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Old 27th March 2019
Originally Posted by Matt Syson View Post
{So, to sum up this 8 years worth of debate:

Noone knows what the heck +4db/-10db means.

And on that bombshell... }

Not at all.
MANY people know exactly what it means. Some people are away with the faeries but you do need to know the relevance of the two (and there are other) reference levels to the job you are doing.
Some gear produces it's 'best' performance at -10dBV signal level, and some at +4dBu.

+4dBu out of one piece of gear risks overloading (clipping) a -10dBV input.
-10dBV output of a piece of gear risks unnecessary noise (typically hiss) when going into a +4dBu input. If it is a unit that is calibrated for level, compressor , limiter etc, the threshold and other controls will not work at the scale points marked.

Matt S
convert them all to voltage and it starts to make a lot more sense.

dB dBu dBFS dBV to volts audio conversion digital - calculator volt to dBu and dBV dB mW SPL dB decibels 0 dBFS - convert dB volt normal decibels relatioship relation explanation analog audio absolute level true rms convertor converter decibel to dbfs

use the calculator...

+4dBu = 1.22765... Volts (RMS)
-10dBV = 0.31622... Volts (RMS)

What is the headroom specs then? Most gear has anywhere from 15dB to 20dB of headroom (gain above the reference level, before clipping). So

-10dBV + 15dB ~ 20dB (of headroom) = +5dBV ~ +10dBV Max before clipping
+5dBV (using the calculator) = 1.7782 Volts (RMS)
+10dBV = 3.1622 Volts (RMS)

+4dBu + 15dB ~ 20dB (of headroom) = +19dBu ~ +24dBu Max before clipping
+19dBu = 6.9036 Volts (RMS)
+24dBu = 12.2765 Volts (RMS)

So... the max volume before clipping in a -10dBV system is 1.78 Volts to around 3.16 Volts. But, the nominal Level in a +4dBu system is 1.23 Volts, so you can see... sending a +4dBu test tone into a -10dBV system is almost at the point of clipping already. Any spikes from drums or a loud vocal will easily distort the input of the -10dBV system because it is designed to operate on a much lower range/scale of voltage.

In comparison, the +4dBu system doesn't start clipping until somewhere between 6.9 Volts up to around 12.28 Volts. So you can see how a +4dBu system can handle A LOT more level. Why is that good? Because in Analog circuits that can help overcome RF and EMF interference that the copper wiring inside the circuit catches. The end result makes the +4dBu circuits/gear "sound" quieter since the audio signal passing through it is so much louder than the noise being inducted into the circuit from the air.

But the components needed to handle that amount of voltage effectively are always going to be more expensive than the components that aren't designed to handle that much voltage... this is where the "consumer vs professional" delineation came to be between -10dBV and +4dBu.