D Is for Details - EMusician

D Is for Details

If the devil is in the details, then Old Scratch must stay busy in the audio world. We deal with so many details and so much confusion that it is amazing
Author:
Publish date:

If the devil is in the details, then Old Scratch must stay busy in the audio world. We deal with so many details and so much confusion that it is amazing we manage to get anything done. Confusion can result from the complexity of details, from the lack of sufficiently detailed information, or simply from not paying attention to simple details.

A classic example of confusion due to complexity is the subject of AC grounding. Most of us understand that ground loops occur when there are multiple paths to ground in an audio system. That seems simple enough, but things get more challenging when one attempts to put a proper grounding scheme into practice. It's not so easy to figure out how to be rigorous with such a scheme when faced with long cable runs, components that can be interconnected in a variety of ways, and pieces of equipment that have differing internal ground systems.

An offshoot of this problem is the question of how to interface unbalanced connectors with equipment that has balanced I/O. Are the connections transformer-coupled or transformerless? Should you connect the “cold” conductor to the shield, leave the shield unconnected at one end, or connect only the shield to the connector shell? And so on.

The confusion that results from a lack of sufficient information can easily be seen by people attempting to take measurements. It's not that measurements are difficult, but it is important to dot all the i's and cross all the t's for them to be meaningful, and there are a lot of i's and t's involved in setting up a valid measurement.

Truly wondrous to me, though, are the questions that were resolved years ago that remain questions nonetheless. For instance, why is there still a pin 2-/pin 3-hot controversy with XLR connectors? Pin 2 should be hot according to the international standard, yet some manufacturers still put out products with pin 3 hot. There are a number of valid reasons a manufacturer might deliberately buck the standard, but there is a standard, and its purpose is to define what is “right.” There should be no controversy.

Here's another case: the confusion surrounding dBV versus dBu or, occasionally, dBm. Admittedly, there are several similar ideas kicking around here, and some of those units of measure were created decades ago for reasons that are irrelevant today — but come on, people! Those units have been well documented and explained for decades, and keeping them straight is not that hard! I recently encountered the confusing question of dBv versus dBV. That one is a little harder to track down. Why? Because that very question emerged so soon after the two measures were introduced that dBv was quickly changed to dBu. The dBv measurement had a short life, and that was a long time ago; why is anybody still talking about it?

Similarly, I have seen a nominally authoritative source assert that the difference between the two most common signal references, -10 dBV and +4 dBu, is 14 dB. The “V” and the “u” mean that two different references are being used; the difference is actually about 11.8 dB. That fact has been in so many Electronic Musician articles that it should be granted Hall of Fame status.

Our field is complex enough as it is. We have to keep track of a lot of fine details just to deal with our tools, and perpetuating befuddlement about long-settled issues has no advantages.

Worst of all is when sources of confusion combine — for instance, not paying attention to complex details. Extending that example as an illustration, the voltage reference for 0 dBu is 0.775 volts, according to two international standards. But the dBu reference was derived from the 0 dBm reference, defined as the dissipation of 1 mW into a 600Ω load. That calculates to 0.774596V, a difference of 0.0045 dB. Uh-oh — here comes the fog.

All three sources of confusion cited here can be overcome, although complexity is an ongoing challenge. Although you can choose to deliberately buck the details, when doing so, you risk having to contend with Old Scratch.