted for eight
ohms) to the internal
impedance of the output stage of the amplifier. A high internal impedance for the amplifier means that its
frequency response will vary with real-world speakers since their impedance varies across their
frequency range. It also means that the
driver, which wants to do its own thing under the
influence of air, its suspension and so forth, rather than what the
signal is telling it to do, will face a relatively high impedance to
the voltage it is generating back into the amplifier. Consequently it
will be freer to do its own thing, rather than what the amplifier is
telling it to do. However the damping factor quoted for amplifiers does
not take into account the impedance of the wiring between amplifier and
loudspeakers, nor the impedance of the speakers' own
voice coils. Consequently there is only a modest performance gain between a damping factor of, say, 60 and one of 600.
DAT Digital Audio Tape. A compact tape developed in the late 1980s by Sony which stores audio in
PCM format. The tapes look very similar to the
MiniDV tapes used in digital video cameras, but are somewhat larger,
measuring 71mm wide by 53mm deep and 10mm thick. The reading part of
the tape is protected by the casing. In order to pack sufficient
capacity on, the tape is read using a helical scan head in the same way
as a
VCR. The default format for DAT is a 48
kHz sampling frequency and 16
bits of
resolution, but they can also be switched to 44.1kHz.
dB See Decibel.
dBFS Decibel - Full Scale. The level of a signal, measured in
decibels, with reference to the maximum possible level of the signal. With
digital audio the maximum recording level is 0dBFS, so all measurements of the signal are negative values.
DBS Direct Broadcast Satellite or Digital Broadcast Satellite
dBSPL Decibel - Sound Pressure Level. A measure of sound intensity. This is a logarithmic measure. To increase the sound level by three
decibels, it is necessary to double the power output.
A 10dB increase in sound level roughly equates with a perceived
doubling of volume level. A figure of around 120-130dB is normally
considered to be the threshold of pain. dB is sometimes loosely used as
a synonym.
DC Direct Current. An electric
current that retains its level and direction, at least in the short
term. More generally, DC is also used to describe voltage sources that
deliver this kind of current. DC is generally used at low voltages
within electronic equipment. Batteries deliver DC. Compare with
AC.
DCC Digital Compact Cassette. An attempted replacement for the
compact cassette introduced by Philips in the late 1980s, early 1990s. This recorded audio in
digital format, but used a
lossy compression system. It failed to make headway since Sony's
Minidisc had the advantage of direct access
and, more recently, the recordable CD provides convenient and cheap
recording with higher quality.
DD See Dolby Digtial
Deinterlace The conversion of an interlaced video signal to a progressive video signal. Two common systems are
weaving and bobbing.
Decibel Abbreviation dB. A logarithmic measure of ratio. To determine the decibel relationship of, for example, two
voltages you use the formula dB=20*log(V1/V2). If
the result is negative, V1 is less than V2. If positive, then V1 is
greater than V2. For power the formula is dB=10*log(P1/P2). dB is often
used loosely as shorthand for
dBSPL.
Destructive Interference Where two signals, added together, act in opposition to each other and reduce the signal level. For example,
bass from a subwoofer may, at certain
frequencies, bounce from a nearby wall and that reflected signal may, if arriving back out of
phase, interfere with bass still coming directly
from the subwoofer to effectively reduce the output at that frequency.
But it is also likely, at other frequencies, to result in
constructive interference.
Dialog Normalization Frequently called 'dialnorm'. A
metadata indication in a
Dolby Digital bitstream of the volume level of the dialog in
an audio signal. Dolby Digital decoders can use this 'flag' to adjust
the volume level of the whole audio stream, so that the dialog levels
of different program sources remain the same. Most DVD movies have this
flag set to '27', which means
-27dBFS. If the decoder is set to act upon this, it will reduce the level of the signal by
4dB
because it means that the dialog is set 4dB higher than the calibration
level of -31dBFS. It is important to note that this volume adjustment
is made not just to the dialog, but to the entire sound track. It is
also important to note that it does nothing to the sound other than
adjust the overall volume level. Whether or not the dialog
normalization feature actually works as hoped -- in the sense of
bringing the voice levels of all programs into line with each other --
depends entirely on the engineers who mix the sound setting the dialog
to the appropriate level in the first place. Dolby Digital encoders
typically default to the value of 27, and must be explicitly changed
for a different value. Many home theater receivers report dialog
normalization with reference not to 0dBFS, but to -31dBFS (the
calibration level), and so a level of -27dBFS is reported as -4dB.
Digital As opposed to
analog. It is a method of representing
real-life signals (which are generally effectively infinitely variable)
by using discrete numbers, usually binary numbers (a pattern of 1s and
0s). Holding discrete values, rather than the infinite number of
intermediate levels used by analog, makes digital signals relatively
resistant to distortion and noise. The reason is that if any inaccuracy
creeps in, unless very severe it will not affect the signal enough to
throw it off. Consider a binary system. If all data is represented as
either 0 volts or 1 volt, then it doesn't matter if some interference
causes the 1 volt level to be sometimes 1.1 volts, sometimes 0.9 volts.
The receiving module will regard any voltage as greater than 0.5 volts
as 1 volt and treat it accordingly.
Digital Audio Any one of a number of systems for recording sound using a
digital representation of the sound. Some digital audio systems are straightforward representations of the
analog signal. Examples of these are
PCM, DSD and MLP. Other systems take a simple digital signal (usually PCM) and process it heavily to reduce its size. Examples are
Dolby Digital, MPEG audio and DTS.
Digital Compression Reduction of the size of digital data files.
DIN Deutsche Institut fuer Normung.
A German standards body. DIN frequently appears in specifications to
give an indication of how measurements were conducted, and also applies
to a number of connectors approved by the body.
Dipole A
loudspeaker designed to offer a diffuse, non-directional sound by firing its high
frequencies in two directions, out of phase
with each other, so that a listener receives few aural clues as to
their exact location. To make such speakers work optimally, they should
be placed so that the axis running through the front and rear
tweeters is at 90 degrees to a line drawn from the speaker to listener. This will maximise the cancellation (see destructive interference) of direct radiation from the speaker to the listener's position.
Direct View A display device in which you look directly at the component which produces the picture. Thus a standard
CRT TV is a direct view device, as is a
plasma or LCD display. An RPTV and a front projection system are not direct view since you are looking at an image projected onto a screen.
Direct Sound Field A speaker system in which the great majority of the sound that you hear is coming directly from the
loudspeakers, and very little from
reflections from surfaces within the listening space. Direct sound
field speakers tend to deliver a more accurate reflection of the
source, and sharper stereo
imaging, than
reverberant sound field speakers. Direct sound field sound can be achieved by choosing speakers with restricted
dispersion and placing them close to you.
Dispersion The degree to which
loudspeakers spread their sound production in all directions, rather than directly to their front. All loudspeakers widely disperse their
bass. But as the
wavelength of a sound nears the size of a
driver's cone diameter, the sound tends to become more directional.
Distortion An inaccuracy in the reproduction of a signal. In the case of audio, it is normally regarded as being composed of
harmonic distortion and
intermodulation distortion. But used more broadly, it can also encompass
frequency response variations and noise. In the case of
lossy compression technologies, some distortion consists of spurious noise
(not harmonically
related) surrounding the signal. When 'distortion' is quoted as a
specification without qualification, it normally refers only to
harmonic distortion.
Dither Very low level noise, usually
'white' in character, added to a digital audio signal to reduce
harmonic distortion. It typically is just a random variation in the
least significant bit of the digital signal. In some systems, such as Sony's
SBM, the noise is shaped to yield a lower noise floor in the more easily audible
midrange and low treble, by pushing much of the noise into the
near-ultrasonic.
DLP Digital Light Processor A type of projector based on the
DMD. Most DLP projectors use a single DMD, so to
derive the three necessary colors they have a spinning wheel with
color filter windows, carefully synchronised with the signal driving
the DMD. High end DLP projectors use three DMD panels, avoiding the
need for the spinning wheels. This is likely to remove the
Rainbow Effect that afflicts many DLP projectors. The main advantages of DLP projectors over
LCD-based ones is that the narrower band of electronics around each active
pixel on the DMD's surface reduces the
screen door effect, and they produce
significantly darker blacks (or, more correctly, they are better at
stopping light from coming out the lens when a pixel is supposed to be
black).
DMA Designated Market Area Determines what local channels you can subscribe to.
DMD Digital Micromirror Device -- a technology available (until the patents run out, it seems) only from Texas Instruments. This is used in
DLP projectors and controls the transmission of
light by means of hundreds of thousands of microscopic mirrors on its
surface which physically swing through ten or twelve degrees in
accordance with the signal. They come in a range of
resolutions, from
SVGA (800 by 600) through
XGA (1,024 by 768) in the
4:3 aspect ratio, and 1,024 by 576 (woo hoo! A real
PAL-optimised one!) to 1,280 by 720 in the latest Mustang HD2 DMD.
DNR See Dolby Noise Reduction
Dolby Digital Dolby Digital is an encoding scheme invented by Dolby Laboratories as a way of
compressing digital audio so that it uses a lot less
data space. It is also known as AC-3. Originally developed as an audio
compression system for US digital television, it achieved prominence by
allowing multiple channel sound tracks to fit onto standard 35mm cinema
film prints (in between the sprocket holes on the film!), it has become
the de facto standard for DVD. The compression system uses
perceptual encoding, similar to
DTS, MPEG audio (including
MP3) and Sony's
SDDS and
ATRAC. It can carry up to
5.1 channels of sound, but does not necessarily have that many. Dolby Digital 2.0 (that is, stereo) can be encoded with
Dolby Pro Logic surround sound. The Dolby
Digital bitstream can also carry codes (metadata) to control playback
parameters in the Dolby Digital decoder. Dolby Digital apparently
supports bit rates of up to 640kb/s, but on 5.1 (or higher) channel
DVDs the bit rates actually used at 384kb/s and 448kb/s. (Note, the 'k'
here stands for 1,000, not 1,024). Dolby Digital bitstreams also
include
metadata for controlling the operation of the decoder.
Dolby Digital EX 6.1 A new surround sound standard which provides the usual 5.1 channels plus an additional channel: the centre rear channel. Unlike
DTS ES 6.1 Discrete the additional
channel is not carried discretely but is encoded into the two rear
channels in a similar way to the front centre channel is encoded into a
Dolby Pro Logic sound track. Movies
prepared for Dolby EX 6.1 presentation in cinemas should have the same
encoding on DVD. However EX 6.1 is compatible with 5.1 channel systems
in the same way that Dolby Pro Logic is compatible with stereo systems.
More correctly, this should be termed LucasFilm
THX 6.1 since it was developed by them, but the name above seems to have come into common currency.
Dolby HX |
