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Perception of loudness is a complicated subject. Every person will perceive loudness differently, as everyone’s ears are different. In fact, everyone’s ears have a slightly different frequency response.

This is why, in sound engineering circles, there is a need to quantify sound pressure levels to define what is loud, and what is quiet. Or perhaps that should be; what is too loud and what is too quiet. The unit of measurement is the dB SPL (decibel). There are also more accurate measurements of loudness called phons, and subjective loudness, called sones, but these are rarely used and are outside the scope of this course!

For convenience we normally measure dB SPL from the mix position, but it can be useful to measure from other areas such as the front row and the stage.

For those new to dB SPL here is an idea of how different sounds compare in level:-

To make things more complicated, perceived loudness varies with frequency – a low frequency sound of the same measured intensity will sound quieter than a mid-range frequency sound. The dB SPL (A) weighted scale is designed to help compensate for this.

Some KEY FACTS to remember about dB SPL:

• A 3dB increase is doubling the acoustic energy… and requires double the power (e.g. 1000W amp rather that 500W) BUT the perceived volume increase is much less – around 30%. Subjectively a ‘noticeable’ volume increase.
• Doubling the distance from a loud speaker, in normal circumstances, reduces the sound by 6 dB SPL – approximately a 60% perceived volume reduction. The same applies, critically, to moving away from a microphone.
• A 10 dB SPL increase in volume is regarded by most people as a ‘doubling’ in volume. Approximately 10 times the power is required to ‘double’ the volume. (e.g. 5,000W amp rather than a 500W amp!)
• High sound pressure levels WILL damage your ears. Most at risk are professional musicians (especially drummers), sound engineers (both live and studio), and nightclubers. My hearing has been permanently damaged due to loud guitar amplifiers and loud car stereo systems.

Ways that dB SPL can be useful to you:

• Measure and keep tabs on your volume levels, both on stage and FOH.
• Add weight to your arguments with the audience, management, and performers.
• Greater understanding of speaker and microphone placement.
• Understanding how to use a compressor and why.
• Understand and use the markings on the faders – they are there to help you!
• Understand how to protect your hearing.

Running a successful sound check is mostly about proper preparation. If you have a similar band and a similar set-up in the same venue each week, you are fortunate, you have all the time in the world!

A sound check is 80% getting the stage sound right for the band, and 20% getting it right for the front of house. Front of house mixing is much quicker and easier, as you only have one mix and only your own ears to please (for now), but the band could have 4 or more mixes and all kinds of preferences.

How to set-up a suitable gain structure:

• Make sure your amps are all set on max (unless some have to be backed off to achieve a good mix of levels on the balcony or wherever)
• Play a CD to get an idea of the overall system gain and where to initially set the main output faders.
• Plug in a mic at the desk.
• Set the channel EQ flat.
• Push in the PFL button on the desk.
• Shout in the mic at close range whist adjusting the gain to just below peak reading on the desk PFL meters (normally the main output meter doubles as the PFL/ AFL meter)
• Set up a compressor or two on your key vocal channels if possible. Double check the gain levels.
• Take note of the position of the gain knob. (Have a chart handing to record your settings if possible).

Setting initial EQ:

• Bring up the FOH and listen to the sound of the mic. Normally, low cut (HPF) and a little less bass is required on a vocal mic, especially in a band situation.
• Set the gain and EQ in a similar position for the other similar mics.
• Put some signal to FOH and monitors. A prior knowledge of which mics need to be in which monitors certainly helps.

Setting up initial monitor levels:

• Take note of the AUX knob position required to achieve a certain volume on stage. Playing a CD can sometimes help with this as well.
• Wind up the AUX until feedback starts. Take note of this position.
• Back the AUX control off… Now try the FACE / FLAT HAND / CUPPED HAND test on all the mics, to check for ringing. Adjust the AUX sends if required.
• Bring up the FOH until feedback starts. Take note of this as well.
• Now that you know how much ‘headroom’ you have to play with, back off the mic levels at least to 10dB before feedback – preferably more.

Sound checking with the musicians:

• Hopfully, you've agreed a time for the sound check in advance with the organisers. If not, make sure you agree a time with the musicians, when they arrive. Make sure you leave the musicians enough time to set up their intruments and do their own 'checks'.
• Our advice would be to start with the key channels first, and spend care on these... lead vocals, lead intruments. The exception of course if some musicians are not ready – just sound check those that are. Don't make the mistake of spending ages on the kick drum and then run short of time to check the lead vocals at the end.
• Ask each performer to play their instrument (or sing) one at a time.
• Quickly check the gain level is within your expectations, and adjust / PAD as necessary. In the case of your vocal mics, you’ll probably want to leave the gain where you set it earlier. Also make sure you have any compression or inserts working at this point. Large multi-mic set-ups can become difficult to manage if mics are being swapped about if the gain controls are all set differently.
• Make sure you have some sound going into the monitor and the FOH. Stop the performer and ask if they are happy with the monitor sound. If you are lucky, they will ask you to turn the monitors down! Otherwise, they may want all manor of EQ and reverb… in all cases, use the controls sparingly. Remember the artists ears will adjust to the sound of the monitors / PA / room after a short while.
• Repeat the procedure until the performer is happy. And you are happy. If in doubt, leave the EQ flat – as long as the performer is happy, you can always tweak (a little!) later.
• During the above process you may want to put a little of the sound of that musician into the other monitors. The other musicians may well be listening.
• When you have checked all the performers, ask them to play the chorus of a song they all know and play in. Ask them to listen to the monitors during the song. When they have finished, they may ask you for more of this or that in the monitor – That’s great, because how are you to know that Geoff on the drums needs to hear more of the lead banjo to stay in time? If nobody says much, walk up to the stage and engage with the band. Ask them if they are happy with the monitor mix. Ask them if they can hear each other clearly. This type of communication is pretty much the only way to achieve a good monitor mix.
• Another thing that helps is to wonder around the stage whist the band are playing, and listen to each of the monitors. It’s often surprising how much different things can sound on stage. And if you are controlling the stage mix, it’s important for you to know.

We get asked this all the time, and we're afraid that there is no very short answer (other than “turn it down!”). However, there are steps that can be taken to greatly reduce the risk of feedback. Reduce the risk almost to zero in some circumstances.

• Reduce on stage volumes where possible - then you can reduce monitor gain and hence reduce the possibility of feedback. Prime culprits here are on stage bass guitar amps, and drums... drums being more of a challange to 'turn down'!
• Encourage vocalist to sing really close up to the mic. Not all singers are used to, or like this technique, but from a monitor engineers point of view it works best! A good singer can still pull the mic away a bit for louder syables, words or sections. This tip is especially hand for vocalists that are asking for more in the monitors than you can give them without feedback.
• Eliminate simple causes of feedback – for example a guitar or bass left plugged in, turned up and on a stand. Inexperienced musicians are prone to doing this and need to be educated!
• Make sure your FOH speakers are positioned not to bleed into the microphones.
• Be aware of the pickup pattern of your microphones, and use this to your advantage. Most mics are cardiod, and so are pretty directional. Make sure they are not pointing at monitors or front of house speakers.
• Don’t put unnecessary mics such as the drum overhead into the monitor system.
• Don't use more mics on stage than nessasary. Every time you double the number of mics on stage, you reduce the gain before feedback by 3dB (the system will start to feed back at a perceieved volume about 30% lower than before).
• Use good quality microphones. If you’ve ever used a really cheap mic, you will know how prone they are to feedback and handling noise. Having said this, many people won't find much difference between an £80 microphone and a £350 microphone. Just avoid the cheapo £20 mics and you should be OK.
• Use good quality monitor speakers. Many venues try to save money and buy cheap monitors for the band – this is a shortcut to feedback problems, and a poor stage sound.
• Use good quality FOH speakers. Poor quality FOH speakers can also give feedback problems due to comb filtering and un-even frequency response.
• Hearing loop systems can cause feedback, especially into electric guitar pickups. Solve the problem by removing the guitar from the loop mix, or reducing the loop mix level.
• Follow a standard sound-check procedure (for an example, read running a soundcheck) and make sure to do the FACE / FLAT HAND / CUPPED HAND test, with all the mics ON, both in the monitors and FOH.
• Listen to the feedback and identify the frequency. This can be done with skill – or when an audience is not there, you can ‘sweep’ the mid band EQ and ‘find’ the offending frequency. Cut the frequency by 3dB and the feedback problem will reduce. More cut can be used in some cases, but will of course start to influence the sound of the mic. Low frequency feedback (for example from a tie clip mic), can be reduced by cutting the bass. LF feedback from a kick drum or toms is normally countered using a gate.
• Use a graphic EQ on either the FOH or relevant monitor mix to cut the offending frequency. Some engineers ‘ring out’ a monitor or FOH rig prior to a show. This can result in up to 6dB more gain before feedback. However, the monitors can end up sounding rather dull, as one normally ends up with quite a bit of upper mid-range cut on the EQ (The bands on a normal EQ are not really narrow enough, and end up cutting more frequencies than are required).
• Use a feedback destroyer. In some ways a last resort… the cheaper f/b destroyers such as Behringer can have problems with noise levels. Sabine make better but more expensive models. They use very fine notch filters to cut feedback frequencies and need the system to be ‘rung out’ prior to use in order to work at their best. They should give about another 6dB gain before feedback, without the side effects of graphic EQ or channel EQ.

Compression is an essential tool in modern sound engineering. Most commercial recordings will have compression on just about every instrument. In the world of live sound, many amateurs do not correctly understand the best use for compression.

Compression should be used in the first instance to help achieve a sound without harsh or unexpected peaks that cut though and ‘grate’ on ones ears. The human ear is actually more sensitive to these mid-range frequencies. The main culprit here are vocals. This is because vocals have a lot of mid-range frequency content, and because singers (even good singers) often unintentionally vary the distance from their mouth to the microphone, effectively giving their voice even greater dynamic range.

Adding compression limits the dynamic range, evens out the small variation in microphone position, and provides a smoother sound for the audience. You can achieve a similar effect by ‘riding’ the fader on the vocals and listening, but it’s pretty hard work, and the singer can catch you out.

Suggested settings for vocal compression:

• Ratio 3.5:1
• Adjust threshold so the gain reduction is showing 3-9 dB during singing.
• Adjust the limiter so it cuts in only on the peaks, if at all.

Suggested settings for tie clip mic:

• Ratio 8:1
• Adjust threshold so the gain reduction is showing 3dB or less during talking
• Adjust the limiter so it cuts in when the gain reduction gets to 9dB (un-clip the mic and move it closer to your mouth to do this)

Suggested settings for bass guitar, or electric guitar:

• Ratio 2.5:1
• Adjust threshold so the gain reduction is showing 3-6dB during playing

Suggested settings for acoustic guitar:

• Ratio 4:1
• Adjust threshold so the gain reduction is showing 3-6dB during playing
• Set the limiter to cut in when the gain reduction gets to 9dB

It’s important to remember that using a compressor on an insert will affect the signal sent to the monitors as well. Too much vocal compression may be annoying for an experienced vocalist who expects the monitor to get louder as they approach the mic. Although, in the case of an experienced vocalist, less compression (lower ratio) is normally needed to reign in the sound!

Use of the attack and release controls can change the way the compression behaves. It takes a while to become familiar with the effect of the controls, and with what works and what doesn’t. In most cases, a fairly fast attack and a medium or slow release is the way to go. We would suggest you leave your compressor set on auto if it has this feature, and if not, leave the controls at 12 o’clock!!

Compressors can be used for a variety of other applications, even across a whole mix. This can have un predictable effects – in general it’s best to restrict the use of compression to a few key channels, unless you really know what you’re doing!