Audio 101: dBVU vs dBFS

Hey, guys. Matthew Weiss here — weiss-sound.com, theproaudiofiles.com, and mixing101.co.

I’m going to explain the differences between dBVU, dBFS, and how to convert from one to the other.

So dB stands for decibel. It’s a way of measuring sound energy. VU stands for Volume Unit, and yes, it’s as arbitrary as it sounds, and FS stands for Full Scale, which is not quite as arbitrary.

So let’s start with full scale, because it’s maybe a little bit easier to explain.

In the digital world, we have what’s called a linear system. A linear system means that when you have a signal that’s peaking at say, minus 35 dB Full Scale versus say, minus eight dB Full Scale, while you technically have a louder data point in the system, it’s still the same signal. It hasn’t changed.

The only time it actually changes is when you hit the digital ceiling, which is 0dBFS. There is nothing above that, that is the full scale. You can only go down from there, and anything above it is clipping.

Now, how far you can move down? Well, you can go down pretty darn far. Basically, you can go down as far in level as you want until you start getting to a place where the rounding errors that occur, which is a subject for a completely different video, are actually so loud that they are audible relative to the actual signal itself.

So that’s decibels full scale, and it starts at zero and goes down.

dBVU, Volume Units, that’s an analog measurement, and it’s calibrated however we want. That said, there is a standard calibration, and that standard calibration is 1.228 volts. So what that means is that if you were to take a sine wave generator and you were to crank up 1.228 volts going through your system, that’s where you would want to set your VU meter to read zero.

So 0dBVU equals 1.228 volts, which also equals four decibels U, and the U sounds for unloaded, again, that’s another thing entirely, but that is our standard calibration for the analog world, and most gear is also calibrated to that same standard.

Now, how do we go from decibels full scale, which is a digital measurement, to our decibels volume unit, which is an analog measurement?

Well, again, that’s a bit arbitrary, because we’re working in completely different worlds of existence. The world of full scale is math. It’s simply numbers and data. There isn’t really any inherent power to it or energy to it. What we need is a conversion system that recognizes our decibels full scale, and then says to its own self, “Okay, this is what it’s going to be equal to in terms of volume and voltage.”

So the standard calibration actually fluctuates from converter to converter, so you need to check the specs of your individual converter, but most converters will read anywhere from minus 18 decibels full scale to minus 22 decibels full scale, equals zero dBVU, equals 1.228 volts.

Alright, so check your converters. I use Lynx Auroras. The conversion is minus 18 dBFS equals zero dBVU. So that’s how you get between one and the other.

It’s also important to note that dBVU has a positive and a negative. You can go above zero, and you can go below zero. It goes in both ways. You can have more voltage, or you can have less voltage. What you can’t have is negative voltage, and you can’t have more voltage than what your system can bear.

I mean, you kind of can, but you’re just overloading your system and getting distortion, so something to consider.

But other than that, it’s really not that complicated. It’s simply measures of level in some way, shape, or form.

Alright, guys. Until next time.

Matthew Weiss

Matthew Weiss

Matthew Weiss is a Grammy nominated and Spellemann Award winning audio engineer from Philadelphia. Matthew has mixed songs for Snoop, Sonny Digital, Gorilla Zoe, Uri Caine, Dizzee Rascal, Arrested Development, 9th Wonder, !llmind & more. Get in touch: Weiss-Sound.com.
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