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Introduction doc available HERE

INTRODUCTION

Sound waves travel through air.

Our ears are skilfully designed so the receptors inside vibrate as the sound reaches them. The very low sounds create waves that are very slow – the peak of the waves only travel at perhaps 20 times a second. Very high sounds vibrate the waves amazingly quickly – up to 20,000 times a second.

(written as 20hz or 20khz) this is the maximum range that our ears can detect.

Microphones act like our ears and the receiver inside is caused to vibrate by the sound reaching it. That is then converted into an electrical signal – also waves, and also with a range of frequencies.

The signal produced by a microphone is very weak, whereas an electric guitar or a keyboard produce a much stronger signal.

Hence the need for a mixer desk to balance all the input sounds and make the resulting mix sound right. But the resulting mix is still a very weak signal. So it has to be fed through an amplifier to make it loud enough to send it to a loudspeaker which vibrates in a way that produces audible sound.

The mixer desk can actually do more than equalise the strength of the signal – it can change it. If an instrument or a voice is to boomy, the low frequencies can be turned down. If instead the sound is too hissy, or tinny, the high frequencies can also be adjusted.

More than that the actual nature of the sound can also be changed. For instance echo can be added, or the same signal can be copied and played with a very slight delay to make it sound as if there are two singers.

The signals arriving at the mixer desk can also be corrupted. There are lots of electrical interferences that may be picked up (switches being operated, equipment being plugged in or unplugged, even the air conditioning being turned on and off), and then when they are amplified the interference can be quite loud.

Most inputs to the system are by means of a three pin XLR plug – this feeds a balanced signal which removes the interference. (How it does this is explained at the end. Also what causes feedback howls is also explained!)

Here it is important to note that just about all inputs are plugged in at the ‘stage’ end. Here they are digitised before connecting to the mixer disk via a wi-fi or ethernet type Cat5e cable. The sockets are each assigned to an individual person’s mic, guitar, or other instrument and these should always use their own numbered input as the setup is specific to them (more on that soon).

It may be that the mic has to be shared with many different people – like the pulpit mic – but the characteristics of different people can also be stored and recalled at the touch of a button.

It is also important to understand that the loudspeakers are not there to blast everyone out of the hall like a pop concert. The whole intent of running a PA system is to provide ‘sound reinforcement’ to ensure that everyone can clearly hear what’s going on.

Now what follows is a bit technical but you can skip it if you are only going to operate the desk. Everything is saved as presets, you can’t break anything, and if all fails simply press the reset button!

Allen & Heath SQ5 mixer INPUT setup

As I say, this is technical and should only apply to those who will be setting up the system initially. But if you are interested read on. Otherwise skip to the section titled ‘Operation’

When you first look at the desk the most obvious difference is the touch screen and the fact that many of the controls relate to just one channel. This is the pathway for each individual mic, instrument etc. You can chose it’s name and colour.

There are 16 channels displayed at any one time (out of the 48) but you control which you can see.

The screen is a bit basic, but if you have a phone, laptop or tablet you can download the ‘SQ MixPad’ for free for iOS, Android, Windows and macOS. Get it from Google Play or the Apple App Store (obviously the bigger the screen on your device the better!)

Here is the same screen shown on a tablet and as you can see the display is much expanded and coloured.

Looking at the PA desk, the signal effectively comes in at the top, then travels down through the various knobs, switches and sliders (and then you’d think it comes out the bottom – but it doesn’t – we’ll get to that.) Some of the knobs etc will be referred to as ‘Keys’

The route down the board is called a channel and most are mono, some are stereo.

There is a line drawn on the desk around the touchscreen which includes many of the controls you might use to initially set up a particular channel – perhaps for a radio mic, a guitar, a vocalist, a keyboard or perhaps audio coming from a video from a laptop etc.

Before the initial setup it would be best to make a list of all possible inputs and arrange them in groups of four for convenience. Of the 16 channels available at each view, they are presented as groups of four, with each bank of faders slightly separated, and with coloured labels above. (Names and colours are your choice and groups can be of any number)

So how do we start? Press the ‘Processing’ key at the left of the bottom of the touchscreen. This then displays on the screen the results of what you are doing and also illuminates the controls that are now ‘live’.

The first thing to do is to choose the channel you wish to operate on. The screen defaults to channel 1 but you can select whatever you want. Press the ‘Sel’ key towards the top of the fader section to select that channel

It is important to always plug in the particular mic, instrument etc to the same numbered input at the ‘Stage’ end (there are 16 to choose from.)

The first key in the group labelled Preamp gain is actually the most important.

For the desk to work most efficiently each channel should start with roughly the same optimal signal strength for the desk to understand and work with. This key allows you to raise or lower the strength of the signal coming into the channel strip from your device, i.e. microphone, guitar, keyboard etc.

The resulting signal strength can be shown on the LED meter strip to the right of the touchscreen. This will help you get the right level which should generally be around 0db. (There is also a PAD control available on the touch screen.– if your input is still too powerful, this will chop off 20db to bring the signal strength down to manageable amounts.)

Again much more info is displayed on the App and for originally setting up each input source it is probably best to use the App display!

The next three keys in the group all have a switch beside them so you can choose to engage them or not.

The second key is the high pass filter (HPF). It passes through all the high frequencies but blocks the low ones. In plain English it cuts out all the bass frequencies often associated with the rumble from rough handling of microphones, some of the vibration coming up through the mic stands from the stage, a lot of the pop and the hiss, the breathy stuff from poor microphone technique. Beside it is an on/off switch to engage it or not, and the key itself controls the cut-off frequency.

It will make a lot more sense if at this point you watch a short training video (3 minutes) about the HPF which is available HERE

The third key – Gate – we won’t be using. But the Compression key we will look at after we have looked at Graphic equalisation.

Below this section is a rotary ‘Pan’ key to lower or increase the real or apparent signal ultimately going to the left or right loudspeaker. We won’t use that either.

So lets look at the keys on the right of the touchscreen, and here we will concentrate on those labelled 5. This is the graphic equalisation section. This allows you to adjust specific frequencies that may be causing you problems. He buttons on the right select HF – High Frequencies, HM – High to Mid, LM – Low to Mid, and LF – Low Frequencies. Once you have selected the range you can use the rotaries to pick a particular frequency within that range, widen or narrow the range either side of that frequency, and choose to raise or lower the signal strength just there using the Gain Rotary.

If the microphone user occasionally speaks VERY LOUDLY the Compression rotary in group 4 on the other side of the touchscreen will be invaluable!

Here it will make a lot more sense to watch the next training video (10 minutes) HERE.

So we’ve more or less got all the inputs balanced ready for the mixer desk to start its work.

Allen & Heath SQ5 mixer OUTPUT setup

Perhaps now would be a sensible time to allocate a name and number to each channel. Press the 'Select' button immediately below the touchscreen. The touchscreen display changes and you then choose a tab labelled 'Surface'

Now touch the 'Strip assign' tab and enter what you will.

There is also another opportunity to adjust the input signal and that involves the built in ‘Effects’ known colloquially as ‘FX’ (cos that sounds the same!) This is the group of keys labelled 8 on the far right of the touchscreen.

I expect that only Darren will want to get involved in that so apart from saying press the FX button under the touchscreen I’ll say no more!

Before leaving the whole input section you will notice that there are 8 ‘soft keys’. These keys can be assigned by you, using the software, via the Setup screen to provide shortcut buttons to any function you choose.

Of course having set up and adjusted each input you will want to get the ‘mix’ level sounding right before sending the combined sound to the speakers . That’s where the main sliders come in.

I said earlier that the signal comes in the top and travels down the board. Now, instead of coming out the bottom perhaps we should think of it coming out the right hand side!

Immediately, of course, there is an exception. The whole aim of the mixer is to provide sound from the loudspeakers and it is assumed that just about all the inputs will be routed to the L/R MAIN MIX MASTER output (Yes the documentation swaps between all those terms!) with its own slider to control the final sound level (as the hall fills up with people, sound is absorbed and the volume may need adjusting).

But apart from that, on the right hand side of the desk there are 12 buttons, grouped in 3 sets of 4.

It is presumed that mixes 1-4 will be used as Aux outputs (and they will light up blue if selected) but all mixes could be Aux or Group – more on that in a mo.

What is an Aux output? Beside the main speakers we need to send auxiliary sound to the people listening on Zoom, so a separate mix will be directed to the Laptop’s USB socket.

We currently send a sound signal to the Hall’s hearing aid loop system (but I doubt it’s current usefulness).

Mainly the Aux sends will be used by the musicians for their in-ear foldback. These Aux sends will be directed to specific numbered output XLRs on the Stage Box where they can plug in their individual amplifiers. Here they can decide which inputs and at what levels they individually want.

When you select a mix button the faders are tied to the mix – so press the ‘Sel’ button at the top of any appropriate channel strips you wish to include and adjust the channel output levels to suit. While you are doing this the Master output fader will control the mix output level of the combined channels in the mix. These adjustments don’t disturb other adjustments you have already made for those channels.

All this is displayed on the touchscreen by pressing the ‘Routing’ button under the screen – here again it may be clearer on the laptop.

On the routing display, we can see an overview of all send levels and assigned groups for 8 channels at a time (You can drag the display sideways to show other channels).

Touching any of the routing sections on a channel shows assignments and levels in greater detail, and you are able to switch channels in and out of mixes completely.

But what are groups?

Before we talk about that we need to Explain some more terms. First DCA ‘Digitally Controlled Amplifiers – simply what we have been doing to adjust the input signal for each channel. Secondly PAFL ‘Pre and post Fade Listen’. This refers to what you want to hear on your headphones – effectively you can listen at any point to any channel or mix. And lastly MUTE. This is very powerful – you can instantly mute whatever you choose!

Groups allow you to group together any channels so you can deal with them at the same time. The best example is a mute group. Here you can mute perhaps all radio mics, or instruments, or whatever you fancy. If you are getting speaker howl, to be able to instantly mute some groups could be very useful.

Or a DCA group could be a set of inputs that you would like to listen to on your headphones to balance them – perhaps a group of singers for Christmas.

That’s where PAFL comes in. Some things you want to listen to here exactly as it arrived at the mixer – ‘Pre Fade’. Other things: after all equalisation cuts, boosts, and faders have been applied – ‘Post Fade’ (Actually if you are really excited you can listen to any point in between as well).

At this point there is a bit of an overlap between ‘Setting up’ and ‘Operation’ so we’ll label the rest

OPERATION

Once the desk has been set up, all settings can be saved. This means that at any time you can press the reset button and all saved settings will be returned. (Very dramatic if you have moved sliders, as they will ping up or down the desk to their original settings!)

Sets of settings can be saved as ‘shows’ and within that ‘scenes’. For us that could be ‘Normal Sunday’, or ‘Christmas’ as a show, and ‘Main radio mic’, ‘Pulpit mic’, ‘PowerPoint video’, ‘musicians’ etc as scenes.

Each of these can be recalled at the touch of a button, only the sliders might then need slight adjustment.

Traditionally many different voices could use the pulpit mic so you may need a group of different settings for ‘Loud male’ to ‘Quiet child’ etc . You would then be able to choose suitable basic settings which would be appropriate for whoever is speaking.

Much of the setup will have been planned beforehand so actual operation should be very simple (!!)

Best thing is to come on the training Saturday and have a play yourself.

FEEDBACK HOWL

We have all heard it so what is it? And what causes it?

Generally sound enters a microphone,

is amplified,

and comes out of a loudspeaker louder.

But some of the sound can find its way back into the microphone and start amplifying it again

and again

and again

until the howl is very loud!

Actually even guitar strings can act as a microphone!

How to avoid feedback?

Always ‘Mute’ any instruments or microphones unless they are needed.

Never point a loudspeaker at a microphone or instrument. Remember sound comes out of a speaker in a cone shape so keep them well apart.

Don’t casually walk in front of a loudspeaker with a live microphone!

BALANCED SIGNALS

Imagine a sound wave

Now using clever electronics reverse it so all the plusses become minuses.

Now send both signals (plus and minus) down a pair of wires with the third wire acting as the ‘Earth’. That is a balanced signal.

When it reaches its destination the electronics changes the minus to plus and the signals are added together to make a stronger signal.

Now imagine at some point an electric ‘spike ‘ attacks the signal. You can consider the spike is always ‘plus’ as it attacks the cable.

Now when arriving at the signal’s destination, the polarities are reversed and the two signals are added together as before. But now the second ‘plus’ spike becomes a minus ‘spike’ and exactly cancels out the ‘plus’ spike’ – removing it completely!