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Headphone level control – monitoring versus limiting

Technology has allowed higher and higher sound levels to be produced at better and better quality over the past 20 years but more recently there has been a realisation of what this can do to people's hearing. The European Commission acted on this in 2003 by issuing a Directive to harmonise noise control legislation across Europe, which led employers in broadcasting, live music and industry to consider how to protect both staff and the public. In broadcasting, limiter circuits on headphones have been a first line of defence but, as Kevin Hilton reports, a new approach is being taken for location filming.

 Wearing headphones for long periods of time is not the most pleasant of experiences but in TV and radio it is part of the job. And people do get used to it, just as they get used to the volume levels coming through the cans. Which is where the trouble can start. Andy Benjamin, DV Mentor of DV Solutions, the BBC’s internal hire and support unit, realised this and set out to find a way of making camera operators and sound recordists aware of potentially dangerous levels without compromising audio quality. Benjamin’s idea was for a way of monitoring volume over a period of time, with pre-recorded voice warnings given if someone had been listening at too high a level for too long. He took his basic concept to Glensound Electronics, which designs and manufactures headphone amps and limiters, alongside its intercom, commentary and mixer-codec products. The result of this collaboration, the GS-HL005 headphone exposure meter and attenuator (pictured), took two years to develop and was due to be available this month. The unit is the latest attempt to give broadcasters equipment that allows them to comply with the revised Control of Noise at Work Regulations, introduced by the UK government during 2005 in response to the EC Directive. The Regulations became law for most industries in Britain during 2006 and were extended to music and other entertainment in April 2008. Broadcasters have always found headphones difficult to police; mythology tells horror stories of old-school DJs like the late Tommy Vance, who had a pre-amp built into his headphone circuit for terrifyingly high volumes, which he said he needed for pitching his voice. Even in less extreme examples operations staff remember the days of ten to 15 years ago when maximum headphone levels were around 96dB. Under the new legislation this has been reduced to approximately 85dB but there are still potential dangers; presenters or operators monitoring for very long periods or pushing the levels as much as they can. One way to solve this problem is limiting the overall output. Several limiters are available; Glensound produces the GSXH2 and GS1U-044 stand-alone compressor boxes, which were developed with the former Capital Radio group. Canford offers a range of headphones with either integrated limiting circuits or limiters cut into the lead. These include the Sennheiser HD480, beyerdynamic DT100/109 and Canford’s own DMH205/285, all of which feature limiters based on technology licensed from the BBC, whose engineers designed it in the 1980s. Benjamin comments that for professional audio reasons such passive limiters are not ideal: “The compression and distortion rule them out for quality monitoring and they also simply reduce level by around 6db, making the fitting pointless on some of our equipment.” BBC News Technology Operations is hoping to standardise the headphones used in the BBC newsroom, although Huw Davies, a trouble-shooter with BBC Future Media and Technology, says this is difficult because “what the manufacturers are producing doesn’t really fit our requirements for headphones that are suitable for consistent use, with comfort and durability being a factor”. He adds that the main challenge is finding a headphone that is suitable for newsroom staff and can have audio limiting built into each can rather than in-line, otherwise there is the potential for point of failure when staff walk away from a desk still wearing their headphones. The chief executive of Canford, Chas Kennedy, agrees that limiters do affect audio quality but does not see this as necessarily a problem. “In most cases headphones are being used to monitor in-coming lines or for editing programme material, not for quality control,” he explains. “Production staff work in open plan offices with a cacophony going on in the background, so some control is needed to prevent them from listening at too high a volume.” Benjamin responds by suggesting that headphones with good noise isolation should be used instead of increasing listening levels to the point where a limiter is needed. The best approach, he feels, is measuring exposure to audio levels and making people aware of volume and how long they’ve been listening. BBC Health and Safety passed this philosophy as acceptable, after much discussion. There is also an economic expedient. “We use the Sennheiser HD25 at DV Solutions as we feel it’s the best headphone for location work,” Benjamin explains. “We’ve already got around 300 pairs and from the point of view of suitability and quality we don’t want to change them. Adding a passive limiter would ruin the sound quality, create a reliability problem and, of course, add cost.” The GS-HL005 is a small device, which Benjamin describes as looking like a radio mic transmitter. It is powered by a rechargeable lithium ion battery, a USB connector or a power tap from the camcorder or other host equipment. It sits between the sound source, a camcorder in this case, and the headphones and is carried on a belt clip or in a pocket, with a locking clamp fitted so it cannot be disconnected from the headphones. The unit has no effect on audio quality but passes the signal through intact. The operator will hear just three spoken instructions and a warning if maximum levels or exposure time are about to be exceeded. “If someone stays within the permissible the operator will typically get just the one or two messages,” says Benjamin. “One huge advantage of this unit is that short periods of higher levels are possible, such as you might need in an environment with high background noise level, for a spot check or fault finding. This ‘boost’ is available at the tap of a button on the unit. They are automatically cancelled after 30 minutes.” If the maximum working period is reached the user is given the choice of stopping work or overriding the system to carry on monitoring. The decision made is stored with the time and date and can be downloaded with a full listening history into a PC. This log can be inspected by managers. The Noise at Work Regulations are designed to protect staff but also employers, who could be liable for anyone suffering hearing damage. Benjamin acknowledges that not everyone will like using the device, at least initially, but says it is like wearing a hard hat on building site: “It’s uncomfortable but ultimately everyone knows it’s a good thing.” As well as location recording the GS-HL0005 is seen as suitable for other broadcast applications, including presentation talkback and radio. To make an automated incarnation of health and safety rules more acceptable Benjamin is hoping to use the voices of celebrities in music or broadcasting who have suffered hearing loss to explain why keeping the level down is vital. These will be short messages available as options on the unit. George Martin is said to be interested but Benjamin would like to involve others. “It will help sell the concept of using the system,” he says, “and get across the importance of protecting yourself from hearing damage.”