Classic "zero VU" level is 1.23V measured on a slow mechanical meter which does not follow speech/music peaks. We added a fudge-factor to allow for the peaks. In AM radio, 10dB was ample: we need a high average level to overcome atmospherics, and occasional clipping is tolerated. Also older technologies clipped softly. In tape recording a clipped peak will be heard many times, 14-16dB was customary lead for "clean" (but tape was often hit harder). In digital, when you use-up all your bits, "dBfs", it clips HARD, so 18dB is often used. Statistics show that zero VU with 18dB headroom will clip only every few years.
Those Dorroughs go to 20dB over a "0 dB" mark chosen to match classic zero VU.
Those Dorroughs go to 20dB over a "0 dB" mark chosen to match classic zero VU.
That chart is wrong or your reading it wrong. 0dbfs is the very max level you can record, you've used up all the bits. It's the last LED on the meter. The nominal level is in VU and is -14dbfs so the last LED on the meter is marked +14db VU The nominal level ( where you want your average level to show on the meter, is -14dbfs. This gives you room for 14db peaks. Or 14db of headroom. Some tape machines in studios are calibrated at -20dbfs for recording where you can have a lot of dynamic range. For mastering music this nominal level has crept up with the loudness wars to as little as -4 dbfs.
What do you want to use the meter for? They are designed for recording and mixing and are not suitable, as many people here believe, for power amp output.
Some terminology problems here. The definition of dBFS is the level of a digital signal relative to a full scale digital sine wave. So, a full scale digital sine wave will by definition have a level of 0dBFS. A full scale square wave will have a level of around +3dBFS.
So, "+18dbfs" cannot be the level of anything, digital or analog.
What you might be thinking of is a +18dBu analog signal voltage being equivalent to 0dBFS. That would be a calibration equivalence for a DAC or ADC that handles both analog and digital signals. You can pick whatever voltage level you want to be equivalent to full scale, and there are tradeoffs for the various choices. I think +18dBu is a good idea for full scale, but let's not write "+18dBFS"!
So, "+18dbfs" cannot be the level of anything, digital or analog.
What you might be thinking of is a +18dBu analog signal voltage being equivalent to 0dBFS. That would be a calibration equivalence for a DAC or ADC that handles both analog and digital signals. You can pick whatever voltage level you want to be equivalent to full scale, and there are tradeoffs for the various choices. I think +18dBu is a good idea for full scale, but let's not write "+18dBFS"!
Yeah, that was along the lines I was thinking---0 dbFS is FF---you're out of numbers!
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