back-emf (back-electromotive force)
Literally, back-voltage, is a phenomena found in all moving-coil
electromagnetic systems, but for audio is most often used with respect
to loudspeaker operation. This term describes the action where,
after the signal stops, the speaker cone continues moving, causing
the voice coil to move through the magnetic field (now acting like
a electrical generator or dynamic microphone), creating a
new voltage that tries to drive the cable back to the power
amplifier's output. If the loudspeaker is allowed to do this, the
cone flops around like a dying fish. It does not sound good!
The only way to stop back-emf is to make the loudspeaker "see"
a almost dead short, i.e., zero ohms looking backward, or as close
to it as possible. See:
background music Music played
at a lower volume used as an alternative to silence in public and
commercial spaces. Intelligibility is now an issue as this music
is not intended to compete with human speech. Often background
music is preformed without lyrics and not by the original artist.
Contrast with foreground music.
balance control A control found most
commonly on professional and consumer stereo preamplifiers, used
to change the relative loudness (power) between the left and right
channels. One channel is made (apparently) louder by attenuating
the opposite channel. Although many circuits are used by different
manufactures the ideal balance control should attenuated both channels
by 3 to 6 dBs at the center position. Rotating it away from
the center position causes one channel to be attenuated, while having
no effect on the other channel, and vice-versa. At each extreme
of rotation one channel is shorted to ground and therefore completely
off while the other channel is unattenuated. Contrast with
balanced line The preferred
method (for hum free) interconnecting of sound systems using a shielded
twisted-pair cable. Because of
its superior noise immunity, balanced lines also find use in interconnecting
data signals, e.g., RS-422, and digital
audio, e.g., AES/EBU. The principal
behind balanced lines is that the signal is transmitted over a complete
path down one wire and back on the another ( think of a close line
around two pullies ). The shield does not carry any information,
thus it is free to function as a true shield, but must be earth
grounded at one end to be successful.
[Long Answer: To understand why balanced lines are so successful,
first examine a balanced, or differential (equivalent term) output
stage, and then an input stage: A differential output stage simultaneously
drives two lines, one positive and one negative. The voltage difference
between these two wires is the audio signal. Note that the
audio signal exists uniquely between these two lines not
between them and ground. The complete circuit path travels down
on the positive line and back on the negative line. Ground is not
needed to transmit the signal this is the essence and power
of balanced lines. Ground is used only for shielding and safety
purposes. Conversely, an unbalanced line is one that transmits
the audio signal between one wire and ground. The circuit path is
down the wire and back through the shield cable connected to ground.
Ground is the return path; the circuit does not work without it.
A balanced (or differential) input stage extracts the difference
between the two input lines, and that, of course, is the desired
audio signal. It receives the difference signal sent down the cable
by the differential output. This circuits primary advantage
is its great noise rejection ability. It has what is called common-mode
rejection. The concept here relies on induced (received form radiated
signals) noise showing up equally (or common) on each wire. It is
mainly due to EMI (electromagnetic interference: from near by magnetic
fields), RFI (radio frequency interference: from strong broadcast
radio signals), electrical noise present in the ground references,
or a combination of all three. Balanced line designs have equal
impedance from each line relative to ground, guaranteeing equal
noise susceptibility. Since the balanced input stage amplifies only
the difference between the lines, it rejects everything else (noise)
that is common ( or equal ) in both lines.]
bandpass filter A filter
that has a limited passband between two frequencies. Neither
of the cutoff frequencies being zero or infinite. The bandpass frequencies
are normally defined as the frequencies that are attenuated
-3 dB from the passband.
band In telecommunication, a band -
sometimes called a frequency band - is a specific range of frequencies in the radio
spectrum. Each band has a defined upper and lower frequency
bandwidth Abbr. BW
In a general sense, this term describes the information-carrying
capacity of a given transmission medium. It is a measurement of
how much information can be carried in a given time period (usually
a second). It can apply to analog telephone (POTS), Ethernet
networks, digital computer system buses, radio frequency signals,
and VGA video signals used to connect projectors and monitors. See
our TechNote About Bandwidth
for more information.
baud rate (pronounced "bawd"; after Baudot
Code named for the French telegrapher Emile Baudot, 1845-1903)
The transmitted signaling speed, or keying rate of a modem. Often
confused with bit rate. Bit rate and
baud rat are NOT synonymous and shall not be interchanged in usage.
For example, one baud equals one half dot cycle per second in
Morse code, one bit per second in a train of binary signals, and
one 3-bit value per second in a train of signals each of which can
assume one of 8 different states, and so on - all brought to you
by the magic of advanced coding techniques that allow more than
one bit per baud. Preferred usage is bit rate, with baud
used only when the details of a modem are specified.
Baxandall tone controls
The most common form of active bass and treble tone control circuit
based upon British engineer P.J. Baxandall's paper "Negative
Feedback tone Control -- Independent Variation of Bass and Treble
Without Switches," Wireless World, vol. 58, no. 10,
October 1952, p. 402. The Baxandall design is distinguished by having
very low harmonic distortion due to the use of negative feedback.
BCD 1. (binary-coded decimal) Pertains to
a number system where each decimal digit is separately represented
by a 4-bit binary code; for example, the decimal number 23 is represented
as 0010 0011 (2 = 0010 and 3 = 0011, grouped together as shown),
while in straight binary notation, 23 is represented as 10111.
bel Abbr. b, B Ten decibels. [After
Alexander Graham Bell.] The Bel was the amount a signal
dropped in level over a one-mile distance of telephone wire. See:
Bell, Alexander Graham (1847-1922) Scottish-born
American inventor of the telephone. The first demonstration of electrical
transmission of speech by his apparatus took place in 1876. Bell
also invented the audiometer, an early hearing aid, and improved
Bessel crossover A type of
filter design characterized by having a linear phase response
(or maximally flat phase response), but also a
decreasing passband amplitude response
(which means it starts rolling off at DC and continues throughout
the passband). Linear phase response (e.g., a linear plot
of phase shift vs. frequency produces a straight line) results in
constant time-delay (all frequencies within the passband
are delayed the same amount). Consequently the value of linear phase
is it reproduces a near-perfect step response, i.e., there
is no overshoot or ringing resulting from a sudden transition between
signal levels. The drawback is a sluggish roll-off rate. For example,
for the same circuit complexity a Butterworth
response rolls off nearly three times as fast. This circuit
is based upon Bessel polynomials; however, the filters
whose network functions use these polynomials are correctly
called Thompson filters [W.E. Thomson, "Delay Networks
Having Maximally Flat Frequency Characteristics," Proc.
IEEE, part 3, vol. 96. Nov 1949, pp. 487-490].
binary A condition in which there are two possible states;
for example, the binary number system (base-2) using the digits
0 and 1.
bit Abbreviation for binary unit or binary digit.
The smallest amount of digital information. A bit can store or represent
only two states, 0 and 1. [The orginal term binary unit was
coined by John Tukey of Bell Laboratories to represent the basic
unit of information as defined by Shannon
as a message representing one of two states.]
bit clock The synchronizing signal that indicates the rate
of individual data bits over a digital audio interface.
bit error rate The number of bits processed before an erroneous
bit is found.
bit rate The rate or frequency at
which bits appear in a bit stream. The bit rate of raw data from
a CD, for example, is 4.3218 MHz.
bit stream A binary signal without regard to grouping.
bit-mapped display A display in which each
color and intensity data are stored in a separate memory location.
Bluetooth Early misunderstanding led many people to
believe Bluetooth was a wide-area networking solution.
Bluetooth is actually a short-run cable replacement, intended
originally to connect a cell phone to a headset and microphone.
Bluetooth is a trademark of L M Ericsson in Sweden. WPAN (Wide
Personal Area Network) is a trademark of the IEEE for the same
BNC (bayonet Neill Concelman, or
baby N-connector, or bayonet connector,
or bayonet Navy connector) A bayonet-locking connector
for slim coaxial cables. What "BNC" truly stands for is
still debated: 1) There is an "N-connector," similar
to, but larger than the BNC-type, used for fat coaxial cables; 2)
Neill Concelman is credited with inventing this connector;
3) It is a bayonet-style; 4) and many claim it was named
for the Navy who developed the connector for war-time communication
during WWII -- so, take your pick.
George (1815-1864) British mathematician who devised a new
form of algebra that represented logical expressions in a mathematical
form now known as Boolean Algebra. [See Maxfield in
boost/cut equalizer The most common
graphic equalizer. Available
with 10 to 31 bands, on 1-octave to
spacing. The flat (0 dB) position locates all sliders at the center
of the front panel. Comprised of bandpass filters, all controls
start at their center 0 dB position and boost (amplify or make larger)
signals by raising the sliders, or cut (attenuate or make smaller)
the signal by lowering the sliders on a band-by-band basis. Commonly
provide a center-detent feature identifying the 0 dB position. Proponents
of boosting in permanent sound systems argue that cut-only use requires
adding make-up gain which runs the same risk of reducing system
headroom as boosting.
Bps (Bits Per Second) A measure
(the amount of data that can flow in a given time). Bps is
defined as the number of bits per second that can
be transmitted over the specified data transmission medium.
BRI (Basic Rate Interface) An ISDN access or subscriber
line, consisting of two 64Kbps B (bearer) channels and a 16 Kbps D
channel. See ISDN
broadband digital link with a
broad bandwidth - that is, a broadband link -
generally, one that is capable of caring enough information to sustain the succession of images in
a video transmission (see Bandwidth). Technically a
channel in which a wide
band of frequencies is available
to transmit information.
buffer In data transmission, a temporary storage location
for information being sent or received.
bus An electrical conductor used for
transmitting signal or power from one or more sources to one or
Butterworth crossover A
type of crossover circuit utilizing
filter design characterized by having a maximally flat magnitude
response, i.e., no amplitude ripple in the
This circuit is based upon Butterworth functions (or Butterworth
polynomials). Named after S. Butterworth, a British engineer
who first described this response in his paper "On the Theory
of Filter Amplifiers," Wireless Engineer, vol. 7, 1930,
pp. 536-541. Eleven years later, V.D. Landon coined the phrase maximally
flat in his paper "Cascade Amplifiers with Maximal Flatness,"
RCA Review, vol. 5, 1941, pp. 347-362.]
byte A group of eight digital bits (a
word) operating together to represent one