That bogeyman of the live sound engineer, the man from the council, is back with new powers and new gadgets. Ben Duncan looks at recent legislation and comes up with some tips to promote peace, love, and good vibes...

When you perform on a modern festival or event stage, what is the law on sound levels? How is it applied in practice? And how do professional mixing engineers get around it?

John Newsham has been involved with the mixing for Glastonbury's main stage ever since the regular festival began in 1979. By the time sound-level restrictions were introduced in 1990, he was an FOH (Front Of House) engineer, and was well-placed to observe the effects at the four subsequent festivals.

In Newsham's experience, sound-level restrictions for events in stadia and outdoors have been based solely on off-site measurements. The local authority first get to hear of your gig (or festival, or rave, or whatever) because licensing arrangements have to be made through them, whereupon their environmental officers are alerted. These officers usually identify a few 'sensitive neighbours' - people who have made complaints on previous occasions, or otherwise the nearest housing to a venue. Days or weeks before the event, they visit the these homes and record the 'normal' sound level, ideally (but not necessarily) at the same time of day that the gig is scheduled for.

On gig day, and once the PA is set up, a well-equipped 'man from the council' responsible for monitoring levels will play his standard cassette tape of shaped (filtered) pink noise through the outfront system. If the officer is not equipped with such a tape, you may be asked to "play some music please". If so, be sure to medley a wide variety of styles. Either way, the point is to get a fair calibration of the kind of sound level metered at mix position that hits the limit at the sensitive distant monitoring location.

The sound level is also being monitored by another environmental health officer, usually connected to the mix position with a radio link. The PA level will then be raised, until the distant site reports that the maximum level decided upon has been reached. At this juncture, the sound level setting at the mix position is noted. The maximum level allowed at the 'sensitive site' varies from the 'typical level' recorded earlier, to maybe 3dB higher.

Creative accountancy

There may be some scope for negotiation here. The significance of levels at the mix position is that the audience forward of this will enjoy levels 3-15dB greater; whereas those behind will experience levels 3-15dB down on the mix position - all depending on distance, temperature, wind, humidity, crowd density, PA angling, and the lie of the land.

Even without such factors, sound levels that are allowed at the mix position are highly variable. You could be limited to less than 90dB (SPL L_eq) if, for example, sensitive housing isn't double-glazed, is on-axis to the stage, or is located just beyond the audience's back row. Or you may find you can let rip to over 100dB (SPL L_eq) if the problem residence is off-axis, further than a quarter of a mile from the mix position, or next to a busy main road - so that, in effect, 'typical' sound levels are always high.

Using highly directional PA speakers such as Turbosound's Flashlight system can also help increase allowable SPLs, by focusing sound away from the sensitive direction(s). At Crystal Palace Bowl, they've enabled high levels (about 97dB L_eq at the mix position) for gigs by Level 42 and The Cure, with houses just 100 yards away. So choosing and correctly orientating your speakers is important.

The event organisers will have to pay to hire the SPL monitoring and logging equipment that will be used by the environmental officers, who normally come equipped with nothing more sophisticated than a hand-held sound level meter. The mixing desk will also need equipping with its own reliable, high-spec SPL meter that can be read by the FOH engineer. Adequate supplies of spare batteries are essential.

Hang 'em high...

Dead ahead of the main stage is a particular problem at Glastonbury, where the festival is sensitively located close to Pilton village. The size of the audience, the amphitheatrical lie of the land, the placement of hedges and ditches, and even ley lines, all prevent the stage being simply 'swung round a bit'. Instead, the PA is nowadays hung high, with the speakers angled down. This means the high and midrange sound is mostly swallowed in the first 200 yards of audience, from which it does not bounce back.

Originally, L_eq measurements were taken at 15-minute intervals. So, if the mix engineer wanted to bring the performance in loudly, he had to arrange for the loudest part to occur at the onset of the period over which L_eq was being metered. Provided the level was pulled down well before the period was up, the fact that the music was 6dB or so above the set limit for several minutes didn't matter. This year, though, one-minute L_eqs were introduced, largely preventing any such mixing creativity.

L_eq is measured with what's known as 'A'-weighting. This means that a loud singer, riotous audience applause, or a compere hollering 'Kick out the jams' can blow a whole period; 'blowing a period' means the sound level exceeding the limits in one of the L_eq periods (of 1-20 minutes, usually).

Judicious EQ'ing can help to maximise sound levels (see Figure 1). Powerful EQ on the main PA feeds is worth having if you find that the SPL at the mix position is having to be kept down too low. The spectrum-analysing meters used by some environmental officers may be used to tune a parametric EQ or a third-octave band graphic. The answer is to make the level in the main soundfield subjectively louder, without exceeding measured SPL at the sensitive location.

One situation that can be eased quite readily is when high bass/low mids are louder outside than they would normally be indoors, where the resonance of the building's structure reduces their impact. The resonance that is amplifying the outside noise may be triggered only over a narrow band of frequencies. Once these are taken out, the overall sound level at the mixer may be able to increase by 6-10dB, with little detraction from either tonal balance or sound quality.

Dangerous driving

Overdriving the PA 'by accident' could cost your gig's promoter a fine of £1,000 or more. Yet with the best will in the world, this can happen in the heat of the moment, particularly when a series of different people are mixing. To overcome this, John Newsham recommends using a separate, high-quality compressor-limiter across the main PA feeds. The compression is set to come in before the limiting, with a ratio of about 2:1 or 3:1. The overall result is that the sound 'fattens' nicely before hard limiting sets in, and sounds louder before being squashed.

This, curiously enough, is where things start to get rather interesting. Thus far, Newsham is convinced that the sound-level limits have actually improved sound quality at Glastonbury, principally by preventing the tendency for sound levels to spiral ever upwards as the ear gets used to each increase. Equally, however, the present allowable levels are also cheating much music of impact.

At present the law is allowing the enjoyment of (say) 100,000 people and the expression of music (the UK's foremost creative export) to be restricted by the complaints of as little as one or two individuals. What is most ironic in the case of the Glastonbury festival, and elsewhere, is that the loudest, most consistent complainers are newcomers - not the local, historic inhabitants, who recognise and reap the economic benefits, and enjoy the peaceful idyll for the other 362 days - if the Royal Air Force and the roads lobby will let them, that is...