Noise, Hum, Hiss and Whirrrrrrr
by Mark King
Ideally an electric guitar amplification platform would be absolutely quiet in the absence of music. True silence between the notes is one of the most elegant of special effects. Managing noise is one of the biggest hurdles in recording guitar, especially high-gain rocking lead tones where noise comes in many flavors.
HUM
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| 60 CYCLE HUM WAVEFORM |
When I say noise I’m talking about a broad group of unpleasant yucky sounds that I like to minimize as much as possible. Hum is that dreaded constant off-key bass note that drives me insane. The primary frequency of hum is 60 HZ and it’s a parasite of our AC power distribution system. 120 HZ is often found at lower levels riding on top of 60 HZ. Hum is in the air, it’s almost everywhere in some form. Shielded audio cables and metal enclosures attempt to block hum from entering your audio system but it’s a crafty enemy waiting at every turn to spoil your quiet musical passages.
Nowhere is hum more annoying than in a recording studio situation. While there are software solutions for removing hum and noise these are too destructive to the original sound for my taste.
After a lot of expense and experimenting I’ve found that hum should be minimized right from the start. That sounds easy and for a small pedalboard it is, but start adding more guitar amps, more effects, external power, switching systems, direct boxes, mixing consoles and DAWs. Keeping noise to a minimum can be one of the greatest challenges doing a live recording where there is no second chance.
I hate hum, getting rid of it or minimizing it is time consuming and tedius. The physical size of my studio pedalboard is a challenge to work around, changing wiring is like a weird hybrid of technical wizardry and Pilates.
There is no magic bullet, reducing hum means premium power supply connections like the Voodoo Lab Mondo or its equal combined plus quality power supply cables with clean plugs. Galvanic isolation between the power supply outputs kills ground loops that occur in your power supply distribution. If you have hum in your power supply you can’t gate it out. Kill it at its source, if you’re going for lowest hum and noise a real isolated power supply is a necessity.
Tracking down hum can be a real time killer. You must start at the begining of the pedalboard with only the first effect connected, and then add one effect at a time, carefully checking for hum using headphones after adding each gadget.
HISS
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| HISS WAVEFORM |
Hiss is that rush of high frequency air escaping sound. Hiss does not have pitch, it’s just a blast of the second most annoying noise in the recording process. It is up to you to decide how much hiss is acceptable.
Hiss can be gated out to reduce it. The problem with any noise gate is what happens around the threshold of the gate, something called “chatter” or “flutter”. It’s the gate trying to distinguish between whether it should be open to let music through or close to block the noise. It’s usually a fine line between what you don’t want and what you do want combined with some compromise and user input.
A noise gate can help tame the noise inherent with a high-gain distortion pedal. The 5150 distortion pedal comes with an adjustable gate built in because the high gain preamp section of this pedal makes a lot of noise.
Inexpensive noise gates can be real tone killers. The cheapest ones cut off and choke your notes even when the gate is open. When the gate closes there can be a lot of chatter since the detector system in these pedals is just a simple diode. A cheap purchase price often means poor performance and this is well displayed in the realm of budget noise gate pedals.
WHIRRRRRRRRRR
Some pedals use a circuit called a “charge pump” to increase their internal working voltage. Charge pumps are used in cheap pedals and expensive pedals, it’s just a circuit that causes a certain power supply noise to occur in daisy chain power distribution systems.
If you add a new pedal to your system and the moment you plug the power cable into your pedalboard power supply you start to hear a high frequency tone, a steady higher pitched, continuous whirrrrring sound, you just found a charge pump. The only cure to get rid of the whirrrrrr is a standalone power supply for the charge pumped pedal or a high current multiple output power supply like the Voodoo Lab Mondo with 100% galvanic isolation between outputs.
I read equipment reviews where people seem confused and misguided about whirrrrr. It is one of the easiest noise problems to fix but the cure can be annoying. A second power supply makes a portable pedalboard more difficult to connect for live shows. A power supply like the Mondo is costly and takes up space. It is up to you to find the right compromise in terms of size and performance.
Whirrrrr is 100% cureable. Put the offending pedal on its own power supply or get a multiple output power supply that has true isolation, problem solved. Now get on with creating some music.
EPILOGUE
This brings the Pedalboard Power series to a conclusion. I hope some of this knowledge helps in your electronic musical journey.
Part Three, What are Pedalboard Power Supplies?
Part Four, Pedalboard Power Cables and Connectors
Part Five, Pedalboard Noise, Hum, Hiss and Whirrrrr <- You are here
This article is ©2021 by Mark King. It's not ok to copy or quote without written permission, Thanks for reading High on Technology.
Good Music to You!
