If you have a powerful enough amplifier and big enough speakers, there's no limit to how loud you can go. Well, I suppose when the air starts to ionize, that might be a problem. But other than that you can go as loud as you like, or as health and safety regulations permit.
But what about inside your digital audio workstation? How high can the level go?
Well the common answer to that question is 0 dBFS. 'dB' obviously stands for decibels; 'FS' stands for 'full scale'.
0 dBFS means zero decibels below full scale; in other words FULL SCALE – it's as high as the signal level can go.
But that's not entirely true…
Suppose you have recorded a signal and you optimized the gain of your preamp so perfectly that it peaks at exactly 0 dBFS. Surely that's as loud as it can go?
OK, let's try a test. Set the channel fader to 0 dB (which means that it doesn't change the signal level) and the master fader also to 0 dB.
Now try pushing the fader up on the channel. Push it up 10 dB. You will notice now that the meters by the master fader are now flashing bright red. That ought to tell you that something is wrong.
Indeed it is a warning. If you now bounce what you have done to disk, the output file will sound terribly distorted on playback. That is because you have tried to go beyond 0 dBFS. And you have failed because you can't go beyond 0 dBFS in the output file. The result is horrible-sounding clipping where the peaks of the waveform have been chopped off.
But go back to your master fader and lower it by 10 dB, or maybe a tiny smidge more just to be on the safe side. The red lights have gone out, haven't they?
As you listen to your signal, it sounds clean. Bounce it to disk and play back the output file. It still sounds clean, doesn't it.
So in the channel you have pushed the signal level up beyond 0 dBFS, which was supposed to be full scale. But since you lowered it again with the master fader you got away with it.
So what's happening?
What is happening is that 0 dBFS refers to full scale in the output file, not in the DAW. In fact, your DAW is probably capable of handling signals up to +30 dBFS, as long as you don't try to output them that high but bring them down again with the master fader.
That extra 30 dB is there as a safety margin, or 'headroom' as we like to call it. The point of having headroom is that you don't intend to use it, but it will get you out of trouble if you need it to.
30 dB is in fact loads of headroom. So there isn't any need for accidental clipping in the output file. Just make sure that the red lights in the meter by the master fader remain entirely off for the full duration of your track.
Over to you… let's hear your red light experiences (!)