Beginners Guide – Signal Chain

This is going to be the first ‘beginners guide’ to sound post. I don’t intend to go into too much detail, as I d often do training sessions with groups, that go into more detail. If your interested in that, get in contact.

So short and sweet it is!

Instrument / Vocals

Mic / DI

XLR Cable

Stagebox

Multicore

Desk; 

Gain – EQ – Aux’s – Pan – Fader

Main Output

Return Channel on Multicore

Amplifier

Speaker Cable

Speaker(s)

Note that this is a basic, simplified system, assuming you don’t have a desk with Inserts / Groups / VCA’s /  Matrixes  or heaps of processing / Outboard.

Starting at the top, the source is anything from a DJ’s laptop to a Violin Quartet, this is then either mic’d up or DI’d.

Microphones are the man made version of an ear, they just like the ear have a diaphragm, this vibrates when sound is received by it just like our ear drums, it is then translated into electrical energy and sent over the cables to the desk, at the other end of the system is a speaker (or several) which converts it back from electrical to kinetic energy.

DI or Direct Box changes an unbalanced signal into a balanced one. These are usually used for Keyboards, Laptops, Bass Guitars (normally as a split before the Amp). DI’s can be split into two types, Passive and Active, very simply one requires power (normally from the desk or 9v battery) to power the circuit, and the other uses a non powered transformer. Both have their advantages. But thats a different and far more complex topic for later.

XLR’s have 3 pins for Audio, 2 pins give the signal from the source, while the third Earths (grounds to the sound desk) / Sends Power back the other way (if needed) to power DI’s & Condenser Mics.

StageBox & Multicore- Normally you will find a black box sitting on the stage used to plug the XLR’s into, make sure that the numbers on the Desk end of the multi correspond to the stage end. Its usual for them to be numbered 1-16+, with the returns labelled 1-4+ or A, B, C, D, etc.

Desk, a sound desk used to be huge, carried by 6 people and weighed a ton! Nowadays the technology has come on a long way, and even large format Analogue Consoles are easier to lift with two people. With the recent advances in the Digital arena, a 32 ch desk can be picked up in one hand. Many options are out there, but all will have these basic features that I’ll cover here.

Channel Strip

Gain – This is a preamp, allowing the correct level to be set and the rest of the channel to work properly. If the gain is too low, the fader will sit max’d out, and you’ll find yourself boosting rather than cutting and causing issues with running your amps hotter. If the gain is too high, then the fader will be at it’s lowest, and still have issues with too much volume. There is a whole post about this coming, so I shall leave it till then.

– Note that Gain affects all other aspects of the system, and is commonly the place where people mess up. –

EQ & High Pass – Normally split up in to High, Mids and Lows, for each channel. allowing you to cut out offending frequencies, and boost pleasant frequencies. Personally I only use Subtractive rather than Additive EQ in a live situation, as there is room noise, and other issues. Again this will be covered in a later post. Most desks have a High pass Filter button, when activated, it removes the lowest frequencies, helping to reduce stage noise from walking around, touching the mic stand, and Plosives from ‘P’ words.

Aux’s are a way of sending that channel out to various locations. This could be out to a Reverb / Delay Unit for Vocals, or to InEars or Wedges on stage. They work in the same way that the Fader does, just a knob takes up less room. Some larger analogue desks, and almost all digital desks allow stereo Auxiliaries, meaning one knob would be volume of the left ear, and the other the right (in the case of InEars), or alternatively one is volume and the other is Pan.

Pan the last point referenced Pan, its simply the mix going between the Left and Right (in the case of stereo). Having the Pan pot in the centre means an equal amount is sent to each side. Having the pot panned all the way to the Left means that signal is only going to Left speaker, etc. This can become especially useful for when a presenter walks in front of the Left speaker, to avoid feedback, you can pan to the right speaker, allowing the message to still be audible in the room.

Fader this is the last part of the Channel Strip. It gives the user a great visual as to the channels in use, and where most beginners should spend their time. It controls the volume of the channel in the House Mix. its good practice to have your faders that are in use at Unity (marked O on most desks), this is the place where you have the most control. Its worth explaining that all the Aux pots, and Faders work logarithmically not linearly. Simply this means that its a curve that goes up rather than a straight line. 1 inch moved from the bottom of the fader would increase the volume by around 40dB, where as at Unity movement of an inch would result in 5(ish)dB change.

Main Outputs – Inside the desk, there are a variety of ways to send to the speakers. However this post will use the most basic. Either the desk will automatically send to the master outputs, or you will have to assign the channels individually via a button. You should know how to do this already, otherwise consult the manual! These like the channel Faders should be left at Unity. Although if your feeling creative, try starting the set with the faders a -5dB and gradually bringing them up to +3dB over the set. This helps to add more dynamics as the gig goes on.

Return Channel on Multicore, simply sending back out of the desk, and along the multicore in the other direction, back to the stage box, which is then send out to the Amplifiers and Speaker Processing (which we won’t discuss here).

Amplifier – This is covered partially in the Wedges Vs InEars Post. Basically there are two main types Amplifier, Digital ones, which allow speaker processing to be done in the box, and Analogue ones which do not. Amps basically increase the volume that the desk puts out into a large enough signal for the speakers to recognise.

Speaker Cables are usually thicker than XLR’s as they carry a larger load of energy, at a lower impedance than instrument cables. Normally they are either 2 core, or 4 core. This is for +1, -1, & +2, -2. EP5 has an extra pin, which can be used by the amp to monitor the speakers performance.

Speaker(s) I covered Active vs Passive in a previous post, which your free to read at your leisure. As I stated earlier speakers transfer the electrical energy back to Kinetic (movement) energy. By moving the air it reproduces the sound waves that hit the microphone. Placement is important, in front of the mics and instruments and giving a stereo spread helps to give width to the mix.

So there you are! A brief summary, although I’ve disclosed more than originally planned! Let me know what you think in the comments section and look out for more to coming out shortly.

 

Published by danbamberaudio

Freelance Project Manager / Sound Engineer / AV Tech based in Manchester UK.

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