0 dB Vs -18 dB: The Scoop On Console Metering Levels
If you’ve worked on both analog and digital consoles, you may have noticed that the “target” or “nominal” level on the meters – where the LEDs change from green to yellow on many desks – is often labeled 0 dB or +4 dB on analog consoles, but often labeled -18 dB on digital consoles. What gives
The key is that there are two different decibel scales in play. The unit for analog meters is dBu, which compares signal voltage levels to a reference level of 0.775 volts. That odd value has historical roots, but what matters here is that the mixer’s electronics are generally designed to have the average signal level sitting around 4 dBu, which on most analog consoles is just tickling into the yellow. When mixing, we need some headroom above that “nominal” level to accommodate the peaks in the signal. Generally, the goal is about 18 dB of headroom, so many analog mixers max out around +22 dBu on the main meters.
In the digital world, the concept is the same, but the units are different. Most digital consoles meter in dBFS (decibels Full Scale). A value of 0 dBFS represents the maximum signal level that the digital system can accommodate (before clipping), and the meters show how far the current level is below that limit – that’s why the values are negative. So if we take the same mix into the digital world, and still want to leave 18 dB of headroom, we should shoot for around -18 dBFS on the console meters.
That’s why, even though we can’t draw a direct comparison, it can be helpful to think of +4 dBu and -18 dBFS as rough equivalents when it comes to level targets for mixing. Also worth noting: some digital console manufacturers still choose to show their metering in dBu, often to help retain a more analog “feel.” — Michael Lawrence