Hello There,
When i started out in Sound Recording i was confused by the different meters and how you can record at -dB, surely that was impossible? Why record at -12dB on a digital system but aim for 6 on a VU meter? So here is a run down of what it all means.
Digital Systems compared to analogue systems
Digital is obviously here to stay for many reasons but an important note in terms of levels are how the different systems deal with very loud signals.
Sound is always analogue at the source and how we hear it only in between can it be digital.
Analogue recording systems gracefully handle extremely loud signals and slowly get completely messed up. Digital on the other hand just cuts off and dies horribly!. This is due to Sampling theorem and the Dynamic Range of data that can be stored on a sample before it starts to distort. Thus it is very important to have headroom and understand your meter system.
Digital Meters
These range from around -60dB up to 0dB. The zero has no actual value other than the loudest sound that can be free of distortion. When measuring in just dB it is only a representative change like a percentage or ratio compared to another value.
Example: If i said his voice was 20dB higher then hers, it would be his voice is 10 times louder than hers. Just saying my voice is 10dB means nothing unless compared to something else, if i said my voice should be at 10dBu or dBA then it means something. (But it will get it`s own topic soon)
Meters!!
These are different standard for playback purposes and final mixes of program but easily applied to production recording devices.
PPM (Peak Programme Meter - BBC)
Range = 0 to 7
line-up: 4 (needle straight up)
Max level: 6
Each division: 4dBs
Average level: 5
Edit suite/CTA measurement
See a real version of a PPM meter system
VU (Volume Units - USA)
line up:-4 (between 3 & 5 black)
Max level: +4 (Red notch right of 3)
Each division: 1dB
Average level: 0
Analogue VTRs
line-up: 4 (needle straight up)
Max level: 6
Each division: 4dBs
Average level: 5
Edit suite/CTA measurement
See a real version of a PPM meter system
VU (Volume Units - USA)
line up:-4 (between 3 & 5 black)
Max level: +4 (Red notch right of 3)
Each division: 1dB
Average level: 0
Analogue VTRs
Digital
line up: -20
Max level: 0
Each division: Varies
Average level: -14
Digital VTRs, Digital Recorders
See real example of Digital Meter System
As always i hope this answers everything and if not drop a comment below and i shall amend it asap.
Cheers,
Matt
www.soundrolling.com
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