Most people, I think, are pretty confident that they know what the word “zero” means.
If someone were to ask you “what does "zero" mean? What would you say? Most people would probably say it means “nothing.” A total lack of something. For example, if I had no donuts, and someone asked me how many donuts I had, the correct answer would be “Zero. I have zero donuts. A total lack of donuts. And that’s very sad :-)." But the answer would be correct.
Common Times When Zero Does NOT Mean "Nothing"
However, there are times when zero does NOT mean a total lack of something. And you are familiar with it. What about temperature? If you see that it is zero degrees Fahrenheit outside, you wouldn’t say there is no temperature. It’s none. A total lack of temperature.” Of course there is temperature. It’s just that the measurement scale in Fahrenheit uses zero to mean something else. Daniel Fahrenheit used zero to measure the lowest temperature he could get a water and salt mixture to reach. Nothing to do with a lack of something.
In Celcius, zero is the freezing point of water.
But as we all know, especially if we live in Fairbanks, Alaska, temperature can get well below zero. It has gotten to -66 degrees in Fairbanks. Yikes! No thank you says this Southern California boy.
OK, so what does this have to do with audio recording?
Well let’s talk about measuring things for a sec. When you measure how long something is, we use inches, feet or miles (or centimeters, meters, and kilometers in all the places that are not the US). You can get a ruler and measure that that half a Subway sandwich is 6 inches. Hmm, a lot of my examples involve food, I just noticed. Anyway… The ruler STARTS at 0 inches (no sandwich at all. Not even a little bit of bread). And the longer the sandwich, the bigger the number.
In audio recording, one of the most important measurements is how loud the audio is. And we use decibels (or dB) to measure that. It would be intuitive to think that total silence - a complete absence of sound - would be 0dB. But as with so many things in audio, it’s a lot more complicated than that (or than it should be in my opinion). Let’s do a teensy bit of explanation without (I hope) making your eyes glaze over.
Decibels (dB) Are Weird
Decibels are not absolute measurements like inches. Decibels are actually ratios. They only mean something when compared to something else. Alright, I see the glaze starting to descend. The point is that 0 decibels CAN mean the absence of sound. For instance, when talking about sound as a possible hazard in the workplace, zero can mean the lowest, and if something gets as loud as 90dB that is the point where it starts to damage human hearing.
However, in audio recording, when we look at the sound levels in our recording software, 0dB is not the bottom, it’s the top. What?! Yeah, it’s the loudest that the audio can go before it overloads things and starts to distort. The reason is that we are talking a different ratio. We’re using something called dBFS, or decibels relative to Full Scale. 0dbFS is the maximum signal level possible. So everything else is measured in negative numbers.
In audio recording and editing software, when you look at the scale on the sides of a wave display - the Y-axis - it will usually say “dB” and not “dBFS,” which would be more correct. So you are just supposed to know that.
Then - as if things weren’t confusing and backwards enough, that “ceiling” of 0dB - the highest level there is, is actually on the scale twice - at the top (which makes sense) AND at the bottom! What? Yup, you have 2 ceilings, one of which is actually the floor? Do NOT think about it. Here is what that is.
We are measuring sound. And the way sound travels through the air is in waves. It’s similar to ripples on a lake. Energy makes water move up and down as the wave moves. Same with sound and air. The sound energy causes air to move back and forth as the wave moves.
And the way we capture sound in a microphone is with a flat membrane - called a diaphragm - inside that moves back and forth as the wave moves through the air. When the diaphragm moves one way, it produces the top half of what you see in the software picture of a wave. And when the diaphragm moves the other way, you get the bottom half. When sound is loud, the wave gets bigger - on both sides.
So you have audio is measured on two sides - one where the back and forth of the diaphragm goes “back” and the other side for “forth.” It might help to think of those machines - seismographs - that measure earthquakes. A needle sits at a starting point in the middle. But as an earthquake starts, the needle moves back and forth, swinging one way and then the other.
Audio Waves ON A Graph
So what does the centerline mean? The dead center line represents silence. And some programs represent that as negative infinity. Basically the black hole of audio? So technically, the quietest audio is in the middle, and it gets louder as it goes up and down until it reaches the top and/or bottom, where it will max out at 0dB. All the loudness levels in between are shown as negative numbers.
So 0dB Is The Loudest Possible Except When...
OK, now that we have THAT cleared up. We will always know what 0 means in audio software, right? Sadly no. Because not all programs use the y axis - the vertical scale on the sides - to show decibels (decibels relative to full scale).
One very popular program is Audacity. If you have listened to me drone on about how 0 means “loudest audio,” and then you look at your wave in Audacity, you’ll be very confused indeed. Because 0 on the Audacity axis will be in the middle. Gah! I thought you said 0 was at the top and bottom?!
I did. But that was when we were talking about dBFS. Audacity is not showing dBs. It is showing "percentage.” But you’d never know that because it doesn’t have any percentage sign or any other way for you to know that. But when you DO know that, it actually does make sense. 0 is total silence, which is actually more intuitive I think. And 1, which represents 100%, is the loudest. 1 would be equivalent to 0dBFS.
So if you see 0 in the middle, it doesn’t mean the Ken was wrong. It means that it’s measuring something different. It would almost be like using inches and feet to measure one thing, then measuring that same thing with millimeter and centimeters. The numbers would be different.
So I hope this helps to clear things up. That is what zero means in audio recording - usually.