A Question About Decibels

[SonicSynthesis]

I'm reading a book about computer music theory. It says, and i quote, "Generally levels of volume are measured in Decibels (dB), with 0dB being considered the quietest possible level of sound that the human ear can pick up". This statement has confused me because on the mixer in FL Studio it goes from -61dB to +2dB, and 0dB is in no way quiet. Can somebody tell me what's going on here?

[aur3lius]

Yea that doesn't sound right to me. I'm no wiz at audio production so you know, grab some salt, but I always understood 0db to be the point at where music would generally be the loudest. oh actually, well not loudest. It can go louder I guess. But then you'd clip.

You sure you read that right?

[GallenWolf]

I think while the units are the same, in dB, the purposes are different e.g. loudness vs level before clipping.

[SonicSynthesis]

You sure you read that right?

There isn't really any other way to read it, that's the exact words of the text :S

[Ivan Hakštok]

A bit of physics here. The decibels are a measure of ratio between two powers, with the formula L = 10*log(P1/P0). So in other words, a 0 dB value is just a relative term, which in terms of sound would mean that two sounds are of equal loudness.

So when referring to the human hearing, sounds are compared to the lowest loudness a human ear can hear, because it's probably the only valid milestone in loudness levels (there is no max sound a human ear can hear.). But when referring to audio output, it's quite hard to describe a minimum loudness a speaker can produce, so all loudness is compared to a nominal value (the highest one where clipping doesn't occur).

[Rozovian]

Yep, reference points. 0dB is as loud as it gets digitally, before the digital limit kicks in. It's like trying to draw outside the paper -so 0dB is when it touches the edges, positive is when it's outside (which will not sound good in the final file), negative is how far from the edges it is.

This is only a problem with the final output and with effects that can't handle the overflow, and turning the volume down before those effects/the output solves the problem. It's what limiters are for.

In other words, they don't have a lot to do with one another. dBSPL is how loud something is in the real world (sound pressure level), dBFS is loud loud it is to the computer (full scale) - how loud the data is and how much more room there is to make it louder before it clips.

[lazygecko]

dB is only a reference point as has been said. The actual value sound is measured in is pascal. I think 0.000020 pascal was the equivalent of 0 or 1 (can't recall) dB, and the dB value increases on a logarithmic scale. Just using pascal wouldn't be practical because we'd be dealing with some ludicrious numbers.

[Fishy]

0dB means nothing without a reference, which comes after the 'dB' bit. Here's a few definitions for y'all. For those of you that don't know, a 3dB increase is actually doubles the signal level. Try it for yourself, double a mono signal in your DAW of choice and see how much the overall level goes up. It won't sound twice as loud because of the way our ears perceive loudness but the level changes by that much.

0dBFS stands for Decibels Full Scale. That is what your DAW says 0dB is. It means that 0dB will be the highest signal you can have without clipping. Signals half that level will be -3dBFS and one quarter that level will be -6dBFS etc. dBFS only applies to digital signals.

dBSPL is a measure of the acoustic 'sound pressure level'. That's where your 0dB is the threshold of hearing comes from. It is referenced to 20 micro Pascals of pressure. Every 3dB above this is twice as loud etc.

dBA is the same as SPL, but weighted for human hearing (against an A-weighting curve). This means that all frequencies are normalized so that a 40Hz sine tone measured at 60dBA will sound as loud as a 1kHz tone at 60dBa (even though the actual SPL for the 40Hz tone will be much higher).

So most background noise in offices would be something like 40-50dBA. 90dBA is where things are very very loud. 105dBA and up and we're talking hearing damage.

And 1dBA is about the smallest change in level we can hear.

Hope that was useful.