Solving Audio Mysteries: 1 – The Perplexing VHS Video

Today begins a series on solving audio production mysteries.  There are two ways of seeing an audio mystery; as an unsolvable problem or as challenge. The challenge area, that’s where you live whether you like it or not.  You work in the realm of wireless microphones, high-end electronics, and frequency manipulation.  In this world, audio mysteries abound.

Your mysteries are things like why you suddenly have wireless interference after having a stable system for three years, why a single rechargeable battery appears to have died in the middle of the sermon even though it was fully charged two hours ago, and why a sound appears to hang in the air long after the drummer hit his tom. These mysteries are part of audio production.

You don’t get the option of claiming a problem is the result of an unfathomable unknown or a little evil audio imp, though I’ve often considered the “imp” possibility, myself.  No, you are handled a mystery and, like a great detective, you must figure out the motive of the murder (murdering your fantastic audio production).  Once that’s done, you must take this a step further and figure out how to avoid it in the future.

The first mystery

Let’s begin with the first audio mystery ever to come my way.  Everything about it is unusual.  The hardest part, in retrospect, is knowing the reason for the mystery was right in front of me the whole night long.

The group of parishioners was expected to be small.  Christmas Eve service at this church was typically a subdued affair.  You might say so small and subdued that the pastor didn’t even need a microphone.

I walked into the candle-lit sanctuary at 6:45pm.  “Fifteen minutes to go before the service, that should be enough prep time,” I thought.  I see Pastor Dan and he says, “Thanks for doing sound tonight.  I’m not going to bother with a microphone.  I figure we’ll only get about twenty people.  Oh, I do need you to play this VHS tape when I ask for it.”  Before I could say anything else, he says “don’t worry about checking the video, I checked it in the system earlier this week.  It’s cued up and ready to go.”

There are two important parts of the story I should now mention;

1. Pastor Dan did know the basics of the audio system, so I took him at his word.
2. I, in my limited wisdom and experience in my early days of audio production, assumed that nothing can go wrong if no one touches the equipment between services.

The Service

The Christmas Eve service was almost over when the pastor said, “Roll the video.”  Have you ever talked to a dog and the dog looked at you and turned its head to the side as if to indicate, “I’m confused.”  I think I did the same thing as the video rolled.  The characters in the video drama were talking but they didn’t sound right.

What do you think when I say the audio to a VHS tape didn’t sound right?

• It’s a VHS tape, it’s probably old and worn out.
• Check the cabling (don’t we say that for everything?)
• The channel EQ was probably jacked so just fix it.

The audio lacked clarity.  The words spoken were audible but not entirely comprehendible.  This was going to feel like a LONG video clip.

Step 1: Look at the pastor.  I figured if he knew the tape sounded like this, he would watch the video.  As I looked up, he was looking back at me.  Uh oh.

Step 2: Check the cabling. Cabling checked!

Step 3: Must be the channel EQ!  Did I mention this was a mystery series?  The EQ settings were all at the default positions.  I tried boosting the mid’s and the high’s because I’d realized that’s what was absent.  No difference.  This was an analog board, it’s not like there was a hidden setting.  Or was there?

The video clip ended, the service ended, and sanctuary emptied, and I was left looking at the mixer thinking, “what did I miss?”

The mystery deepens

Your typical detective story has the investigator leaving the scene of the crime to return to the station where they start talking about witness, suspects, and potential leads.  In my case, I did the same.  That is to say, I went home.

Working through my notes the next afternoon, I decided to call a friend and fellow tech who was at the church last night.  “Jeff, it’s Chris.  Did you hear the messed up video last night?” “I did and I was in the sanctuary today and everything in the booth looked good.”  We had a day to go before the regular church service.  Things were not looking good.

One important note; while Jeff and I knew how to run sound in our church, looking back, there was a lot we didn’t know.

The next morning, I got a text message from Jeff, “Fixed.  Low pass filter switch was on.” What low pass filter?  Better yet, what’s a low pass filter?

In a follow-up email, Jeff explained that he and a few friends were out late at the church and playing together, musicians that they were, when he starting running audio through the sound system and “…I was getting little to no vocals or guitar, but I was getting the bass pieces out of the drum kit clearly.  All sound coming through the monitors through the Aviom system was perfect, so that signal path was good…I verified signal lights were blinking appropriately on the mixer, house EQ, Aviom and amp.  All checked out.  [Finally] I systematically looked at each button and knob.  When I got to the [house] LPF switch I didn’t know what it was, everything else looked OK, so I tried flipping the switch, and sound was restored.  It wasn’t until later that I consulted the manual to see what LPF stands for.  I should have remembered…but at 1:00 in the morning the brain wasn’t working too well.”

LPF…on a board-wide master send output, ON AN ANALOG CONSOLE!?!

Mystery solved and lessons learned

Our analog mixing console, the old standard Mackie that many of you have used / still use, has a recessed LPF (low pass filter) switch.  While I understand why it would be recessed, still to this day I can’t imagine why it would have one.  I’ve heard a reason or two but I don’t think that are good reasons.

Time for a bit of reflection

There are two key bits of information to take away from today’s solved mystery.

1. Know what every knob, switch, and setting does on your console whether you use it or not.
2. Know that sooner or later, something will get changed and by knowing the settings of your equipment, you’ll know where to look to solve the problem.  I’ve seen this on everything from mixing consoles to recording units.

One mystery still remains in this story. We never discovered who flipped the LPF switch on.

Our next mystery isn’t quite solved and you might be the person with the keys to solving it.