WILLY T gets some action with AUXILIARY SENDS, with intent to keep you in the FX LOOP.

Newcomers to live sound often have problems with the Auxiliary Section of mixing desks. Often called the FX Loop, the Channel Auxiliary Sends, Master Sends and FX Returns are ways to get sound out of the desk, through a piece of gear, and back into the desk again to be mixed and balanced with the other sounds and instruments.

FX LOOP = Out of desk, into the FX, out of the FX, and back into the mixing desk.

CHANNEL AUXILIARY SENDS

Each input channel on a mixing desk usually has one or more ‘Auxiliaries’ or ‘Sends’ as a way of sending a part of its’ signal out of the desk; while the rest continues on through to the channel faders. Auxs can be used to send signal to external gear like effects gear (FX), or on to other sets of amplifiers to power the musos’ foldback. The amount sent by each channel is usually controlled by a rotary potentiometer – the type of knob that we twist to turn up or down.

Each of the individual channel sends are combined in the output section of the mixing desk to feed their Auxiliary Master control. For instance, all of the Aux 1s – on each different channel – are combined into the ‘Aux1 Master’ by special summing-amps. When used for FX, sends come in very handy when we have lots of different sounds all needing the one sort of effect. For example, the reverb unit may be fed by Aux 1 Master; the delay unit by Aux 2 Master.

POST-FADE AUX SENDS

When labelled as Echo, Effects, FX or Post – for post-fader – the auxiliary send receives its signal after the fader. As a result the amount of signal sent by the Aux remains relative to the fader level. If the fader is all the way down, no signal leaves that channel.

To put that in plain English, if we are using a Post-Fade Aux to drive an FX box and we push up the fader; the amount sent out will increase in level by the same proportion. And when we fade down, the level sent trails-off by the same amount. Sounding as if the effect is actually part of the original sound – woo-hoo!

If the signal level did not follow the channel, the effect would still be heard after the channel fades out – not cool. For example, when a delay keeps on repeating long after the vocalist stops singing!

PRE-FADER AUX SENDS

When labelled as Cue, Mon (Monitor) or Pre (Pre-fader) the auxiliary send receives its signal before the fader. As a result, the signal sent is totally independent of the channel fader. The fader position doesn’t affect the auxiliary send level, and the send will work with the fader all the way down.

Pre-fade aux sends also earn their keep in live-sound when the FOH mixing desk engineer is doing foldback from FOH, when pressed into double service by cheapskate band/tour managers. Meaning – as well as trying to pull a red hot mix of the band, the poor hard working soundie is also expected to look after the talents foldback as well!

When setting up fold back, it is crucial to be able to control the levels within these mixes totally independently from the front-of-house mix. If the FOH mix fader movements were mirrored at the channel sends, any increase in channel volume for the FOH mix would also result in these constantly changing levels being sent to the foldback. This would annoy the musos, completely alter the foldback levels, stuff the system frequency-response balance and tuning, and just about guarantee a feedback nightmare! Not happy giggers.

It is common for Pre-fade sends to also be Pre-EQ, so that all signals sent to the foldback amps remain independent from any changes in the channel EQ sent to the main FOH speaker stacks. This ensures that the only EQ applied to foldback is from the 31-Band Graphic Equalisers that we have patched-in across each send, to tune the foldback to get rid of frequencies that tend to ‘take off’ into feedback central.

FX RETURNS – WELCOME BACK TO THE MIXING DESK

The signals sent out to the FX gear must be returned to the desk, for mixing with the other sounds. On many desks there are dedicated, line-level Effects Returns. They are usually on a rotary-pot, located in the Output Section of the desk and often come with some form of basic EQ and Channel Routing functions. If we are running out of channels on our mixing desk for line level inputs – for intro tapes or MIDI gear, for example – we can always use spare FX Returns.

DANGER!

It is also common to use spare input channels for FX returns. Using a fader gives us a much finer degree of control over the level of the return; and, is heaps easier to find in a darkened gig than a rotary pot! However; it is absolutely crucial to have all Aux Sends on that channel TURNED-OFF. If the return channel’s Aux Send is left up, it will attempt to re-send the already effected signal back to the FX gear, causing an internal feedback loop. This results in the terrible howl of feedback which can destroy speakers, and, if we are monitoring on cans, take-out our ears! Be warned.

WILLY T runs Giraffe Media. Providing Words, Pics and Live-Audio Recording Services to the entertainment industry. Email for more information.

Be first to comment on this article

Write Comment
Comments are submitted for possible publication on the condition that they may be edited. Poster's IP addresses are logged.
Name:
Comment:
Code:*