Live Sound

The role of an audio engineer is no longer exclusive to the recording studio. The skill set of a modern engineer extends to video, radio, graphics and many more. One of the key growth areas for ? nding employment opportunities in the sector, is that of live sound engineering. The theory of live sound is one which combines the two things present in most musical engineering, technical ability and intuition.

Each one is as important as the other, a live sound engineer has to be able to be a master of both their equipment/set up, and of the live sound mix which can differ vastly from an in studio mix, applying different techniques and principles. At the core of the live sound set up are 2 things, the mixing desk and the speaker system/rig. The applications of the mixing desk in a live situation show many differences compared to its use in a studio, even in the earliest stages such as choosing the type of desk!

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For instance, in most instances a live engineer would lean towards using a digital mixing desk as apposed to the generally more desired analogue desk in the studio situation. One of the prime reasons for this is that a digital desk can contain audio processing equipment within its interface, such as gating and compression. These are available at the touch of a button, as apposed to the outboard equipment used in a studio. This feature can help save valuable time when mixing a live event, this example shows one of many advantages of using a digital desk for live. Live in Cotgrave… ’ An image capturing the digital yamaha desk, courtesy of Merlin PA’s live sound engineers. [1] As well as there being 2 types of mixing desks, in the live sound sector there are 2 main uses for a desk. The most obvious is for bringing all the signals to the main speakers and creating the mix, this is known as front of house (FOH). The other is for stage monitoring, creating a mix or separate mixes for the musicians particular taste(s). At bigger events, often there re 2 desks in play, one for the front of house and one speci? cally for the on stage monitoring. EM LIVE LOUNGE FOH mixers Front of house mixers usually come with a set number of input channels; 12, 16, 24, 32, 40 and 48 channels are what is usually found, specialized mixers used for bigger rigs can be sizably larger. The use of this large number of channels can range from the close micing of a drum kit and guitar amps, to the music used between acts and pre recorded tracks used in a set.

Another use for having so many channels is if a show with many acts on the bill is taking place, and bands settings need to be set. However, with the advancement of digital desks with recall systems and ? ying fades, needing to manually save a live mix has almost become a thing of the past. The features on a mixing console vary with the expense of the desk, but the regular features include: – Input sockets (typically XLRs for mic and DI signals) – Phantom power, phase inversion (important for sorting out phase issues in a live mix, especially is the mix contains identical signals, e. . the mix and line signals from a bass guitar) – Pad (reduces the signal by a set amount, typically -10db, this is useful for controlling over loud signals, such as a over eager guitarists amp) – Gain control (to set each signal at a sensible level before mixing) – Equalisation (this comes on all desks, both live and studio based, however in live the tendency is to use an external graphic Eq in order to meticulously notch out those problem frequencies) – High and Low pass ? ters – Panning – Auxiliary send (used for effects and vastly used later for the monitor desks One feature of most, if not all desks, that is utilised greatly in live sound are the sub group faders. This means that once a sub mix (e. g. the drum kit) is mixed, the faders can be assigned to a sub group with a singular fader to bring the whole mixed up or down as one. This is a great time saving device when mixing on your feet!

Also on more sophisticated desks, other groups such as solo and mute groups are present so certain parts can be muted together if needs be. ELECTRIC MAYHEM: LIVE LOUNGE Pictures from group E1’s live lounge session recording … .1 – Setting up the drums . 2 – Crate guitar amp FOH & Monitor mixing desks Monitor Mixes. In a smaller set up, the monitor mixes are usually done from using the Aux sends. This will work but there are not usually enough of these to create a .3 – Neve VR analogue ! mixing desk [2] “THE MONITOR SET UP IS MORE PRONE TO FEEDBACK.. .. so several types of eq may be used” ‘live sound manual’ comprehensive monitor mix, this is generally because if there are 4 aux’s on a small desk, 3 and 4 will be dedicated to using effects, and therefore will be set as ‘post-fader’. Whilst there are many large scale gigs around, so the majority of mixers manufactured and sold are of a budget and mid ranged level. Therefore dedicated monitor desks are quite rare. Because the application of these desks are different, they obviously have difference features.

One thing to note is that they contain many auxiliary sends, enough to house one mix for musician, there are also many groups, usually ranging from 8 to 24. Extra out board equipment – a multi-band compressor in action each As well as these advanced features, monitor mixes also contain many controls identical so the FOH desks, thought they can still often be used in a different manner. These features include: Phantom power, PFL/AFL, FX sends and returns (used for effects such as ‘vanity’ reverb), and of course, Eq. On monitor set ups, Eq are used more because it is more prone to feedback, being closer to the microphones on stage.

Power amps These are essential to a live sound set up, they work as power converters as the signals in the PA up to the point of the power amps are too ‘lightweight’ in current and voltage for the speaker system to recognize and the sound to be loud enough for a gig. They work the same way as pre-amps in the actual mixing desk. The way a power amp works is that the currents signal ‘swing’ increased to raise it to the optimum level for the speakers, and ampli? ers voltage swing can be elevated by between 10 and 50 times (compared to the line levels which can be as low as 2 volts).

Power amps have many classes (A through to H) and generally come with balanced XLR inputs. Signal & Effects Processing Processes to effect the live sound signals come both internally in the mixing desk and also as outboard equipment. This is usually referred as the FX rack. These effects can used to control, clean up, blend and add to a live mix, including compression, gating, reverbs, equalisation and delay, these processors are connected to the desk using auxiliary sends or channel inserts… [3] “Gating can clean up the FOH sound, stopping unnecessary spil . ” ‘live sound manual’ EQ – This comes in different, versatile forms. From the simple 3-band eq’s found on budget mixing desks with hi, mid and low eq pots, to the more elaborate forms such as graphic and parametric. Graphic equalisation is generally found when using monitors, this is because, due to the fact that monitors are near to, and have so many mics pointing towards them, the eq needs to be very advanced in order to notch out those problem frequen- AN EXAMPLE OF MERLIN PA’S SET-UP IN ACTION! enough to give quick access. cies.

It is called a graphic eq because the notches used give u an accurate representation of the curve that is formed when changing the frequencies, they generally have 28 to 31 bands. GEQs are usually outboard equipment, as they need to be big Parametric equalisation is the most powerful form of Eq. This is because not only will it allow an engineer to notch out those pesky problem frequencies, but because it contains a ‘Q’ control, this helps control the spread of a frequency peak, this means that one is able to precisely effect the narrowest of areas if needs be.

Now that most desks used in live are digital, any engineers now use the built-in equalisation features that come with the more high end models. These are usually coupled with a digital representation of the Eq. The advantages of using digital as apposed to G and PEQs are that the eq’s can in theory be perfectly matched channel by channel, and these settings can be saved in an internal system. Also, in higher end systems, one is able to see a visual of the sound coming through the channel, therefore seeing which problem frequencies to notch out and how they are being affected in real time.

Effects – such as reverb and delay can be found as both internal, and outboard equipment. These are essential to create a cohesive mix and comes even in most budget mixers big enough to put on a gig. It can add different kinds of space to a mix, pushing instruments back and forward in a mix, and generally blending the sounds together as a whole, especially in outdoor events, where there is nothing for the sound to bounce off. Reverb is generally coupled with some kind of Eq on an Aux send channel, this can help to brighten the sound of a room arti? cially.

Delay, or echo, has been used in different forms in live sound since rock n roll slap-back in the mid 50s. It has since been used on almost everything to create its own sense of space and ambience. Most delays, be it outboard or internal, runs once again through an aux send, and comes with features like delay time, decay and usually a tap tempo button to adjust the speed. Gates & compressors – these are essential in a live sound set up. Gates help to cut out spill on ‘single hit’ channels such as the snare and sometimes backing vocals, this helps cutout spill which could otherwise make a mix seem ‘muddy’.

They work by setting a volume threshold at which the sound will be let through when reached. Gates can come in outboard or onboard formats, and once again can be useful as onboard equipment because visual representation can be a feature on higher end desks. A more advanced feature on some gates is ‘side-chain’, this means the gate can be control by things such as Eq, so instead of just a volume threshold, the gate can be worked by a certain frequency (e. g. for feedback). [4] Compressors are also very important pieces of equipment in a live sound set up.

It is essential for controlling sounds, tightening them up and making them more ‘punchy’. Compression can also be used to make sounds louder, bringing up the quieter parts of the sound and raising it as a whole to make it more useable in a mix (this could be useful on quieter instruments such as ? utes). Another example of this type of compression being useful is in vocals, most vocalist, however experienced, have unexpected jumps of volume in their singing, so compression is pretty much the only way to deal with this. Compressors work in a similar way to gates.

They have a threshold which sets the level above which the compression takes effect. The ratio tells the compressor how abruptly it will work (if a compressor is above around 15:1 it becomes a limiter), and it features attack and release functions, to dictate how fast the compressor will work and how quickly it will cease to have an effect. Also, more advanced compressors again feature sidechain functions. Microphones There are many kinds of microphones used in audio engineering. In live, those mics which are robust and durable are generally favoured for obvious reasons.

The type of microphones that are used in live work are mostly dynamic mics. The two main reasons for this is because they posses the durability previously mentioned (the other main type, condenser mics, are quite delicate and can be damaged easily if for instance they are used on a tour) and because they have a very directional quality, perfect for close micing which is used for the most part in live as the engineer is usually dealing with micing guitar amps, kick/snare drums and of course vocals. Condenser mics are used, but only when needs be, such as with drum overhead micing, where a bigger audio spread is needed.

Mics with switchable polar patterns are also desirable in live sound work. An example of this is using a ? gure of 8 pattern, if two vocalists were using the same microphone, this pattern is equally sensitive at the front and back of the mic. “A mics response pattern changes as soon as someone picks it up, even if it’s designed to be handheld. . ” ‘live sound manual’ Speaker Systems The speakers are the face of a PA system, they are ? nal part in puzzle that is live sound. This means they have to be of a high quality, carefully matched to the power amps to create the best sound for the audience.

A speaker can be broken down into individual parts. The cabinet, which encloses the speaker as a whole, this can be shaped to emit the sound in a certain ways, usually to put out the best sound of course! These cabs, like the microphones used in live are built very solidly. This shows a vast difference to their studio equivalents, which are often catered much more towards being aesthetically pleasing or compact. Inside this casing lies the heart of the speaker, usually referred to as the drive-unit. [5]

A drive unit, or driver, is a transducer like that found in a microphone, but with the difference that it works in reverse, this means it takes electrical currents and transforms it into sound waves. Like in microphones, the most commonly used transducer using moving coil principles (just like dynamic mics! ), this is again because they are the most reliable and economic. The diaphragm in a speaker is what the coil connects to, it used usually made from a paper pulp and vibrates when the signal is passed through it. Most speakers contain two of these diaphragms, both held lightly in place by a metal chassis.

One for bass frequencies (which takes its name from this ‘chassis’) and another for the higher range, referred to as ‘tweeters’, these tweeters require a light but ? rmer cone. Basically, bass frequencies equals more vibration, which equals a bigger cone needed to cope with this. The driver units are the real ‘worker’ parts of the PA system. For most systems, a singular driver unit can cover a chunk of audible range, around 3 octaves worth. Most high quality sound systems use multiple drivers to cover the 10 to 12 octaves that are present in human hearing, these are divided up by means of a ‘crossover’. FOR MANY ARTISTS & AUDIENCE MEMBERS, THE SPEAKER CABS ARE THE PA! ” ‘live sound manual’ Common techniques & practices Voicing the PA – Before the band or act arrives to soundcheck, a common practice is to make sure the PA sound good on its own, this is known as ‘voicing’ the PA. This is generally done by playing a song (it helps if you know it well! ) and blast it out through the speakers to make sure is sounds correct. This is a good way of sorting out the FOH sound even before the audio signals are put in place, and can be used to identify problem frequencies in the room.

This way, when the band is in place, any problems that are occurring are more likely to be a problem with the sound behind the PA, such as mic positions. Pinking the room – Pinking is the process in which live sound engineers blast ‘pink noise’ through the PA system at a high volume level. Whilst the well known ‘white noise’ is a concoction of every frequency, its pink equivalent is a blast of random frequencies. This helps to identify problem frequencies in the pre-sound check. RT60 management – RT60 is a reference to how long the reverb takes to decay below 60 decibels.

For RT60 management in live sound, a loud noise is produced and the RT60 time calculated. This helps the engineers ? gure out how much natural reverb is present in the room, and therefore how much arti? cial reverb to add later. Inverse square law – Testing this process is much more relevant when mixing at bigger venues. The inverse square law states that a quantities size is directly proportional to the distance it has travelled. This helps to decipher how loud the PA should be, depending on how far the sound has to travel. Mic placement – Mic placement is important as a practice, it helps to improve the mix and save time!

Many live engineers spend ours Eq’ing channels during soundcheck, when the simplest solution could be to spend more time on getting the best direct sound with placing the mic on the sound source. Avoiding monitor feedback – As mentioned earlier, because the on stage monitors are very near to, or have microphones pointing at them regularly, there is a tendency for feedback to occur. Therefore careful Eq using a graphic or ideally a parametric eq, to identify the problem frequencies in the monitor mix before working on the FOH sound. [6]

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