Balanced - Revision history

Brad Johnson at 19:25, 28 August 2019

2019-08-28T19:25:00Z

Brad Johnson at 21:01, 11 April 2018

2018-04-11T21:01:04Z

Brad Johnson at 21:00, 11 April 2018

2018-04-11T21:00:34Z

Brad Johnson: /* Overview */

2018-04-11T20:58:30Z

Overview

Brad Johnson at 22:57, 2 August 2017

2017-08-02T22:57:20Z

Brad Johnson at 22:49, 2 August 2017

2017-08-02T22:49:11Z

Brad Johnson at 00:46, 21 February 2017

2017-02-21T00:46:34Z

Brad Johnson at 00:43, 21 February 2017

2017-02-21T00:43:39Z

Brad Johnson at 00:42, 21 February 2017

2017-02-21T00:42:25Z

Brad Johnson at 00:41, 21 February 2017

2017-02-21T00:41:02Z

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 There are two types of coaxial unbalanced digital audio connections: professional and consumer. The professional standard is part of the same AES3 standard as the differential, with the signal format being the same; but the connection is made using 75 Ohm [[BNC]] coaxial cable and connectors. The signal voltage is also nominal "5 volt" before termination. This format allows reliable operation with cable lengths up to 100 meters.
-The consumer format is the same as the original S-PDIF format; which has been superseded by the IEC 60958 type II standard. Connections are made using 75 Ohm coaxial cable; most frequently with [[RCA]] connectors. The signal voltage is nominal 1 Volt before termination. Part of the limitation of the unbalanced consumer format is the relatively low signal voltage of less than one-half volt after termination. The combination of low signal voltage with unbalanced connections places severe length limitations on consumer coaxial digital audio connections. It is recommended that cable lengths be kept below 3 meters whenever possible. With longer cable lengths; it is very important that some form of common ground besides the coaxial connection be present; such as plugging both the sending and receiving device into a common AC power source with 3-prong AC cords.
+The consumer format is the same as the original S-PDIF format; which has been superseded by the [[IEC 60958 type II]] standard. Connections are made using 75 Ohm coaxial cable; most frequently with [[RCA]] connectors. The signal voltage is nominal 1 Volt before termination. Part of the limitation of the unbalanced consumer format is the relatively low signal voltage of less than one-half volt after termination. The combination of low signal voltage with unbalanced connections places severe length limitations on consumer coaxial digital audio connections. It is recommended that cable lengths be kept below 3 meters whenever possible. With longer cable lengths; it is very important that some form of common ground besides the coaxial connection be present; such as plugging both the sending and receiving device into a common AC power source with 3-prong AC cords.
 The same length restrictions apply to the use of adapters or adapter cables to connect Consumer level digital audio sources to Lavry XLR digital audio inputs.

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 In order to minimize noise pick-up by long cables carrying low level signal such as those output by a microphone, a system of transmission was developed using audio "signal" transformers. One of the advantages of an [[audio transformer]] is that there is no physical connection between the input circuit ("primary coil") and the output circuit ("secondary").
-Before audio electronics were developed that worked on [[bipolar]]power supplies; some method was needed to isolate the [[DC]] voltages required for audio circuits operating on "single-ended" DC power from different stages of the circuitry and from devices connected to the input and output. In many cases; "coupling capacitors" were used to allow the [[AC]] (audio signal) to pass while "blocking" the DC. In some cases, transformers could also serve this function; and provided other useful functions such as [[impedance]] and level matching.
+Before audio electronics were developed that worked on [[bipolar]] power supplies; some method was needed to isolate the [[DC]] voltages required for audio circuits operating on "single-ended" DC power from different stages of the circuitry and from devices connected to the input and output. In many cases; "coupling capacitors" were used to allow the [[AC]] (audio signal) to pass while "blocking" the DC. In some cases, transformers could also serve this function; and provided other useful functions such as [[impedance]] and level matching.
 A microphone can have a transformer in its output with a "floating" secondary (output). This means simply that neither of the two signal conductors is referenced to ground. At the input of the microphone preamp; there was a second transformer that contains a primary with a "center-tap" which referenced the center of the winding to ground. As a result; the signals in the two signal conductors would be the "same" except that they were of opposite [[polarity]]. The ground reference provided by the center-tap of the micpre input transformer caused the signal voltages to be "centered" on ground (of equal positive and negative voltage range).

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 In order to minimize noise pick-up by long cables carrying low level signal such as those output by a microphone, a system of transmission was developed using audio "signal" transformers. One of the advantages of an [[audio transformer]] is that there is no physical connection between the input circuit ("primary coil") and the output circuit ("secondary").
-Before audio electronics were developed that worked on power supplies with both "plus" and "minus" voltages; some method was needed to isolate the DC voltages required for audio circuits operating on "single-ended" DC power from different stages of the circuitry and from devices connected to the input and output. In many cases; "coupling capacitors" were used to allow the AC (audio signal) to pass while "blocking" the DC. In some cases, transformers could also serve this function; and provided other useful functions such as [[impedance]] and level matching.
+Before audio electronics were developed that worked on [[bipolar]]power supplies; some method was needed to isolate the [[DC]] voltages required for audio circuits operating on "single-ended" DC power from different stages of the circuitry and from devices connected to the input and output. In many cases; "coupling capacitors" were used to allow the [[AC]] (audio signal) to pass while "blocking" the DC. In some cases, transformers could also serve this function; and provided other useful functions such as [[impedance]] and level matching.
 A microphone can have a transformer in its output with a "floating" secondary (output). This means simply that neither of the two signal conductors is referenced to ground. At the input of the microphone preamp; there was a second transformer that contains a primary with a "center-tap" which referenced the center of the winding to ground. As a result; the signals in the two signal conductors would be the "same" except that they were of opposite [[polarity]]. The ground reference provided by the center-tap of the micpre input transformer caused the signal voltages to be "centered" on ground (of equal positive and negative voltage range).

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 ==Overview==
-The term "<nowiki>Balanced</nowiki>" is used in audio to describe a form of signal transmission utilizing two signal conductors that carry signals which are both: a.) identical except for being of opposite [[polarity]] and b.) of equal positive and negative voltage amplitude (the voltage [[waveform]] varies equally above and below signal [[ground]].
+The term "<nowiki>Balanced</nowiki>" is used in audio to describe a form of signal transmission utilizing two signal conductors that carry signals which are both: a.) identical except for being of opposite [[polarity]] and b.) of equal positive and negative [[voltage]] [[amplitude]] range (the voltage [[waveform]] can vary equally above and below signal [[ground]].
 ==History==

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 The other form of interference is "noise" induced by electromagnetic or electrostatic interference on the audio cable's shield. In the case of an Unbalanced connection; the shield must be connected directly to the audio input of the receiving device to provide the [[signal return]] path for the audio signal on the center conductor. Balanced connections allow the shield to be connected to a ground that is isolated from the input audio signal path; or in more extreme cases involving ground loops; to not be connected ''at all'' to the input device when another ground connection provides the necessary reference.
-The important aspect of a balanced input is that it is "differential." One input is [[non-inverting]] and amplifies the signal with the original [[polarity]]. The other input is [[inverting]] and amplifies its input signal with the opposite polarity. What makes it work as a system to amplify the desired (audio) signal and cancel the interference (hum and noise) is the fact that the balanced output is configured in the same manner. The output that is inverted feeds the input that is inverted, and the result is the inversion is eliminated and the signal from both inputs are added together "in-phase." This results in an output from the balanced input stage that is the same polarity as the non-inverted output. Noise and interference signals appear with the 'same polarity on both signal conductors, so when the differential input inverts one of these signals and adds it with the non-inverted signal they cancel each other. See [[Waveform]] for more information on “phase-cancellation.”
+The important aspect of a balanced input is that it is "differential." One input is [[non-inverting]] and amplifies the signal with the original [[polarity]]. The other input is [[inverting]] and amplifies its input signal with the opposite polarity. What makes it work as a system to amplify the desired (audio) signal and cancel the interference (hum and noise) is the fact that the balanced output is configured in the same manner. The output that is inverted feeds the input that is inverted, and the result is the inversion is eliminated and the signal from both inputs are added together "in-phase." This results in an output from the balanced input stage that is the same polarity as the non-inverted output. Noise and interference signals appear with the ''same'' polarity on both signal conductors, so when the differential input inverts one of these signals and adds it with the non-inverted signal they cancel each other. See [[Waveform]] for more information on “phase-cancellation.”
 Balanced outputs that employ audio transformers are typically "floating," in that neither of the transformer's output conductors are connected to audio ground. This allows either of the two signal conductors to be connected to ground when feeding an unbalanced input. Because the entire signal voltage appears across the input in either balanced or unbalanced connections; there is also no difference in level if the transformer-equipped balanced output is "unbalanced" by the wiring or connection to an unbalanced input. The down-side is that even very expensive high-quality audio transformers are non-linear compared to contemporary audio amplifiers, and are not "DC coupled.”

← Older revision		Revision as of 00:46, 21 February 2017
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	There are two types of coaxial unbalanced digital audio connections: professional and consumer. The professional standard is part of the same AES3 standard as the differential, with the signal format being the same; but the connection is made using 75 Ohm [[BNC]] coaxial cable and connectors. The signal voltage is also nominal "5 volt" before termination. This format allows reliable operation with cable lengths up to 100 meters.		There are two types of coaxial unbalanced digital audio connections: professional and consumer. The professional standard is part of the same AES3 standard as the differential, with the signal format being the same; but the connection is made using 75 Ohm [[BNC]] coaxial cable and connectors. The signal voltage is also nominal "5 volt" before termination. This format allows reliable operation with cable lengths up to 100 meters.

−	The consumer format is the same as the original S-PDIF format; which has been superseded by the IEC 60958 type II standard. Connections are made using 75 Ohm coaxial cable; most frequently with RCA connectors. The signal voltage is nominal 1 Volt before termination. Part of the limitation of the unbalanced consumer format is the relatively low signal voltage of less than one-half volt after termination. The combination of low signal voltage with unbalanced connections places severe length limitations on consumer coaxial digital audio connections. It is recommended that cable lengths be kept below 3 meters whenever possible. With longer cable lengths; it is very important that some form of common ground besides the coaxial connection be present; such as plugging both the sending and receiving device into a common AC power source with 3-prong AC cords.	+	The consumer format is the same as the original S-PDIF format; which has been superseded by the IEC 60958 type II standard. Connections are made using 75 Ohm coaxial cable; most frequently with [[RCA]] connectors. The signal voltage is nominal 1 Volt before termination. Part of the limitation of the unbalanced consumer format is the relatively low signal voltage of less than one-half volt after termination. The combination of low signal voltage with unbalanced connections places severe length limitations on consumer coaxial digital audio connections. It is recommended that cable lengths be kept below 3 meters whenever possible. With longer cable lengths; it is very important that some form of common ground besides the coaxial connection be present; such as plugging both the sending and receiving device into a common AC power source with 3-prong AC cords.

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 In order to minimize interference caused by very high frequency signals "reflecting" at points of [[impedance]] miss-match; any signal path of significant length must be "impedance matched." By having the value of the cable's characteristic impedance "terminating" both the transmitting end and the receiving end; reflections are minimized. In the case of digital audio, this value is 75 Ohms for [[coaxial]] connections and 110 Ohms for differential connections.
-There are two types of coaxial unbalanced digital audio connections: professional and consumer. The professional standard is part of the same AES3 standard as the differential, with the signal format being the same; but the connection is made using 75 Ohm BNC coaxial cable and connectors. The signal voltage is also nominal "5 volt" before termination. This format allows reliable operation with cable lengths up to 100 meters.
+There are two types of coaxial unbalanced digital audio connections: professional and consumer. The professional standard is part of the same AES3 standard as the differential, with the signal format being the same; but the connection is made using 75 Ohm [[BNC]] coaxial cable and connectors. The signal voltage is also nominal "5 volt" before termination. This format allows reliable operation with cable lengths up to 100 meters.
 The consumer format is the same as the original S-PDIF format; which has been superseded by the IEC 60958 type II standard. Connections are made using 75 Ohm coaxial cable; most frequently with RCA connectors. The signal voltage is nominal 1 Volt before termination. Part of the limitation of the unbalanced consumer format is the relatively low signal voltage of less than one-half volt after termination. The combination of low signal voltage with unbalanced connections places severe length limitations on consumer coaxial digital audio connections. It is recommended that cable lengths be kept below 3 meters whenever possible. With longer cable lengths; it is very important that some form of common ground besides the coaxial connection be present; such as plugging both the sending and receiving device into a common AC power source with 3-prong AC cords.

@@ Line 42: / Line 42: @@
 The current [[AES]]/EBU standard for differential circuits does include the use of signal transformers at the output and input; so the connection does retain the "floating" quality. This is why Lavry AES/[[XLR]] digital input/output ("I/O") can be safely adapted to unbalanced connections for use with most unbalanced [[RCA]]/[[S-PDIF]] I/O using simple wired [[adapter]]s or [[adapter cable]]s. The difference between the 75 Ohm and 110 Ohm impedance of the two formats has a negligible effect with short cable lengths.
-In order to minimize interference caused by very high frequency signals "reflecting" at points of impedance miss-match; any signal path of significant length must be "impedance matched." By having the value of the cable's characteristic impedance "terminating" both the transmitting end and the receiving end; reflections are minimized. In the case of digital audio, this value is 75 Ohms for [[coaxial]] connections and 110 Ohms for differential connections.
+In order to minimize interference caused by very high frequency signals "reflecting" at points of [[impedance]] miss-match; any signal path of significant length must be "impedance matched." By having the value of the cable's characteristic impedance "terminating" both the transmitting end and the receiving end; reflections are minimized. In the case of digital audio, this value is 75 Ohms for [[coaxial]] connections and 110 Ohms for differential connections.
 There are two types of coaxial unbalanced digital audio connections: professional and consumer. The professional standard is part of the same AES3 standard as the differential, with the signal format being the same; but the connection is made using 75 Ohm BNC coaxial cable and connectors. The signal voltage is also nominal "5 volt" before termination. This format allows reliable operation with cable lengths up to 100 meters.

@@ Line 40: / Line 40: @@
 With 5 volt DC power; in the absence of a signal transformer, the output voltage can only vary between "0 volts" (or [[ground]]) and 5 volts. In reality; the output voltage cannot even reach 5 volts because there is always going to be some voltage "drop" across the transistor driving the output, and [[termination]] divides what is left in half. But the important point is that the signal voltage does not ever enter the negative voltage range and this type of circuitry is therefore referred to as "differential" as versus "balanced." It still employs the basic qualities of having two equal amplitude signals of opposite polarity carried on shielded twisted-pair cables with XLR connectors.
-The current [[AES]]/EBU standard for differential circuits does include the use of signal transformers at the output and input; so the connection does retain the "floating" quality. This is why Lavry AES/[[XLR]] digital input/output ("I/O") can be safely adapted to unbalanced connections for use with most unbalanced [[RCA]]/[[S-PDIF]] I/O using simple wired [[adapters]] or [[adapter cables]]. The difference between the 75 Ohm and 110 Ohm impedance of the two formats has a negligible effect with short cable lengths.
+The current [[AES]]/EBU standard for differential circuits does include the use of signal transformers at the output and input; so the connection does retain the "floating" quality. This is why Lavry AES/[[XLR]] digital input/output ("I/O") can be safely adapted to unbalanced connections for use with most unbalanced [[RCA]]/[[S-PDIF]] I/O using simple wired [[adapter]]s or [[adapter cable]]s. The difference between the 75 Ohm and 110 Ohm impedance of the two formats has a negligible effect with short cable lengths.
 In order to minimize interference caused by very high frequency signals "reflecting" at points of impedance miss-match; any signal path of significant length must be "impedance matched." By having the value of the cable's characteristic impedance "terminating" both the transmitting end and the receiving end; reflections are minimized. In the case of digital audio, this value is 75 Ohms for [[coaxial]] connections and 110 Ohms for differential connections.