Debugging and Tuning

April 4, 2012

Expecting the Worst and Hoping for the Best from Installed Systems

Anthony Grimani ( is president of Performance Media Industries, with offices in Novato and San Anselmo, CA.

It happened again. I went to configure and calibrate a home theater and ran into a quagmire of unexpected issues that caused a failure of the system. One issue wasn’t immediately detectable, and one progressed like a list of bad coincidences from an NTSB airplane crash investigation report.

I have run into speakers with a little fleck of metal stuck on the voice coil at the edge of the gap that started scraping only at high levels and sounded like absolute dread. I have seen connectors with one little stray strand of wire barely shorting between signal and ground– worked fine at low levels but causing more trouble at high levels. I have seen XLR connectors wired every which way, passing signal out of phase and 6dB down in level. I have seen signal ground voltages on products hooked to the same power strip but floating 100mV away from each other, resulting in unrecoverable hum.

Sometimes a debugging problem is obvious after a few minutes; sometimes it takes four hours to find the root cause.

Every one of these little issues has taken down a system in one way or another. Sometimes you still get sound and picture–albeit at reduced quality–and sometimes the system doesn’t work at all. But in just about every case the client was unhappy and withholding final payment. The integrator’s staff diligently tried and tried to find the problem and fix it, but in many cases it was like the proverbial needle in a haystack.

Problems like these often challenge even my engineering experience and abilities. I usually show up with two or three large cases full of test equipment, and at some point along the way, I am chasing aspirin with gulps of coffee while scratching my head and reading the display of my oscilloscope with incredulous disbelief. “What now?!” “No, don’t do this to me!” “Wow, I really don’t know what the heck is up here!” I even spout the ubiquitous “Maybe we should just reboot the system,” in hopes of a magic solution. I test this and measure that. I bypass products, run different cables, swap channels, and verify power line voltage conditions. Sometimes the problem is obvious after a few minutes; sometimes it takes four hours to find the root cause. More often than not, it is a $2 part that is affecting the entire ecosystem of the AV signal.

The fact is that it takes deep knowledge of electrical engineering, audio systems, video systems, power supply systems, and control systems to detect, troubleshoot, and fix the inevitable problems that arise when you have systems with dozens of interconnections, interface compatibility issues, and unpredictable behavior. The technical staff available to many integrators can’t necessarily be expected to have that knowledge base or experience. But you can expect that these little bugs will cost you a ton of money: delays, product swaps, staff time, truck rolls, and the inevitable withholding of payment by your client. At the worst time in a project– when you are spending a bunch of resources to fix problems–you are held hostage by cash flow shortages.

How to Avoid the Problem?

My first suggestion to help avoid problems like these is to establish relationships with skilled and competent consulting AV engineers. You really want someone with a degree in electrical engineering. You want someone who has spent time doing “bench tech” work at some electronics company, and someone who has many years of field troubleshooting experience. I suggest hiring them to do verification and commissioning of each and every system you put together. There is always a problem lurking, and you don’t want your client to be the one to find it. I have now been in front of about 300 systems, and I have not found one that passed all the tests. There are too many parts and pieces at work to ever expect perfection the first time.

So do yourself a favor; when it comes to home theater and AV system debugging and tuning, expect the worst while hoping for the best. Hire the right engineering talent, and read up on the problems.

Chase Walton contributed to this column.

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