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The PPM hits the end stop

Kevin Hilton 19 August 2010

A needle kicking away against an arc of graduated numerals as a voice speaks to the nation is a potent image of broadcasting and one that sustains even in the digital age. The old fashioned mechanical analogue audio meter is still with us but, as Kevin Hilton reports, the PPM’s future is looking less certain thanks to a combination of technological and commercial pressures. The audio business has embraced digital, data-based technology. But, lurking among the digits and computer files, you’ll still find equipment and techniques from another technical age. The peak programme meter (PPM), and its near-relation the volume unit (VU) meter, are symbols of an old technology that have not gone away because the job they were designed to do is still necessary. Designs have changed over the years; segmented lights, LEDs, bar graphs and plasma displays have all been tried and caught on to an extent but the original moving coil meter with a needle and a quadrant arc of numbers has survived because it works and everyone recognises it. Neither the PPM or the VU is perfect, of course. The old joke has it that VU really stand for “virtually useless” but that shining piece of wit has not stopped it being a mainstay of American broadcasting. The same is true of the PPM in Europe. Everyone is aware of its shortcomings but it has become part of broadcasting language – say “peak between PPM 5 and 6” and people know what you mean. So the decision by the principal manufacturer of electro-mechanical PPMs and VU meters to end production by the end of this year caused a stir in the broadcast community. Sifam Instruments is a small, highly specialised company based in the Devon seaside resort of Torquay. Its workforce is small and highly experienced in precision engineering; many are now approaching retirement age and have been working there since they were teenagers. LEDs and bar graphs have not seen off the original design and layout of analogue meters but the growing need for loudness measurement is pushing technology in the direction of computer displays. Sifam is a brand of Elektron Instruments, which clearly saw the way the business was going. At the end of last year it contacted its customers to say production was coming to an end and offered last-time buy opportunities. An anonymous source says Elektron decided Sifam’s core audio metering business was “no longer viable in this market”. Manufacture of a basic analogue audio level meter, based on the VU principle, has been outsourced to India but production of fully speced PPMs and VU meters in the UK is being run down through this year. Canford has been a major customer of Sifam since the early 1980s. It distributes the meters and supplies other manufacturers, as well as producing the famous “Canford PPMs in a box”. Canford’s co-founder and director of strategy, Iain Elliott, says Sifam wrote to customers in October 2009 announcing it was ceasing production of the 74 dual PPM (pictured). This was followed by another letter saying that all PPM and VU manufacture would end by the middle of 2010. Elliott says making moving coil meters is in something of a “Twilight Zone situation” because “it’s not going anywhere but it’s not falling off a cliff either”. Canford looked into buying the business but ultimately decided against this for a reasons Elliott would not divulge publicly. Instead Canford has bought approximately £¼ million worth of PPMs and VU meters. This will cover major projects, including BBC W1, and supplying regular customers like Calrec Audio, as well as general trade. Specialist manufacturer TSL is also a major user of Sifam products and placed a sizeable last order for PPMs. Chris Exelby, general manager of the company’s professional products group, says this should keep production going for two to three years and provide spares for existing ranges. Exelby says that while older engineers and operators have learned to gauge the visual interpretation of average levels provided by the PPM, a new generation is coming along that is more used to graphical displays. “PPMs are a part of our business that has been declining over the years,” he says. “With the move towards loudness monitoring I see the future being in moving bar graphs.” Loudness, ensuring consistency between different kinds of broadcast programme material, has already made an impact on the world of audio measurement and metering. The EBU PLOUD group has been working on new recommendations for this, building on work laid down by the ITU, and is due to publish its findings in time for IBC. The hope is that the five documents resulting from its research and deliberations will go further in solving the problem of discrepancies in level between heavily compressed commercials and TV programmes with a wider dynamic range. New audio meters based on the first specifications for dealing with loudness, ITU-R BS1770 (Algorithms to measure audio programme loudness and true-peak audio level), are already on the market. Many of these have taken a different approach to metering presentation and this is likely to change again after PLOUD presents its conclusions. Not only will R128, the key recommendation on loudness, have a bearing on current meter design but the EBU’s Expert Community on Audio (ECA), the parent group of PLOUD, is now considering whether to extend the work to look into how metering might be done in the future. Andrew Mason, chairman of the ECA, as well as a member of PLOUD and a senior research and development engineer in the BBC R&D department, says loudness is only a part of this research. “The story is only just beginning,” he comments. “There is a revolutionary move in metering, with peak and true peak to consider as well.” The ECA is due to meet on 12th September to decide whether PLOUD’s work will continue to look into new forms of audio metering. Mason says the process would be as much about education as technological design. “We have to look at how people who are used to a PPM or VU meter will work with a loudness meter,” he explains. “The idea would be to help people migrate away from peak.” Mason adds that peak measurement was originally designed to protect the equipment from being overloaded, resulting in distorted recordings. “What we have to come up with now is an idea for how operators can measure audio signals when they don’t have enough time to use their ears, as they’ve been doing with PPMs.” Metering manufacturer RTW is part of the move towards loudness monitoring. Technical director Mike Kahsnitz says “normal level metering using PPM instruments or VU meters plays an important role in analysing audio with regard to technical standards”. But, he adds, it does not allow for visualising individually perceived loudness when listening to audio, which is why loudness measurement is needed to supplement PPMs and other meters. There is some sentimentality about the potential lose of old fashioned moving coil meters but there is also a practical consideration. Dr John Emmett of development company Broadcast Project Research, who has been closely involved with defining loudness, says the dynamics of movement are important. “How the meter moves is very important,” he explains. “It must be restful to the eye.” Iain Elliott at Canford agrees, saying the needle moving in a quadrant arc is psychologically more effective and attractive than a straight bar. Elliott comments that until a new electronic PPM is developed there will still be a demand for the older design, although he feels bar graph PPMs will continue to exist. TSL is already looking to create a ‘moving coil’ meter on its OLED monitoring platform to compensate for the lose of Sifam meters. Meters will always be a feature of broadcast studios and rack rooms. Is it too sentimental to think that’s no consolation if they don’t look like something Tony Blackburn had in his studio when BBC Radio 1 went on air in 1967? 

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