When I first started mixing, I had an interface and a pair of monitors, but something didn’t sound right. The audio wasn’t as loud, full, and rounded as I knew it could be. I did some research, and it seemed my connections were mismatched: My interface sported unbalanced outputs, while the monitors boasted balanced inputs. Herein lay the problem, right?
Right—but also wrong. As it was explained to me by the pro-audio dealer, the primary problem turned out to be a matter of signal level (-10 dBV versus +4 dBu). Balanced versus Unbalanced connections did play a part, but when the dealers explained the difference, my brain checked out. I just bought what they sold me: a box that safely raised my interface’s -10 dBV signal by 14 decibels without harmful noise-floor side effects, thereby giving me the appropriate signal of +4 dBu.
Except it wasn’t a difference of 14 decibels. The difference between -10 dBV and +4 dBu is more like 11.79 decibels. Confused yet? Never fear! In this article, we’re going to clear up the differences between -10 dBV and +4 dBu. While we’re at it, we’re going to demystify the principles behind balanced and unbalanced cabling, and go into why the two are often mixed up.
-10 dBV: The History, the Number, and the Importance of an Upper-Case “V”
-10 dBV is a measurement of signal level, describing the standard operating level of consumer-oriented audio equipment. In the past, such gear sported a lower output level than professional pieces, primarily to save money in assembly.
However, some interfaces still carry -10 dBV outputs, as do the insert jacks of some pro-level gear. The reasons for this are not necessarily cost saving, but for integrating desirable -10 dBV gear into an otherwise pro setup (for instance, inserting a unique effects pedal, or running signal through the RNC compressor).
Now, the “-10” in -10 dBV is simple enough to grasp: “-10” refers to “10 less than zero.” But keep in mind that decibel measurements are descriptions of ratios; we would not say “10 dB" without first establishing a reference point, just as we wouldn’t tell a police officer we were only going “30 miles” to describe our speed after being pulled over. We’d say we were going “30 miles per hour.”
Here we come to the “V” in “dBV.” “0 dBV” stands for “1 volt of alternating current (AC), regardless of any impedance load.” Simplistically speaking, volts in this circumstance describe force. Since the soundwaves are creating a forceful disturbance in the air, this makes sense.
Or maybe it doesn’t; science can be boring, sure. So, here’s what you must know about this measurement: The “V” remains capitalized. If, in a manual or on a piece of gear, you come across “-10 dBv ” where you’d expect to see “-10 dBV,” you should clear this up with the manufacturer, for dBv is different! 0 dBv refers to 0.775 volts of alternating current (AC) into a 600-Ohm load. Not only are the correlations different, but an impedance value is specified, to boot. In keeping with earlier metaphors, think of this like going 60 mph into strong headwinds, which might cause a variation in the overall speed.
What a coincidence! The discussion of dBv versus dBV takes us neatly into…
+4 dBu: The History, the Number, and the Importance of a Lower-Case “u”
+4 dBu is another measurement of standard operating signal level. In this case, it often describes pro audio gear. Yes, +4 dBu is innately louder than -10 dBV. But it’s not 14 decibels louder, and that’s because 0 dBu stands for “0.775 volts of alternating current into an unterminated load.”
The history behind this is measurement is a bit meandering, but here’s the takeaway: The “u” representing “unterminated” is a relative newcomer. Previously, you’d either see a voltage-value of dBv (described above), or its power-related cousin, dBm (0 dBm = 1 milliwatt per 0.775 volts of alternating current into a 600-Ohm load—try saying that five times fast).
When it comes to signal level measurement, these abbreviations were the trailblazers of pro audio gear. But the gear itself changed, spec’d more and more often at impedances higher than 600 Ohms. Muddying these waters further were the inevitable confusions between dBV and dBv. The switch, then, to dBu, unbound the measurement from its more confusing, and somewhat antiquated, predecessors.
Now we can understand why the difference between -10 dBV and +4 dBu is only 11.79 decibels: It’s the discrepancy between 1 and 0.775, which are, in fact, two different numbers (though this almost 12-dB disparity doesn’t indicate you’ll hear a difference of 12 dB, because of the entirely different matter of dB SPL—decibels of sound pressure level).
Whew! Confusing, eh? Just remember this, and you’ll be fine:
- -10 dBV is a measurement of standard operating signal level, expressed in volts of AC, disregarding impedance values.
- +4 dBu is also a measurement of operating signal level, but 0 dBu relates to 0.775 volts of AC, suggesting an impedance value all the while, if not specifying exactly what that number is.
Here’s your practical takeaway:
- If you’re feeding a +4 dBu signal into a -10 dBV input, you’re running hot levels into receivers not necessarily equipped to handle them. Turning the +4dBu level down is a good idea.
- The reverse is also true; if you connect a -10 dBV signal into a +4 dBu input, you’ll want to raise the -10 dBV signal—however, beware: You will also be raising the noise-floor of the signal, which, depending on the consumer-level piece of gear, might degrade the sound.
In fact, it might serve you well to let a discrete, impedance-matched device handle the task for you—a device like this. Note that this product advertises itself as an “unbalanced to balanced” converter.
And here we smash-cut to…
Balanced and Unbalanced Are Different from -10 dBV and +4 dBu
While they often go together like a string of nonsense syllables sung by Olivia Newton-John Travolta in a horrible musical, they’re not the same thing. -10 dBV and +4 dBu pertain to signal level. “Balanced” and “unbalanced” have nothing to do with signal level, and everything to do with signal transference. One’s the what, the other’s the how.
Unbalanced cables hold two wires in their wrapping: The signal and a ground wire, which protects the signal from extraneous noise—up to a point.
Enter balanced connections and balanced cables. They utilize a three-pronged approach in mitigating noise. Along with the ground wire, a balanced connection feeds two copies of your original signal to separate, discrete wires, flipping one of the copies in polarity. The result? Silence, due to phase cancellation.
Now, these two wires, the sum of which is silence, may very well pick up unwanted noise on their run. But what’s good for the signal’s goose is great for the noise’s gander: When the receiving gear restores polarity of the signal to its original state, the signal comes back—and the noise cancels out.
This is the advantage of a balanced connection (though mastering engineers might tell you of their disadvantages—and that’s a whole other article). Therefore, balanced connection points like XLR and TRS (which provide the three wires necessary in the balancing act) often find their way into +4-dBu calibrated gear, and vice versa.
What the terms “+4 dBu” and “balanced” have in common is that they are both considered professional grade. Just as peanut butter and chocolate are separately, and independently, delicious, so too are these audio concepts complementary in their applications—complementary, but not identical.
Okay! Hopefully, we’ve done our job here, and you know now the difference between -10 dBV, +4 dBu, unbalanced cables, and balanced connections. I did my best to make this English, but I know it’s complicated. So, if you have questions, feel free to ask below, in the Comments section.
