Frequency Range of Music
*This chart only displays to a C0, though the octocontrabass clarinet extends down the B♭ below that C.
Wednesday, February 4, 2009
Speed of sound
Speed of sound
U.S. Navy F/A-18 breaking the sound barrier. The white halo is formed by condensed water droplets which are thought to result from a drop in air pressure around the aircraft (see Prandtl-Glauert Singularity).[2][3]
Main article: Speed of sound
The speed of sound depends on the medium through which the waves are passing, and is often quoted as a fundamental property of the material. In general, the speed of sound is proportional to the square root of the ratio of the elastic modulus (stiffness) of the medium to its density. Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in gases depends on temperature. In 20 °C (68 °F) air at the sea level, the speed of sound is approximately 343 m/s (1,230 km/h; 767 mph). In fresh water, also at 20 °C, the speed of sound is approximately 1,482 m/s (5,335 km/h; 3,315 mph). In steel, the speed of sound is about 5,960 m/s (21,460 km/h; 13,330 mph).[4] The speed of sound is also slightly sensitive (a second-order anharmonic effect) to the sound amplitude, which means that there are nonlinear propagation effects, such as the production of harmonics and mixed tones not present in the original sound (see parametric array).
Acoustics and noise
The scientific study of the propagation, absorption, and reflection of sound waves is called acoustics. Noise is a term often used to refer to an unwanted sound. In science and engineering, noise is an undesirable component that obscures a wanted signal.
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U.S. Navy F/A-18 breaking the sound barrier. The white halo is formed by condensed water droplets which are thought to result from a drop in air pressure around the aircraft (see Prandtl-Glauert Singularity).[2][3]
Main article: Speed of sound
The speed of sound depends on the medium through which the waves are passing, and is often quoted as a fundamental property of the material. In general, the speed of sound is proportional to the square root of the ratio of the elastic modulus (stiffness) of the medium to its density. Those physical properties and the speed of sound change with ambient conditions. For example, the speed of sound in gases depends on temperature. In 20 °C (68 °F) air at the sea level, the speed of sound is approximately 343 m/s (1,230 km/h; 767 mph). In fresh water, also at 20 °C, the speed of sound is approximately 1,482 m/s (5,335 km/h; 3,315 mph). In steel, the speed of sound is about 5,960 m/s (21,460 km/h; 13,330 mph).[4] The speed of sound is also slightly sensitive (a second-order anharmonic effect) to the sound amplitude, which means that there are nonlinear propagation effects, such as the production of harmonics and mixed tones not present in the original sound (see parametric array).
Acoustics and noise
The scientific study of the propagation, absorption, and reflection of sound waves is called acoustics. Noise is a term often used to refer to an unwanted sound. In science and engineering, noise is an undesirable component that obscures a wanted signal.
Perception of sound
Perception of sound
Human ear
For humans, hearing is limited to frequencies between about 20 Hz and 20,000 Hz (20 kHz), with the upper limit generally decreasing with age. Other species have a different range of hearing. For example, dogs can perceive vibrations higher than 20 kHz. As a signal perceived by one of the major senses, sound is used by many species for detecting danger, navigation, predation, and communication. Earth's atmosphere, water, and virtually any physical phenomenon, such as fire, rain, wind, surf, or earthquake, produces (and is characterized by) its unique sounds. Many species, such as frogs, birds, marine and terrestrial mammals, have also developed special organs to produce sound. In some species, these have evolved to produce song and speech. Furthermore, humans have developed culture and technology (such as music, telephone and radio) that allows them to generate, record, transmit, and broadcast sound.
Human ear
For humans, hearing is limited to frequencies between about 20 Hz and 20,000 Hz (20 kHz), with the upper limit generally decreasing with age. Other species have a different range of hearing. For example, dogs can perceive vibrations higher than 20 kHz. As a signal perceived by one of the major senses, sound is used by many species for detecting danger, navigation, predation, and communication. Earth's atmosphere, water, and virtually any physical phenomenon, such as fire, rain, wind, surf, or earthquake, produces (and is characterized by) its unique sounds. Many species, such as frogs, birds, marine and terrestrial mammals, have also developed special organs to produce sound. In some species, these have evolved to produce song and speech. Furthermore, humans have developed culture and technology (such as music, telephone and radio) that allows them to generate, record, transmit, and broadcast sound.
Channel-Associated versus Common-Channel
Channel-Associated versus Common-Channel
Channel-Associated signalling employs a signalling channel which is dedicated to a specific bearer channel.
Common-Channel signalling is so-called, because it employs a signalling channel which conveys signalling information relating to multiple bearer channels. These bearer channels therefore have Compelled Signalling
The term Compelled signalling refers to the case where receipt of each signal needs to be explicitly acknowledged before the next signal is able to be sent.
Most forms of R2 register signalling are compelled (see R2 signalling), while R1 multi-frequency is not.
The term is only relevant in the case of signalling systems that use discrete signals (e.g. a combination of tones to denote one digit), as opposed to signalling systems which are message-oriented (such as SS7 and ISDN Q.931) where each message is able to convey multiple items of information (e.g. multiple digits of the called telephone number).
Channel-Associated signalling employs a signalling channel which is dedicated to a specific bearer channel.
Common-Channel signalling is so-called, because it employs a signalling channel which conveys signalling information relating to multiple bearer channels. These bearer channels therefore have Compelled Signalling
The term Compelled signalling refers to the case where receipt of each signal needs to be explicitly acknowledged before the next signal is able to be sent.
Most forms of R2 register signalling are compelled (see R2 signalling), while R1 multi-frequency is not.
The term is only relevant in the case of signalling systems that use discrete signals (e.g. a combination of tones to denote one digit), as opposed to signalling systems which are message-oriented (such as SS7 and ISDN Q.931) where each message is able to convey multiple items of information (e.g. multiple digits of the called telephone number).
Line versus Register
Line versus Register
Line signaling is concerned with conveying information on the state of the line or channel, such as on-hook, off-hook (Answer supervision and Disconnect supervision, together referred to as supervision), ringing current (alerting), and recall. In the middle 20th Century, supervision signals on long distance trunks in North America were usually inband, for example at 2600 Hz, necessitating a notch filter to prevent interference. Late in the century, all supervisory signals were out of band. With the advent of digital trunks, supervision signals are carried by robbed bits or other bits in the digital stream dedicated to signalling.
Register signaling is concerned with conveying addressing information, such as the calling and/or called telephone number. In the early days of telephony, with operator handling calls, the addressing information is by voice as "Operator, connect me to Mr. Smith please". In the first half of the 20th century, addressing information is by using a rotary dial, which rapidly breaks the line current into pulses, with the number of pulses conveying the address. Finally, starting in the second half of the century, address signalling is by DTMF
Line signaling is concerned with conveying information on the state of the line or channel, such as on-hook, off-hook (Answer supervision and Disconnect supervision, together referred to as supervision), ringing current (alerting), and recall. In the middle 20th Century, supervision signals on long distance trunks in North America were usually inband, for example at 2600 Hz, necessitating a notch filter to prevent interference. Late in the century, all supervisory signals were out of band. With the advent of digital trunks, supervision signals are carried by robbed bits or other bits in the digital stream dedicated to signalling.
Register signaling is concerned with conveying addressing information, such as the calling and/or called telephone number. In the early days of telephony, with operator handling calls, the addressing information is by voice as "Operator, connect me to Mr. Smith please". In the first half of the 20th century, addressing information is by using a rotary dial, which rapidly breaks the line current into pulses, with the number of pulses conveying the address. Finally, starting in the second half of the century, address signalling is by DTMF
In-Band versus Out-Of-Band
In-Band versus Out-Of-Band
In the public switched telephone network, (PSTN), in-band signalling is the exchange of signalling (call control) information within the same channel that the telephone call itself is using. An example is DTMF 'Dual-Tone multi-frequency' signalling, which is used on most telephone lines to exchanges.
Out-of-band signalling is telecommunication signalling (exchange of information in order to control a telephone call) that is done on a channel that is dedicated for the purpose and separate from the channels used for the telephone call. Out-of-band signalling is used in Signalling System #7 (SS7), the standard for signalling among exchanges that has controlled most of the world's phone calls for some twenty years.
In the public switched telephone network, (PSTN), in-band signalling is the exchange of signalling (call control) information within the same channel that the telephone call itself is using. An example is DTMF 'Dual-Tone multi-frequency' signalling, which is used on most telephone lines to exchanges.
Out-of-band signalling is telecommunication signalling (exchange of information in order to control a telephone call) that is done on a channel that is dedicated for the purpose and separate from the channels used for the telephone call. Out-of-band signalling is used in Signalling System #7 (SS7), the standard for signalling among exchanges that has controlled most of the world's phone calls for some twenty years.
Signalling
Signalling (telecommunications)
From Wikipedia, the free encyclopedia
Jump to: navigation, search
In telecommunication, signalling (UK spelling) or signaling (US spelling) has the following meanings:
The use of signals for controlling communications.
In a telecommunications network, the information exchange concerning the establishment and control of a connection and the management of the network, in contrast to user information transfer.
The sending of a signal from the transmitting end of a circuit to inform a user at the receiving end that a message is to be sent.
Signalling systems can be classified according to their principal properties, some of which are described below:
Contents[hide]
1 In-Band versus Out-Of-Band
2 Line versus Register
3 Channel-Associated versus Common-Channel
4 Compelled Signalling
5 Subscriber versus trunk signalling
6 Classification examples
7 Sources
//
From Wikipedia, the free encyclopedia
Jump to: navigation, search
In telecommunication, signalling (UK spelling) or signaling (US spelling) has the following meanings:
The use of signals for controlling communications.
In a telecommunications network, the information exchange concerning the establishment and control of a connection and the management of the network, in contrast to user information transfer.
The sending of a signal from the transmitting end of a circuit to inform a user at the receiving end that a message is to be sent.
Signalling systems can be classified according to their principal properties, some of which are described below:
Contents[hide]
1 In-Band versus Out-Of-Band
2 Line versus Register
3 Channel-Associated versus Common-Channel
4 Compelled Signalling
5 Subscriber versus trunk signalling
6 Classification examples
7 Sources
//
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