No Peaking – WHY to not crank it!

May 31, 2017 by Ben Stowe, CTS

Most of us are familiar with the complimentary lightshow audio equipment like mixers, and amplifiers provide. How exciting and pleasing it is to see colored LEDs (typically a stoplight variety of green, amber and red, but sometimes more creatively colored) bouncing up and down as we rock the dancefloor. For those with vintage tastes, a needle on an analog VU meter serves the purpose. But besides pleasing our inner geek, what are those lights there for? It takes a little more inner geek to wrap our heads around it.

Typically, these meters represent “VU” (Volume Units) or “dBU”, which is a voltage ratio reference. For those that want to toss and turn a little tonight, here’s the geekery.

A value of “0” in VU is defined as one milliwatt (mW) of power cycling at 1000 Hz flowing across 600 ohms of resistance.

Got it? Good… let’s move on to the dBU:

0 “dBU” is equal to 0.775 volts (I rounded to the third decimal place so we can all keep our sanity) across a 600 ohm load.

We see dBUs used to help quantify the difference between consumer and pro audio equipment, and painfully enough, some DJ mixers still use the consumer standard, while we interconnect them to amplifiers that are often using the pro audio standard. What’s the difference you ask? I’m glad you asked. Consumer audio is –10 dBV (approximately –7.8 dBU) and is usually unbalanced whereas pro audio is +4 dBU (or 1.78 dBV) and is balanced. Why does this matter? It matters because we need to quantify what our VU or dBU meter is actually telling us relative to the performance of the entire system.

The meters are a useful tool for optimizing our sound level to have the best signal to noise ratio, while not overdriving any equipment or distorting our signal. This can be particularly useful with powered speakers where we may not be able to see a signal or “peak” indicator on them. If your gain structure is set to match the equipment down the signal chain from your mixer, we can use the mixer’s VU or dBU meter to help monitor the entire system. It can be as simple as a stoplight. Green means go, amber means prepare to stop and red means you went too far.

What happens when we go to far? We “peak” the system, or exceed it’s maximum dynamic range and begin to “clip” (See Illustration above) the system. This can be particularly dangerous with today’s pre-recorded music because it is often already heavily compressed. This can lead to distorted, dangerous signals which at best sound bad, and at worst will damage components in your system.

Ben Stowe, CTS Ben Stowe, CTS (26 Posts)

Ben’s love of electronics and technology led to years of schooling in Electricity, Electronics, Robotics and Lasers. Ben supported himself through school by building and selling strobe lights and other electronic devices. He built his first DJ show largely from scratch and scrap, often repairing broken items others had thrown away because he could not afford to buy new equipment. He holds a Minnesota electrical license, and his AV installs have been featured in almost every major industry trade magazine. His relentless passion for education has led to a number of other certifications and accreditations, including the most widely recognized one in the AV industry, the InfoComm CTS. His love for education inspired him to begin the ProAcademy educational sessions, focused on increasing understanding of AV technologies within the industry. Ben has been involved in a number of technical writings, lectures, presentations, as well as research and development assistance with a number of manufacturers for products, industry wide. He is also a regular contributing author to industry magazines in the United States and Europe. Ben’s presentations have been featured across the world both as a part of industry leading trade shows, and as a presenter for various groups and functions. Some of these events include BPM in the United Kingdom, Mobile Beat, the ADJA National Convention, Wedding MBA, and a national tour as a headlining presenter for an industry magazine. The United States Armed Forces branches have also called upon Ben to provide engineering and training assistance. His highly informational, slightly nerdy and always funny presentation style have made him a favorite at events, while his sincere desire to help people with their application of technology have made him a favorite with them after the event. Ben serves the industry as the President of NLFX Professional, an industry leading supplier of sound, lighting and video systems, a role he has maintained since founding the company in 1993.

Filed Under: Mobile DJ Performance Tips, Sound Engineering for Mobile DJs