Beat The Buzz – Guitar Recording Workshop
Is it really possible to eliminate all those annoying hums, buzzes and pops from your recording setup? Yes, it is – and Huw Price has some quiet advice in this Guitar Recording Workshop. Photos by Eva Bensasson.
Keeping noise out of your home recording setup requires a little planning and effort, but it’s absolutely worth it, no matter how high you’re aiming. To greatly simplify things in this article, we’re going to break studio noise problems down into two main categories – hum and interference.
Noise is an issue in the studio environment simply because it makes it so much harder to hear what’s really going on. If there are low-frequency drones or random electrical glitches coming out of your speakers, this will inevitably mask the finer detail of the music you’re trying to record. You’ll also be unable to distinguish between noises that are part of your recording system and those that might be coming from a guitar or bass amp, so you might end up recording parts that are too noisy to use.
This boot-fair bought power conditioner is still going strong.
Worse still, you might discover that the noise inherent to your system is actually making its way to your tape machine or hard disk recorder. If it is, you’re stuck with it forever on all your recordings – and that’s why the noise simply has to go.
Nice, but noisy: watch out for old mains-powered effects
Hum is the most common problem, and it’s the low-frequency noise that’s related to mains or power supply issues. You can identify this because earth hum, in the UK anyway, will have a frequency of 50Hz, which is within a whisker of a low G note. If there’s a problem with a power supply, hum will also occur at multiples of that frequency – ie 100Hz, 150Hz and so on. In the US the hum frequencies will be multiples of 60Hz.
Earth Loops and Guitar Amps
If you’ve ever tried linking up two guitar amps, you will have encountered hum caused by an earth loop. Loads of people get around this by lifting the earth connection from the mains plug of one amp, but this is dangerous and potentially fatal.
An earth connection should be properly attached to the chassis of any piece of audio equipment. If an electrical fault occurs and a live part of the circuit reaches the chassis, it’s then safely transmitted down the mains cable, into the mains plug and then literally goes to ground via a water pipe or a copper spike that has been driven into the earth – and this, of course, should also blow the fuse in your fuse box.
If that live current can’t travel to earth, it will travel through you instead – and, make no mistake, if it goes through your heart then you might find yourself on the dead side of unconscious. So we need to find a way to break earth loops without compromising safety in any way.
Simply plugging one of the amps into a different ring main will not cure the hum because all the earth connections in your house will end up at the same point anyway. The only reliable and safe solution I have found to combine two or more amplifiers is a dedicated isolator/splitter. There are plenty of products to choose from, such as the Radial JX2 Switchbone, Roger Mayer’s Crossroads, or the Framptone Amp Switcher. Buying one of these might cost a little more than simply lifting an earth connection but you’ll get a better sound, you’ll probably get the added benefit of amp switching, and it could quite possibly save your life.
Finding the Quiet Spot
Single-coil guitar pickups pick up more than just string vibrations: they’re also partial to buzzes, electrical noise and garbage from dimmer switches or CRT monitor screens, especially in the control room. The good news is that, like cardioid microphones, pickups are directional. So try slowly turning around until you find the quietest spot, and then hit the Record button.
Identifying the Culprit
Finding the cause of an earth loop in a studio setup is more complicated than with a couple of guitar amps because of the sheer number of audio devices and connections involved. However, with a little patience you can get your system running quietly.
Start by unplugging everything – and I mean ‘unplugging’, not merely switching off, because leaving mains plugs and audio connections in place ensures that the potential for earth loops will still be there.
Next, switch on the power amplifier of your monitoring system or your active monitors. If there’s nothing wrong with the power supply such as old and leaky smoothing caps, the background noise should be negligible.
If everything’s okay, connect your mixing desk or control module to your amp or active monitors by using balanced connections wherever possible. Continue connecting and turning on one piece of equipment at a time in order of priority. You can expect a gradual increase in hiss, but as soon as you hear a sharp increase in hum you’ve got yourself an earth loop – and the last thing you connected is probably the culprit.
Hums are endemic in home studios because lots of semi-professional equipment only provides you with unbalanced connections. Whenever you have the option of using balanced connections, use them!
If you encounter an earth loop with balanced interconnects, see Diagram 2. You can simply disconnect the screen connection at one end of the cable – preferably the output end rather than the input – and your live and return path will still be there.
If you’re forced to connect a balanced unit with an unbalanced one, you can make up a cable to help minimise hum. Take a look at Diagram 3: assuming we’ve got a TRS jack at one end and a TS jack at the other, get some twin core and screen cable and use one core to connect the two tips. Use the other core to connect the ring of the balanced jack to the sleeve of the unbalanced jack, and connect the two sleeves using the screen wire. You can try a 1/8W resistor in series with the screen wire to limit hum currents. If you encounter radio frequency interference, try a 100pF capacitor in parallel with the resistor.
There are occasions when the only guaranteed way to break that ground loop is to use a DI box. The transformer inside these devices effectively isolates the two circuits, so there’s no ‘direct’ connection. Some might fret about deterioration in sound quality, but the extent of that will largely be down to the quality of the transformer itself. It’s not ideal, but sometimes you just have to compromise.
Even if everything’s properly earthed and all your interconnections are sorted, mounting equipment in racks can reawaken all those gremlins. New earth loops can be created when the chassis of two different bits of kit touch each other; they can even end up connected by the metal mounting strip and the fixing bolts. So test each unit and its connections before racking it up, then test again afterwards. If necessary, try using special Humfree-type rack bolt isolators.
Plan your Layout
Before you hook everything up, make sure that you take a little time to draw out a proper design. Wherever possible, you should keep audio cable runs as short as possible. Also, consider the fact that transformers radiate hum fields: the bigger the transformer, the bigger the hum.
Try to keep transformer-loaded equipment like power supplies and amplifiers away from other signal processing equipment. If it’s something like a microphone preamp that needs to sit in your equipment rack, try leaving a 1U or 2U space between the preamp and the next piece of kit in the rack. Also, try to keep audio cables well away from mains cables to avoid hum pickup. Avoid running them next to each other for any distance, and if they do have to cross, then make sure they do it at right angles.
I was engineering in a Spanish studio a few years back with a building site right next door. Not unusually for Spain, the workers had illegally tapped into the main electrical supply, and this spot of free enterprise caused absolute havoc for me. With so many pops and crackles coming down the line whenever they used their construction equipment, everything we recorded sounded like an old 78rpm record.
Maybe you have suffered similar problems when recording at home. Some domestic appliances can be troublesome; in my house the fridge and the tumble drier were always the worst culprits. This was because my studio and kitchen are part of an extension and they previously shared the same electrical ring main. The solution to my problem at home was simple, but it cost me a couple of hundred pounds. I was planning to have a new fuseboard installed anyway, so I asked the electricians to put the old fuseboard in my studio and run a new supply to it. This gave me the potential to run several independent ring mains in my studio room that weren’t connected to any other ring in the house.
If this isn’t a practical solution for you or if, as with the Spanish studio scenario, the source of the interference is coming from outside your house, you might need to buy a power conditioner.
Audio Leads should cross power leads at 90 degrees
Power conditioners shouldn’t be confused with power regulators – although some of them can do both jobs. Power regulators fix the mains voltage rock solid to compensate for fluctuations in the mains. If you’ve ever run a guitar amp in Europe at 220V when the amp’s voltage selector is set to 240V, you’ll know what a difference this can make. A decent power conditioner, on the other hand, should be able to filter out all that dirt that’s contaminating your mains supply, so even if your studio is on a shared ring main or you happen to have those dreadful radio and line noise generating light dimmer switches dotted around the place, your audio kit can run clean.
The good news is that you needn’t spend a fortune on power conditioning. The ART PB (£49) and SP (£99) both feature eight rear outputs for power cables and wall-wart devices. You’ll also get surge and spike protection with RFI and EMI filtering and a front-mounted 15-amp circuit breaker reset switch. Or check out a used Gemini PL-01 or the Samson Powerstrip (£59.70). Power regulators will cost you more: check out the Furman range.
Make sure that you go through all the regular noise reduction tips we’ve given you above before even considering buying a power conditioner, because earth loops also pick up pops, crackles and computer noises as well as hum. Make sure you keep all your connections clean and free of oxidisation, and remember that power conditioners don’t fix earth loops
Tags: DIY, Home, Workshops