Monday, May 11, 2009

FFW14: Safe, clean power

This was written as a practical follow-up to the previous First Word, ‘Acts of God, and other dirty deeds…’ (FFW13). As much as I enjoyed littering ‘Acts of God…’ with pathetic and regrettable puns, my primary goal was to offer useful advice for protecting audio equipment from lightning and similar electrical events. So in this follow-up I described the numerous devices I used to ensure my equipment was connected to clean and safe power. I’ve always taken electrical powering seriously, not just because of the damage it can do when things go wrong, but because of the effect it has on the end result. Dirty power means dirty signals, plain and simple; but more about that later. The information contained below is still valid and relevant (you can’t change physics!), but I doubt the specific product makes and models are still available. Some of the products mentioned were at least six years old when I wrote this in 2000, which means they were on sale 15 years ago. The chances of finding the same products and manufacturers are remote, at best…

Safe, clean power
In the last issue I discussed the damage caused when lightning strikes a power line, telephone line, or television antenna. This issue I’m going to look at products that protect your equipment from such damage, along with some other helpful power-related devices.

According to the IEEE (Institute of Electronic and Electrical Engineers), a lightning strike on the power lines can deliver up to 20,000 volts and 10,000 amps into a building’s electrical power wiring. Such a sudden and dramatic increase in voltage and current is known as a ‘surge’. The bad news is that surges don’t only come from lightning strikes.

The average home electrical system experiences hundreds of surges every year. The vast majority of these are not from lightning, fortunately, and are therefore not so harmful. They’re created by appliances that contain powerful electric motors and/or heating elements, such as electric heaters, washing machines, dishwashers, air conditioners, refrigerators, and power tools. Whenever such an appliance switches on there is the possibility of a power surge. If your audio system makes a thump or click when an appliance switches on, you’re hearing a surge that has managed to get into the signal path. Although these surges aren’t big enough to cause serious damage (beyond perhaps blowing a fuse), they’re big enough to confuse personal computers and other digital devices, causing them to freeze or crash. They can also make their way into your recorded sound, and may even damage your monitors.

So what can you do about surges? The IEEE recommends two levels of protection. The first is a heavy-duty protector located in your fuse box – where the mains voltage enters the building – for frontline protection against lightning strikes and other externally generated surges. This should be supported by the use of surge protecting power boards that, apart from offering a second level of protection against externally generated surges, also protect your equipment against surges from household appliances.

You will need a qualified electrician to install the surge protection that goes into your fuse box. If that level of protection is too expensive, at least invest in one or two surge protecting power boards. There are a number of these on the market, priced from about $30 upwards. They’re readily available from electronics and electrical retailers, home appliance centres, and hardware stores. If you’ve got a modem connected to your system, be sure to get a board that also includes protection for your telephone line.

It is worth bearing in mind that most of the affordable protection devices use an electronic component called a Metal Oxide Varistor (MOV) to provide the protection. These components are sacrificial: the more surges they encounter, the more they degrade. So before investing in such protection, check that it has a status light to indicate the health of the MOV.

While there are many low cost surge protecting power boards on the market, one that caught my attention is the Panamax series available from Dick Smith Electronics. It’s based on a six-way power board with a ‘Protection OK’ light to show the health of the MOV(s). Modules can be added to include protection for phone lines, antenna and cable TV wiring, RS232 computer interfaces, and more. For a couple of hundred dollars you can put together exactly the system you need.

One step beyond surge protectors are mains filters. The mains power supplied to our buildings contains a lot of electrical noise that, like surges, plays havoc with digital equipment. At the affordable end are passive filters that are usually built into power boards. For a bit more money you can choose from a small number of active designs that provide superior performance. If you’re going to invest in a mains filter, be sure that it also includes surge protection. I have a KCC ‘Squeeky Clean’ LF-3 high-speed power and data filter with active monitoring, which I bought from David Reid Electronics six years ago. It offers protection against surges (including lightning strikes), filters out noise and other interference, protects the phone line, and has some very useful status indicators. A worthwhile investment.

There are two electrical problems that surge protectors and filters can’t protect you from: black-outs and brown-outs. A black-out is a total power failure: the lights go out and everything turns off. A brown-out is when the mains voltage drops, or ‘sags’, significantly. When your lights dim for no apparent reason, that’s a brown-out. Both of these can interrupt your workflow, and may even damage your equipment.

For protection against black-outs and brown-outs, you need an Uninterruptible Power Supply (UPS). This monitors the incoming power and, when it detects a black-out or brown-out, sounds an alarm and instantly generates 240V AC from a built-in rechargeable battery system, allowing your equipment to continue functioning. Most affordable UPS’s can’t generate this replacement power for very long, but it’s enough time to save your work and power down properly. The Sola 305 range, available from Dick Smith Electronics, also includes surge protection, mains filtering, and phone line protection. Priced from $299 to $499, the more expensive models offer longer back-up time. If you’re considering a UPS, be sure to get one with sufficient power rating for your equipment; otherwise, it might only provide a few seconds of backup power.

Apart from the obvious benefits of these products, providing clean power to your system may also improve the sound quality. The KCC filter I use improves the sound of my location recording rig in certain electrically noisy environments. But the biggest sonic improvement I’ve heard from any power device comes from balanced power. I’ve been using the locally-made Peach Audio balanced power supply and filter for the last four years, and it never ceases to amaze me – especially when taking analogue signals from digital sources. Improvements range from subtle to blatantly obvious. Balanced power is also good for minimising the humming and buzzing associated with tube guitar amplifiers, and avoiding certain earth problems. When all else fails, balanced power to the rescue!

So, how can dirty mains power affect the cleanliness of your audio signal? To explain that properly requires a lesson in electricity, which I’m not prepared to give here. Instead, let’s use a simple analogy…

Imagine a mountain with a number of villages on its slopes. Snow falls on the top of the mountain, melts and causes a stream to flow down its side. Each village takes water from the stream for drinking, cooking, washing, sewerage and so on, and tips the dirty water onto the ground, where some finds its way back into the stream. The village at the top gets pure fresh water, directly off the melting snow. The village at the bottom gets a cocktail of freshly melted snow mixed with dirty water from each of the villages upstream. The inhabitants of the top village can safely drink from the stream, but those at the bottom wouldn’t dare! They’ll need to filter and sterilise the water before it is safe for drinking.

The power wiring that runs through our cities, buildings and homes is very much like that mountain stream, beginning at the electricity generator and making its way through our streets. Each house and building draws power from the mains wiring, and some of its unwanted ‘dirty’ power ends up back on the power line. The further downstream you are from the generator, the dirtier your power gets. To make it worse, the people operating the generators are adding ‘dirt’ to the electricity before it even hits the power lines; for example, special signals to control off-peak hot water systems and so on. This is like adding fluoride to the mountain stream to improve the dental health of the villagers – the intentions may be good, but if you don’t want it then you need to filter it out.

Many audio products don’t have sufficient filtering in their internal power supplies to remove these unwanted signals; such filtering adds to the cost of the product but offers no measured differences in laboratory conditions (where the powering is inherently clean), and therefore has no marketing value. Without such filtering, the unwanted signals pass through the internal power supply and manifest as part of the audio signal. In some cases they are clearly audible as clicks, hums and buzzes, in others they form a layer of grit in the background that makes your recordings sound dirtier and cheaper than intended. Your best bet for clean and safe power is a combination of: 1) protection against surges, 2) filtering to remove most of the unwanted dirt, and 3) balanced power to neutralise the effects of any remaining dirt.

Alternatively, do as I’ve done and wean your audio system off the dirty communal mains power altogether. Switch to battery power and say goodbye to hums, buzzes, clicks, pops and all that other grit.

Saturday, May 2, 2009

FFW13: Acts of God, and other dirty deeds…

I’ve always been awestruck by the power of electrical storms, but growing up in the miserable city of Melbourne, Australia, meant I was denied such spectacles for most of my youth. In that godforsaken city, electrical storms manifest as distant rumbles accompanied by harmless flashes of light occurring somewhere behind the many layers of clouds that are permanent residents of the Melbourne skyline; if you were really lucky, you might glimpse some cloud-to-cloud fork lightning, but usually not.

One of the small bonuses of moving to Sydney in 1987 was the chance to experience decent electrical storms, with cloud-to-ground and ground-to-cloud fork lightning being commonplace. Moving North of Sydney revealed even more sky-borne drama. While working in Brisbane as an Audio Operator for World Expo ’88 I enjoyed watching thunderheads build in the afternoon heat, and eagerly anticipated the early evening when they would release their awesome power. In October 1990 I spent an evening picking off leeches in a bamboo hut in Northern Thailand while an absolutely incredible electrical storm passed overhead.

But my favourite electrical storms take place in Kathmandu during the monsoon. I have experienced many of them passing directly overhead; long, low and loud, with lightning that stroboscopes the city and thunder that rattles the windows open… fantastic! But what do electrical storms have to do with audio? Not much, until one hits your house - as discussed in the following First Word, published in issue 13 of AudioTechnology sometime in early 2000.

Acts of God, and other dirty deeds…
It was not unexpected. I was sitting by a window at The Exhibition Hotel enjoying Christmas drinks with some graduates from Sydney’s JMC Academy when, suddenly, I felt my hair standing on end. Moments later, all hell broke loose with a big bang. The windows and doors rattled violently, and the guy next to me sputtered beer down his T-shirt. A barmaid dropped a bottle of Vodka, and a young girl screamed… and screamed again. Some pool cues slapped to the floor, adding to the chaos. Across the road, in Prince Alfred Park, a man fell to his knees, shielding his head as the fractured cover of a street lamp tumbled to the ground and shattered. When it was over, the screaming girl burst into tears, and an elderly woman at the pokies looked around the room, slowly cursing “Holy Mother of Mary” through the haze of her cigarette.

It was definitely not unexpected. I’d been watching the menacing thunderhead of the Cumulonimbus Incus taking shape all afternoon, imagining the chaos inside its dark anvil shape. Warm air rising to the top, forming ice crystals. Cool air falling to the base, forming water droplets. As these air currents moved past each other, I thought about the massive electrical charges building up inside – positive at the top, negative at the bottom. And as the charges built up, I could feel the corresponding positive charge forming on the ground beneath the cloud, tracking its every move like an invisible electrical shadow. It’s enough to make your hair stand on end, literally.

And so the charge builds and builds. If conditions remain suitable, it reaches such an incredibly high voltage that it overcomes the electrical insulation of the air. Can you imagine it? Millions of volts punching thousands of amps through the very air we breathe, sending a lightning bolt slamming into the ground at 96,000 kilometres per second. It would be silent if it weren’t for the heat – and I do mean ‘heat’. A lightning bolt’s temperature exceeds 22,000° Celsius! It instantaneously superheats the air it passes through, causing a rapid expansion and contraction of air pressure. And thus we get thunder, the sound of the sky being torn apart. Mother Nature’s way of reminding us that, despite our mastery of electricity, she’s still holding the electrodes.

A direct hit from one of these things could short-circuit your life. But luckily, what we experienced was not a direct hit. The lightning bolt struck a tall metal street lamp in the park across the road, about 20m away, producing intense stroboscopic flashes of pink light – pink being a telltale sign of rain in the cloud – accompanied by a crack of thunder that easily qualified as the loudest thing I’ve ever heard. The top end was like four horsemen cracking their whips in your face, while the bottom end would give even the most affluent DJ a wet dream – or perhaps just wet pants. And then, that familiar smell of high voltage in the air, a smell I remember from poking around in the back of old televisions, and working inside high voltage substations. Dangerous stuff… “Armageddon outa here!” I joked to the guy sitting next to me, but he was too busy mopping up his beer.

This particular lightning bolt hit a street lamp, and, apart from scaring a lot of people, there was no real harm done: one damaged street lamp, one smashed bottle of Vodka, a stained T-shirt, and a lot of frayed nerves! But imagine if it hit your telephone line…

No doubt you’ve got a modem connected to your phone line. On the other end of that modem is your personal computer, right? And connected to your personal computer, via numerous electrical interfaces, is your complete studio. One lightning hit on your telephone line and it’s all gone, done, finito! Not to mention what might happen if you’re actually using the studio at the time. Quite a revelation, huh?

I don’t like being a fear monger, but over the last year I’ve heard at least three stories of complete computer-based studios being destroyed by lightning strikes. One acquaintance lost over $100,000 worth of computer-based studio – not even his monitors were spared. Thanks to an inappropriate insurance policy that listed lightning as an ‘act of God’ and therefore not claimable, he’s still out of business. Good one, God!

Your phone line is not the only way lightning can attack your system. Lightning can also strike power lines, so, unless your entire studio runs on batteries, the AC power wiring can provide another path for lightning to get into your system – especially if the electrical wiring in your building is not up to specification. Older buildings, faulty and/or illegal wiring, and so on can all increase your chances of damage.

But wait, there’s more! David Turnbull, an audio technician at the Sydney Opera House, recently told me how lightning hit his neighbour’s TV antenna and found its way into the 240V AC mains wiring, destroying just about every electrical item in their house: TV, VCR, hi-fi system, clock radio, phone, fridge, and so on. If your studio is electrically connected to a VCR with an outdoor antenna on the end of it, lightning gets another chance to ruin your day.

Now that I’ve got you totally paranoid, what can you do about it? Tracey Thorn sums it up nicely when she sings “I’ll stand in front of you and take the force of the blow”. You need protection against such massive attacks. And it’s not difficult to achieve.

Prevention is always better than cure. Considering that you can’t prevent lightning from happening, your next best option is to prevent it from getting into your system. The safest thing you can do is disconnect your studio from the power point, phone line and/or TV antenna whenever there’s an electrical storm in your area. But that’s not particularly productive, and it’s not particularly effective if you’re not there when the storm hits!

A smarter option is to invest in proper electrical protection. Apart from protecting your system, it may also improve the stability and sound of your digital equipment. But more about that next issue. For now, keep your eye on the sky. Oh, and do take a second look at your insurance policy. Lightning may seem like the work of the devil, but apparently it’s an act of God…

One of my favourite audio past-times is to record the sound of electrical storms, but it’s not an easy task. Thunderclaps are deceptively difficult to record. They may seem easy because the thunder usually arrives a couple of seconds after a lightning flash, so you get a good indication of when to enter record mode (it is especially helpful if your recorder has a pre-record buffer like my Nagra V, which seamlessly appends the previous 20 seconds of audio to the recorded file so I don’t miss a thing). The difficulty begins with getting the levels right, because each thunderclap is unique and doesn’t provide a soundcheck. To make the task even more frustrating and disappointing, very loud thunderclaps are often distorted before they reach the microphone. Why? Because at very high sound pressure levels the air itself distorts. How?

As you may know, sound energy travels through the air as a series of compressions (i.e. increases) and rarefactions (i.e. decreases) of atmospheric pressure. Although the air can be compressed considerably, it can only be rarefied until it reaches a vacuum, at which point it literally runs out of headroom and clips. This occurs at approximately 170dB SPL. Any sound energy exceeding this point is clipped on the rarefactions and, assuming your recording/editing system is wired in correct polarity throughout, you will see the clipping on the negative half cycles of the waveform only. Bear in mind, however, that it can be difficult to identify the clipping when viewing the waveform due to the air’s absorption of high frequencies over distance, which tends to ‘round out’ the clipped waveform as if it were passed through a low pass filter – which is, in fact, exactly what the air is doing. You can hear the clipping, but you can’t always see it. People who record explosions (including large fireworks) and rocket launches face the same problem.

Other factors to consider when attempting to capture The Perfect Thunderclap are the enormously high static discharges in the air, which can reputedly induce preamp-overloading surges in microphone cables (although I have never experienced this), and the possibility of power blackouts, which render mains-powered recording systems useless. Furthermore, to minimise comb filtering due to reflections from the ground and other nearby surfaces, it makes sense to use a very tall microphone stand and position it in an open space away from other buildings, preferably on top of the tallest building in the area – just like a lightning rod connected to your head via your headphones and recording gear. Maybe that’s not such a good idea…

When I was about nine years old my parents gave me a copy of
The How & Why Wonder Book of Electricity, and I became fascinated with Benjamin Franklin’s lightning experiment with the kite, the wire and the key. By the age of 12 I had failed to repeat the experiment on numerous occasions. My kite, complete with wire and key, remained hidden under my bed, ready and waiting for the next electrical storm. But unfortunately I grew up in the outer suburbs of Melbourne (as mentioned at the start of this Famous First Word), where thunderstorms rarely have the required combination of wind and fork lightning to get a kite off the ground, let alone struck. I should probably be thankful for that…