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WIRELESS MICROPHONESby David Fox Why digital doesn't represent the same breakthrough for wireless microphones as it has done for so much other technology. Plus -Three users of radio microphone systems tell us what they use and what they feel is important when considering what to buy. |
Digital Danger For Radio Microphones
Most broadcast technologies have gone digital over the last decade, and have benefited as a result. One analogue hold-out is the radio microphone. It is under pressure to go digital, because regulators believe that will free up spectrum, but this is one area where digital isn't necessarily better. The spectrum available for radio microphones is already something of a nightmare for European users, as what is available varies from country to country, and even within regions. It usually uses spare spectrum within the TV bands, but as analogue TV gives way to digital, these spare channels will disappear. At least there is now one harmonised European band (1785 - 1800 MHz), which has been set aside for analogue and digital radio microphones. However, it is not completely straight forward as it is shared between different uses in each country, "but it would allow reasonably easy movement around Europe," says Paul Gill, principal engineer, JFMG, which manages the spectrum for programme making and entertainment in the UK on behalf of the Radio Communications Agency. The 1785 - 1800 MHz band "is obviously a bit higher than any current frequencies used for radio microphones. We think, at the moment, that it should be used for the digital radio microphones which are in development," he says. Currently, 470MHz to 862MHz covers the whole European frequency spectrum, but with competing demands from DTV and other spectrum users, the exact frequencies available differ from country to country, as do the regulations. "It is very difficult to come up with a single product that an end-user can use all over Europe," says Aldo Hakligil, managing director, Audio Engineering (which makes the Micron range). "We are forced to manufacture frequency agile units and in one way, maybe, sacrifice the performance of the units to cater for these type of applications," he says. He believes the authorities don't take radio microphone users or manufacturers seriously, especially as other spectrum users pay so much for their licences. One possibility being discussed is moving to an upper UHF band, around 1.8GHz, but Hakligil doesn't think anyone would want to wear a microwave transmitter on their body all day. "There hasn't been enough research into potential harm," he says. It would also require new investment by radio microphone manufacturers. Brian Copsey, chairman of the European Telecommunications Standards Institution Task Group 17 (looking after broadcast service standards), is currently pushing (along with other standards bodies) for an international analogue standard for radio microphones, something which he believes has a "pretty good prospect of happening, eventually." He is also secretary of the Association of Service Providers, which looks after issues in international standards and European frequency allocation on behalf of manufacturers, broadcasters, users and hire companies. International regulations have at least relaxed to the extent that manufacturers can now supply systems which are easier to use in different countries. Sony, for example, is currently rationalising its range, introducing "B" versions of its models which can now handle much wider frequencies. Instead of 8MHz blocks, they cover 24MHz. As standard they are supplied in four base models (based on TV channels 21 - 23, 33 - 35, 62 - 64 and 67 - 69). Special order versions can operate on virtually any other 24MHz frequency block between 470 and 862MHz. "As long as we print what frequencies can be used in each country, we can now sell products which cover a wider range of bands. Basically it is now the customer's responsibility what bands they use, where previously it was the manufacturer's," says Andrew Hingley, senior product manager, professional audio, Sony. "It also means people buying the equipment can use the same microphone in different countries," he says. But, "the regulatory situation is changing all the time, so manufacturers are often having to chase the legal situation." |
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Selling Spectrum"We have been looking at spectrum issues because spectrum for radio microphones will disappear as analogue TV gives way to digital TV," says Copsey. When analogue television is switched off, it is likely that spectrum will be sold off. Many radio microphone users are fixed sites, like TV studios, which are allocated TV channels not used in that area. But if the TV channels are sold off, then radio microphone use will have to be curtailed. "With wideband radio microphone requirements, the powers that be see it as wasteful in terms of spectrum use, whereas you might have eight to ten radio microphone frequencies in an 8MHz band, the government may feel it is better served by selling that bandwidth to other services," says Kishore Patel, managing director, Audio Ltd. "The licensing in these channels is not horrendously expensive, but government may like to get more. An independent report in the UK on spectrum licensing recommended that the current license fee of £160 per channel per year, be increased to about £8,000, which is far too much for a freelance sound recordist," he says. He believes the government doesn't realise how much radio microphones are used for the entertainment industry now. A film set, for example, typically uses a minimum of four channels, up to six, where they used always use boom microphones, because of the freedom wireless offers. "Government believes if mobile phone technology can become more efficient, 'why can't radio microphones?', but the digital technology is not there yet," says Patel. |
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Why Digital?Copsey believes regulators are pressing for digital because "it's a buzzword." "The regulatory bodies are pushing for digital because they think if mobile phones can do it, radio microphones should be able to too," agrees Patel. TG 17 generated the digital standard "because we were asked to by the manufacturers, but I'm not convinced that radio microphones need to go digital. At least, not yet," says Copsey. "Analogue radio microphones can work in 50 channel slots without problems in a spectrum efficient manner," says Copsey. Most non-technical people thought digital would be more efficient and more cost effective, because that is how it performed with CDs and DTV, but he says the reality is different. Because radio microphones need real time transmission, you can't use the most efficient compression as compressing the signal causes delay. "This problem is most noticeable with lip synchronisation in live performances," he says. "The delay is inherent in any form of compression system, but native rate [uncompressed] systems need greater bandwidth." Of course, analogue radio microphones do use a form of compression (companding), but that is effectively lossless. At present, a radio microphone channel uses 200kHz, but digital would need more bandwidth to deliver the same quality, even using compression, says Patel. "Digital can't be more efficient because radio microphones need more than 100 dB dynamic range compared to 40 dB signal-to-noise ratio for vision. It is also easier to compress video than audio, especially when trying to synchronise audio to video, the delay is quite crucial on a live set," he says. The delay means it will also be difficult to mix standard wired microphones with digital. Given that most applications for radio microphones are live, this leaves digital dead for now. "We have two conflicting requirements of: no lip synch delay; and compressed audio. You can't do both with the technology we have now," says Patel. He believes the technology will arrive eventually, possibly in about five years. Gill believes it will be a couple of years before digital kits are in use, but users won't want to buy equipment that can't be used live, so "manufacturers have to crack that problem. If we used more spectrum, you wouldn't need to reduce the bit rate so far, but the target bandwidth is the same as analogue, so it needs considerable reduction [compression]," says Gill. The US allows 800kHz bandwidth for digital radio microphones at lower power (half a milliwatt), but this would limit users to only about five radio microphones working together in a multi-channel situation. Within the 1785 - 1800 MHz band, Patel believes that the current specification (with about 400kHz bandwidth per digital channel), would give eight to ten channels in Europe's 15MHz, depending on the technology people employ. "If you allow greater compression, with greater delay, you would get more in. It is probably better to stick to analogue until the technology is worked out," he says. There are only a few digital radio microphones available yet, such as one Sennheiser sells in the US, although that is believed not to be a big seller. Copsey sees spectrum efficiency becoming increasingly important as users are charged for bandwidth, but digital technology can't give that efficiency in real time - yet. Besides, digital costs more and can't compare with the multichannel abilities of analogue. While an analogue system can easily cope with 32 channels at a single event, he doubts whether digital will be able to deliver the same ability cost effectively, or in a spectrum efficient manner. "I'm not convinced that digital technology has much to offer the high-end user with multi-channel systems," he says. "Power consumption is also quite a challenge," adds Gill. Digital is currently confined to the 1785 - 1800 MHz band, "until we have more experience and can look at the compatibility of digital radio microphones with both analogue and digital TV and more importantly other radio microphone systems," says Copsey. Work on this is starting in the next six months. The CEPT (Conference of [46] European Post & Telecommunications administrations responsible for radio spectrum) FM (Frequency Management) 41 Project is looking at not only radio microphones, but also ENG/OB frequencies generally, including microwave links, talkback, and wireless cameras. It is endeavouring to make sure there are frequencies for all these things after the switch from analogue to digital and is aiming for a common solution throughout Europe, says Gill. In Germany, which has 7MHz channels for TV (within 8MHz bands where the remaining 1MHz is used for radio microphones), there will be a problem switching to digital, as the new DTV standard is 8MHz for TV, so there will be no more gaps for radio microphones. The UK has always shared on a complicated basis as it already has 8MHz TV channels, but the broadcasting of DTV alongside analogue has reduced the spectrum for radio microphones. Gill says FM 41 is arguing the case for specific allocation of the UHF spectrum for radio microphones. He is reasonably optimistic that a European-wide solution will be achieved, otherwise national systems will have to be devised yet again. |
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Real World RequirementsFor many users, such as one-man news crews, where the radio microphones are on the camera, spectrum and digital issues are not a problem. "The main issue with these guys is probably robustness and ease of use," says Ian Sadler, sales manager, Top-Teks, which deals with many different manufacturers. Before SX, no camcorders came with a drop in holder for radio microphone receivers, now Sony, Philips and Ikegami offer this, so that users don't have to worry about power or connections. As most models are the same size, he says choice is down to personal preference. But, because the main manufacturers have different connectors, users have to buy a complete kit, including microphone, from one maker. Microphones can be adapted, at a cost, but Sony transmitters don't work with Sennheiser receivers, for example. It also means that if changing a system, users generally have to change everything, although he says that as people tend only to change if they are unhappy with it, that is not such an issue. Cost is, especially for users of low-cost camcorders. "A DV camera costs £1,500 and a good radio microphone system costs £2,500 for a diversity system. A non-diversity system should be suitable for DV, but they are only about 30% less expensive as you still have to purchase the same transmitter," says Hakligil. Many manufacturers have lower cost systems, but the cheapest are usually too large for on-camera use. Sony has the Freedom range, a non-diversity system which Hingley says has sold to many DVCAM users, and costs about £900. Over recent years, Hakligil has seen "a big decrease in the sale of non-diversity models. We feel the market isn't there any longer." Although he admits he isn't pushing it. Most users buy diversity units, agrees Sadler, unless they are using small, DV-based camcorders, where price is obviously more of an issue. The cheapest kit he sells is Sennheiser's Evolution 500, which is about £500 for transmitter, receiver and lavalier microphone. "It is the cheapest I'd recommend anybody to go with radio microphones. There are cheaper, but they are just not worth it," he believes. |
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WHAT USER'S HAVE TO SAY... |
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Taken To The Wire: Users UnpluggedRadio microphone users get passionate about their equipment. They depend on them for their work, and when a system keeps delivering the goods year after year (and even decade after decade), it is not surprising that they are keen to tell everyone about it. We spoke to three enthusiastic owners. Italian lighting cameraman, Alec Ceschi, has been using his Pastega system for more than ten years, but believes it is still better than newer models from other manufacturers. Now based in London, although his company has four crews in Italy (mainly doing news for RAI), Ceschi doesn't like to do one man shoots, but sometimes has no choice, or works with a camera assistant rather than a sound recordist. He uses the Pastega kit, fitted with a Sennheiser MKE2 capsule, with his Digital Betacam and Betacam SP camcorders, and occasionally with other formats, such as DV, where its small size means "it can fit on the back of any camera," he says. "The system has proved itself time and time again and I repeatedly realised why it is the preferred specification audio kit for RAI and many others throughout the world. It has amazing range and brilliant reliability." In all his world-wide assignments "it has never let me down. Not once. The most memorable time was a few days after I bought it, when we were filming in the Colosseum in Rome, and I suggested a piece-to-camera with the presenter standing at one end of the arena and us at the other and there was absolutely no hint of break-up in transmission and perfect sound clarity. It passed its first test with flying colours," he says. "It has been with me ever since and only had one overhaul. It has delivered in situations like boat-to-boat, plane-to-plane, car-to-car, which are usually very tricky for interference and break-ups in transmission." The only draw-back is its expense (around £3,000 for a similar model now), "but in my opinion they make the best piece of kit I have ever bought." He is not interested in the technology, but in ease of use and reliability. He has used a wide variety of radio microphones from other manufacturers and says the most critical factor in choosing a system is range: "you don't want to hear cracks when you walk 50 metres down the road." |
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Horse SenseEric DeBlackmere is a Director of Photography/Operating Cameraman who has shot documentaries all over the US, the Far East and in the UK. He uses a UHF-band Lectrosonics UCR-190 Receiver/Transmitter package, which he believes offer "the best quality at the best price. I have used this mic system extensively and under varying conditions and have never been disappointed by it. I have never encountered any interference while using it and the audio it delivers is clean and crisp. It is also extremely user friendly, meaning that as a one man band working without an audio technician, I can set up this mic and not worry about it for the rest of the day, allowing me to concentrate on shooting my footage." On one shoot about race horse training, for the Television Games Network, he was positioned on the bed of a truck as the horses galloped along an exercise track. "We miked one of the riders with the wireless mic. It was the only way to get any audio, as we were going to be about 100 feet away from them at all time and any audio taken from the camera position would have been ruined by the sounds of the truck engine. The final footage was incredible, as the mic was able to not only pick up clearly the heaving breath of the horse as it raced along the course, but it clearly picked up the thundering sound of the hooves striking the turf. With tight framing and the audio from the wireless mic, it was impossible to tell how we got the shot." Later on the same shoot an interviewee he had just miked-up was called away for an emergency meeting. "The interviewee and my producer got in a car and drove off, forgetting to turn off the mic. I was able to monitor their every word as they drove one-and-a-half miles away, got out of the car, entered a building, walked through the building and had their meeting. Not once did the signal fade or cut out. It was if they were standing right next to me. That was when I knew I had a great mic system." For him, the most important issues when buying a system are interference and reliability. "I knew beforehand that I would be working in areas that would be saturated with RF emissions. I also needed a system that I could depend upon 100%, without thinking about it," and his Lectrosonics' system does just that. |
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Working In HarmonyFreelance location sound mixer, Richard Merrick, has been working on TV programmes, films and commercials for 30 years (including 28 with the BBC Film Unit) and has used almost every make of radio microphone generally available in the UK, often in large numbers, up to 32 running together at one event (The Children's Prom In The Park), although something like the Eurovision Song Contest uses even more. There is a lot of scope for things to go wrong, but thanks to a computerised frequency plan drawn up by someone like JFMG, it is relatively straight forward. The computer works out where there might be problems with harmonic interference (50MHz, 100MHz and 200MHz are harmonically related, and the biggest problems are caused by thirds). While the core frequencies might be different, their multiples may clash. "The more systems you have, the worse the problem gets." He is currently working on a new location game show for BBC Choice he describes as Big Brother meets Candid Camera, and has just finished an opera and a children's drama. The game show uses a lot of radio microphones, both on people and as links. As the filming is intended to be unobtrusive, including using robotic miniature cameras, they prefer to use radio microphones for sound, talkback and earpieces. He has several radio microphones, including an Audio Ltd 2020 diversity UHF and Audio Engineering Micron VHF models. He calls the Audio Ltd system "state of the art. The range is superb, the quality is superb, they are very flexible, you can do lots with them, they are small, compact and they are reliable - you can't risk missing anything just because the radio microphone is not working for five seconds." The Microns are older, and he uses them more for sending signals the other way, putting the aerials up high. As they are non-diversity systems, they aren't so useful in big buildings with lots of metal work, where they are affected by ghosting, but he used the Audio Ltd diversity system (which picks the best signal from two aerials) at a distance of more than 100 metres in a large metal building recently with no problems. When working abroad, users are supposed to apply to use different frequencies, but the reality is that most users try to use their existing system first, as radio microphones are so low power they are far more likely to be interfered with than affect any other equipment. "In some countries, especially outside Europe (and especially any with a military presence), any mention of radio on a kit list may get you searched, so I tend to put it down as microphone kits and avoid mentioning radio or wireless," he says. When buying or hiring a radio microphone kit, his favourite test is to jangle a bunch of keys in front of the microphone. "If it sounds like someone stomping on cardboard boxes rather than rattling keys, then it isn't too good." The key to good sound is compansion (compression and expansion), how the signal is squeezed before it is sent and expanded in the receiver. "Those two circuits have to match and the tracking has to work." He doesn't think some of the cheaper systems do this very well. April 2001
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