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Grounding and Interfacing
Published in Douglas Self, Audio Engineering Explained, 2012
An interface is a signal transport subsystem consisting of three components: a driver (one device's output), a line (interconnecting cable), and a receiver (another device's input). These components are connected to form a complete circuit for signal current, which requires a line having two signal conductors. The impedances of the signal conductors, usually with respect to ground, are what determine whether an interface is balanced or unbalanced. A concise definition of a balanced circuit is: A balanced circuit is a two-conductor circuit in which both conductors and all circuits connected to them have the same impedance with respect to ground and to all other conductors. The purpose of balancing is to make the noise pickup equal in both conductors, in which case it will be a common-mode signal that can be made to cancel out in the load (Ott, 1988, p. 118.)
Analogue Sound Mixing Equipment
Published in Michael Talbot-Smith, Sound Engineer's Pocket Book, 2013
The important point about balanced circuits is that the two legs are electrically identically similar, so that any induced interference will produce, ideally, exactly equal voltages in each leg. These are in opposition and therefore will ‘cancel out’. Perfect balancing is almost impossible, even if only because the two conductors inside the cable can never be at exactly the same distances from the sources of interference. Twisting the conductors improves matters and in one type of microphone cable (‘star quad’) four twisted conductors are used, opposite conductors being used for each leg. Such an arrangement gives very good immunity to the effects of interference, but even so 100 per cent protection can never be guaranteed.
Acoustics and acoustic devices
Published in Michael Talbot-Smith, Audio Engineer's Reference Book, 2012
Audio signals, being very low in level (0 dBu is 775 mV) are very susceptible to interference from stray electrical and magnetic fields, e.g. lighting and power circuits, motors, etc. An unbalanced connection uses a single conductor for the signal, with the return current passing either through a coaxial wire mesh screen (as in a phono or 2-pole jack plug) or via a second unscreened wire (as in loudspeaker leads). Such a system has poor protection from external interference, and as the second conductor is usually connected to the `ground planes' of the signal source and amplifier, a `hum loop' will ensue if these two ground planes are also connected externally, as happens when both items are earthed via mains connections. If the hum is cured by disconnecting the loop, the two ground planes may be at different potentials which in turn causes distortion of the signal. A balanced circuit uses two wires, one send and one return, both insulated from ground and connected to the equipment at each end by transformers (or their electronic equivalent) such that any interference (which is assumed to be picked up identically by both wires) is cancelled out (see Figure 2.96 ). This effect is enhanced by the two wires being twisted tightly together and covered by a conductive sheath of wire mesh or foil which is grounded at one end – a screened twin or pair. In addition, this arrangement isolates the different ground potentials, preventing the difference appearing as a signal, and is a major factor in eliminating ground loops (a major cause of hum) between connected items of equipment. Microphones (except for some domestic types) are invariably `balanced', as is most professional linelevel equipment; amplifiers and other circuits within mixers are generally unbalanced, so that transformers or electronic balanced/unbalanced converters are required at the inputs and outputs of mixers.
Tunable balanced liquid crystal phase shifter based on spoof surface plasmon polaritons with common-mode suppression
Published in Liquid Crystals, 2020
Chang Ding, Fan-Yi Meng, Tao Jin, Jian-Feng lv, Hui-Lin Mu, Qun Wu
In balanced circuit systems, the main electromagnetic interference is the so-called CM noise [21], which seriously degrades the signal-to-noise ratio (SNR). Thus, in the design of this proposed tunable balanced LCPS shown in Figure 2, by symmetrically etching slotted dumbbell-shaped resonators, the CM filtering function is efficiently achieved while the differential signal propagation is preserved.