I was trying to explain metering and levels on another board recently. I may as well repost that here .. if only to find out if I have misunderstood the nature of these things (yes, there is some generalisation in the following, simply for clarity).
..............
Regarding levels:
The key here is that your analogue gear and your digital meters measure different things on different scales.
The analogue gear will generally use a VU meter. VU stands for Volume Unit. It is a measure of input voltage and gives an RMS (Root Mean Square) reading .. or an average. It measures an average. This is similar to the way we hear sound. If a snare drum goes CRACK quickly, the meter will move and will start to fall again quickly. It may never register the absolute loudest signal on the meters needle. However, use a constant sound (like a sine wave) and the meter will stay in the same place.
OK. A preamp is designed to raise a signal to "line level". This is generally +4dbu or -10dbu depending on the kit (pro or amateur). 0VU will be calibrated to represent line level having been reached.
Of course, what we are recording isn't like a sine wave. We will have peaks that go over 0VU and troughs that are well below (including silence!). Analogue tape had plenty of allowance for peaks before nasty distortion happened.
How about digital?
Well, we go from the preamp to our AD converters (analogue/digital). These expect a line level input. They are looking for something that is around 0VU, but how should they represent that digitally?
Well, in the digital world we need a dynamic range to work with. Each "bit" we use can represent 6db. 16 bits gave us a range of 96db. 24 bits now gives us a range of 144db (huge amounts to play with!).
If we set 0VU to be the maximum, that would make no sense. What would happen to the peaks? We couldn't store them physically as a number!
Most converters are calibrated to set a signal at line level to be -18dbfs (this isn't always true.. there is some variation, but its close enough).
OK, what is this "dbfs" thing? Well, the fs stands for "full scale". It is an absolute number, and absolute volume and is used for storing the volume of a signal so that it can be reproduced by a machine. This is very different from an average level as a guide for a human listener. It's a completely different scale from the one used in the analogue world.
The key here is that 0VU is calibrated to around -18dbfs.
BUT.. remember that 0VU was an average (RMS) reading. So we can target an RMS of around -18dbfs. In practice, this means that there will be peaks above that and troughs (and silence) below that. What we will see on the meters is something that bounces around maybe -12ish and peaks at around -6ish.
That will leave us some headroom to play with compressors, reverb, EQ etc.
I hope this hasn't confused.
..............
Regarding levels:
The key here is that your analogue gear and your digital meters measure different things on different scales.
The analogue gear will generally use a VU meter. VU stands for Volume Unit. It is a measure of input voltage and gives an RMS (Root Mean Square) reading .. or an average. It measures an average. This is similar to the way we hear sound. If a snare drum goes CRACK quickly, the meter will move and will start to fall again quickly. It may never register the absolute loudest signal on the meters needle. However, use a constant sound (like a sine wave) and the meter will stay in the same place.
OK. A preamp is designed to raise a signal to "line level". This is generally +4dbu or -10dbu depending on the kit (pro or amateur). 0VU will be calibrated to represent line level having been reached.
Of course, what we are recording isn't like a sine wave. We will have peaks that go over 0VU and troughs that are well below (including silence!). Analogue tape had plenty of allowance for peaks before nasty distortion happened.
How about digital?
Well, we go from the preamp to our AD converters (analogue/digital). These expect a line level input. They are looking for something that is around 0VU, but how should they represent that digitally?
Well, in the digital world we need a dynamic range to work with. Each "bit" we use can represent 6db. 16 bits gave us a range of 96db. 24 bits now gives us a range of 144db (huge amounts to play with!).
If we set 0VU to be the maximum, that would make no sense. What would happen to the peaks? We couldn't store them physically as a number!
Most converters are calibrated to set a signal at line level to be -18dbfs (this isn't always true.. there is some variation, but its close enough).
OK, what is this "dbfs" thing? Well, the fs stands for "full scale". It is an absolute number, and absolute volume and is used for storing the volume of a signal so that it can be reproduced by a machine. This is very different from an average level as a guide for a human listener. It's a completely different scale from the one used in the analogue world.
The key here is that 0VU is calibrated to around -18dbfs.
BUT.. remember that 0VU was an average (RMS) reading. So we can target an RMS of around -18dbfs. In practice, this means that there will be peaks above that and troughs (and silence) below that. What we will see on the meters is something that bounces around maybe -12ish and peaks at around -6ish.
That will leave us some headroom to play with compressors, reverb, EQ etc.
I hope this hasn't confused.
.
