Talk:Balanced audio

From Wikipedia, the free encyclopedia

	This article is within the scope of the Professional sound production WikiProject, a collaborative effort to improve Wikipedia's coverage of the technology, equipment, companies and professions related to professional sound production. If you would like to participate, you can visit the project page, where you can join the project and see a list of open tasks.
Start	This article has been rated as Start-Class on the assessment scale.

[edit] Article needs a topic sentence

This article begins

Balanced audio connections are extremely important in sound recording and production because...

What's needed is a definition. I don't know enough about the subject to make one (that's why I came here!). Jer ome 19:49, 28 March 2007 (UTC)

[edit] Incorrect

The article states that differential signalling is responsible for the noise rejection, but this is a common misconception. The noise will couple into both lines regardless of whether there's a differential signal on the lines or not. The feature that's important to common mode rejection is the impedance of the lines to ground.

This is the basis of "impedance balancing" or "quasi-balanced" connections (which we really need to cover in this article), in which the tip and ring are both terminated with the same impedance, but the ring goes to ground instead of an inverted source.

See Talk:Differential_signaling#Accuracy and Talk:Balanced_line#Accuracy for parallel discussion. — Omegatron 18:13, 22 May 2007 (UTC)

I'm a little rusty on the differences between near-field inductive and capacitive coupling, and far-field electromagnetic coupling:

Twisted pairs are primarily for rejecting inductive interference, right? You are minimizing the loop area so that a changing magnetic field induces less, and alternating the loop direction so that a changing magnetic field that induces equally through two adjacent loops causes equal and opposite currents, which cancel out. Does this technique have any effect on other types of interference?

Twisted pairs reduce inductive interference, but also cut down on capacitive crosstalk. --Heron 17:48, 26 May 2007 (UTC)

That's another reason for differential signalling, though not as applicable to audio? Audio is relatively low frequency and signals almost always travel alone and shielded, but in other cables, twisted pairs are routed next to each other. Differential signalling minimizes the EM from the pairs so that they don't couple into each other or into other devices. — Omegatron 15:56, 31 May 2007 (UTC)

And impedance balancing is more for capacitive interference? A changing electric field near a cable would create a similar effect on both lines, it would seem. Does impedance balancing also affect the other types of interference?

The mechanism of crosstalk depends on frequency. At LF it is mostly capacitive, and at HF the inductive effect takes over. --Heron 17:48, 26 May 2007 (UTC)

Shielding is more for electromagnetic interference, right? From RF and such? It's a type of Faraday cage, and so protects from electrostatic fields but not magnetostatic fields, and has varying effect on higher frequencies? See Talk:Faraday_cage#Mesh_size.3B_explanation.3B_magnetic_fields for the same discussion in a more general context. — Omegatron 15:12, 24 May 2007 (UTC)

Shielding is also used to reduce crosstalk (both capacitive and inductive). --Heron 17:48, 26 May 2007 (UTC)

Hmmm... Crosstalk between the two wires in a balanced audio connection would just mean a decrease in level? Though it might vary with frequency.

An ungrounded shield or chassis actually increases crosstalk between things that are inside it, though, because they couple to each other capacitively through the shield. — Omegatron 16:20, 31 May 2007 (UTC)

}} — Omegatron 21:28, 24 May 2007 (UTC)

And the ability to interface with a shorted pin 2 is actually somewhat important, because of the pin 2/3 = hot problem. — Omegatron 04:29, 25 May 2007 (UTC)

The article seems OK now in the area of differential versus balanced. (I'm ignoring the disputed section on amplifier internals, since I don't know much about that.) I found some notes from a seminar on EMC, and added some comments to your points above. Unfortunately it seems that you can't easily separate E, M and EM when it comes to protecting against them. --Heron 17:48, 26 May 2007 (UTC)