In brief, the
passband is the range of frequencies or wavelengths that can pass through a
filterIn signal processing, a filter is a device or process that removes from a signal some unwanted component or feature. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal...
without being attenuated.
In telecommunications,
opticsOptics is the branch of physics which studies the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
, and
acousticsAcoustics is the interdisciplinary science that deals with the study of sound, ultrasound and infrasound . A scientist who works in the field of acoustics is an acoustician. The application of acoustics in technology is called acoustical engineering...
, a
passband is the portion of spectrum (not to be confused with
band-passA band-pass filter is a device that passes frequencies within a certain range and rejects frequencies outside that range. An example of an analogue electronic band-pass filter is an RLC circuit...
), between
limitingLimiting: Any process by which a specified characteristic of the output of a device is prevented from exceeding a predetermined value....
frequencies (or, in the optical regime, limiting wavelengths), that is transmitted with minimum relative loss or maximum relative
gainGain is a measure of a system's response to feedback. If the gain in a positive feedback loop is less than 1, the feedback is not of itself sufficient to make the system become unstable. For example, water evaporating from the World's oceans causes a positive feedback, as it is a greenhouse gas...
by a filtering device.
There are two main categories of digital communication transmission methods:
basebandIn telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from zero to a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies starting at zero...
and
passband.
- In baseband transmission, line coding is utilized, resulting in a pulse train or pulse amplitude modulated (PAM) signal.
In brief, the
passband is the range of frequencies or wavelengths that can pass through a
filterIn signal processing, a filter is a device or process that removes from a signal some unwanted component or feature. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal...
without being attenuated.
Passband in terms of filters
In telecommunications,
opticsOptics is the branch of physics which studies the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
, and
acousticsAcoustics is the interdisciplinary science that deals with the study of sound, ultrasound and infrasound . A scientist who works in the field of acoustics is an acoustician. The application of acoustics in technology is called acoustical engineering...
, a
passband is the portion of spectrum (not to be confused with
band-passA band-pass filter is a device that passes frequencies within a certain range and rejects frequencies outside that range. An example of an analogue electronic band-pass filter is an RLC circuit...
), between
limitingLimiting: Any process by which a specified characteristic of the output of a device is prevented from exceeding a predetermined value....
frequencies (or, in the optical regime, limiting wavelengths), that is transmitted with minimum relative loss or maximum relative
gainGain is a measure of a system's response to feedback. If the gain in a positive feedback loop is less than 1, the feedback is not of itself sufficient to make the system become unstable. For example, water evaporating from the World's oceans causes a positive feedback, as it is a greenhouse gas...
by a filtering device.
Passband in terms of digital transmission
There are two main categories of digital communication transmission methods:
basebandIn telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from zero to a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies starting at zero...
and
passband.
- In baseband transmission, line coding is utilized, resulting in a pulse train or pulse amplitude modulated (PAM) signal. This is typically utilized over non-filtered wires such as fiber optical cables and short-range copper cables, for example serial cables and LAN networks.
- The passband transmission, digital modulation methods are utilized in view to only utilize a limited frequency band over a passband filtered channel. Passband transmission is typically utilized in wireless communication and in passband filtered channels such as the analogue telephone access network. It also allows frequency division multiplex. The digital bit-stream is converted first into an equivalent baseband
In telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from zero to a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies starting at zero...
signal (often a complex-valued signal), and then to a Radio FrequencyRadio frequency is a frequency, or rate of oscillation, of electromagnetic radiation within the range of about 3 Hz to 300 GHz. This range corresponds to the frequency of alternating current electrical signals used to produce and detect radio waves...
(RF) signal. On the receiver side a demodulator is used to detect the signal. A combined equipment for modulation and demodulation is called modemModem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
.
Overview
RadioRadio is the transmission of signals by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
receivers generally include a tunable
band-pass filterA band-pass filter is a device that passes frequencies within a certain range and rejects frequencies outside that range. An example of an analogue electronic band-pass filter is an RLC circuit...
with a passband that is wide enough to accommodate the bandwidth of the radio signal transmitted by a single station.
Passbands are found in many systems outside of telecommunications. For example, most traditional musical instruments are tunable sonic
band-pass filterA band-pass filter is a device that passes frequencies within a certain range and rejects frequencies outside that range. An example of an analogue electronic band-pass filter is an RLC circuit...
s with narrow passbands. Woodwind instruments such as the
fluteThe flute is a musical instrument of the woodwind group. Unlike woodwind instruments with reeds, a flute is an aerophone or reedless wind instrument that produces its sound from the flow of air across an opening...
and penny whistle are good examples: the flute is stimulated by broad-band sonic noise at the
mouthpieceThe mouthpiece of a woodwind instrument is that part of the instrument which is placed partly in the player's mouth. Single-reed instruments, capped double-reed instruments, and fipple flutes have mouthpieces while exposed double-reed instruments and open flutes do not.-Single-reed instruments:On...
but resonates only in a narrow passband around the fingered note.
OverblowingOverblowing is a technique used in playing a wind instrument to produce a different pitch by changing the direction and/or force of the air stream to disturb the fundamental of a note and let one of the overtones of the note to dominate...
a flute (that is, playing higher notes with the same fingering as a lower note) is possible because the flute has multiple passbands for any given fingering: the note that emerges is dependent on both the fingering and the spectrum of wind noise at the mouthpiece.
In general, there is an inverse relationship between the width of a filter's passband and the time required for the filter to respond to new inputs. Broad passbands yield faster response. This is a consequence of the
mathematicsMathematics is the science and study of quantity, structure, space, and change. Mathematicians seek out patterns, formulate new conjectures, and establish truth by rigorous deduction from appropriately chosen axioms and definitions....
of Fourier analysis.
Note 1: The limiting frequencies are defined as those at which the relative intensity or
powerIn physics, power is the rate at which work is performed or energy is converted. It is an energy per unit of time. As a rate of change of work done or the energy of a subsystem, power iswhere P is power, W is work and t is time....
decreases to a specified fraction of the maximum intensity or power. This decrease in power is often specified to be the half-power points,
i.e., 3
dBThe decibel is a logarithmic unit of measurement that expresses the magnitude of a physical quantity relative to a specified or implied reference level. Since it expresses a ratio of two quantities with the same unit, it is a dimensionless unit...
below the maximum power.
Note 2: The difference between the limiting frequencies is called the bandwidth, and is expressed in
hertzThe hertz is a unit of frequency. It is defined as the number of complete cycles per second. It is the basic unit of frequency in the International System of Units , and is used worldwide in both general-purpose and scientific contexts...
(in the optical regime, in nanometers or micrometers of differential wavelength).
Note 3: The related term "bandpass" is an adjective that describes a type of filter or filtering process; it is frequently confused with "passband", which refers to the actual portion of affected spectrum. The two words are both
compound wordsIn linguistics, a compound is a lexeme that consists of more than one stem. Compounding or composition is the word-formation that creates compound lexemes...
that follow the English rules of formation: the primary meaning is the latter part of the compound, while the modifier is the first part. Hence, one may correctly say 'A dual bandpass filter has two passbands'.