A true story and how you can learn from my mistake...It's the middle of the service and I pressed play on the VCR player for a meditational video.  The main speakers broadcast a muddy distant sound.  The VCR was playing but the quality was horrible and almost non-existent.  "I've played this VHS tape before, this shouldn't be happening," I told myself.  The nightmare began...

My initial reaction, outside of "duck and cover," was the output level of the VCR player into the mixer (console) was too low.  "This will be an easy fix," I thought.  "Probably just a bad connection or a bad patch cord."  Checking the cords and connections, a bead of sweat appeared on my forehead.  Cords and connections were ok.

Solving any problem comes down to finding the single source of that problem and the single correction.  Sometimes a problem might take a long time to fix but at its root is one solution.  If I listen to a recording and it sounds fine and the next time I listen to it, it sounds horrible, something - one thing, has changed.

Diagnosing bad sound starts with knowing the reasons for bad sound;

1. Bad quality recording.  In this case, the VHS tape was production quality and I'd recently played it so I could cross that off.
2. Patch cords (cables going from one component to another) have gone bad or connections are loose.  This causes low volumes, no sound, and/or horrible sound.  I'd checked the cables/connections, so that got crosses off.
3. An input or output device is broken.  The VHS player could have broken.  I would have expected it to simply "not work."  The VHS/DVD player is a good name brand and recently purchase so the likelihood of it going bad made it a low probability.  The mixer could have gone bad.  This was also only a few months old.  Possible, but not probable.  That led me to the third component - the house EQ.  Our area had received a lot of lighting from recent bad storms so possibly it was hit.  However, it sits on the same electrical circuit as our other electronics and they would be shot as well.  Lastly, the house EQ is digital so maybe the settings were reset.  Possible, but my gut feeling was this wasn't the culprit - my gut also likes really spicy food so I can't trust it all the time.
4.  Perhaps the simplest of solutions...an input or output component had a setting changed such as a volume pad or pitch change.

As my mind and fingers ran though my list of possibilities, checking and rechecking knobs, switches, and hoping this wasn't a symptom of a $3000 problem, the pastor appeared next to the booth.  Nicely, he asked "any idea what's wrong?"  I shrugged my shoulders in a way that said "I don't know, but I'm giving her all I got, captain!"

I scanned ALL the patch cables into all the components and the mixer.  Then I scanned all the buttons on the board.  Everything SEEMED to be in order.

As a last ditch effort, I turned up the highs and mid's in the channel EQ and cut out the lows.  The audio was now much more intelligible but far from how it should have sounded.

After a few minutes, the video ended and it was back to the pastor.  I took a deep breath and figured I'd work on the problem after the service.
When it rains, it pours.

A bit later in the service, a CD was to be played.  I popped open the CD player, located on a different mixer channel, and cued up the song.  I pressed play and promptly considered throwing the mixer across the room - same symptoms as the VHS player.  I immediately dialed the EQ channel settings and cranked the gain to the max.  I was ready to say the stereo section of the mixer had gone bad.

After the service, I re-checked everything and then went home.  I figured I'd come back the next day with fresh ideas.   That evening, I got a call from a friend who was setting up the stage for an impromptu jam session and said "I can't get any sound from the board."  Initially, he and another guy checked out everything and came up with the same diagnosis I was left with...the digital house EQ was reset and we needed to call our consultant to reload it.

The next morning I got a text message, “Fixed.  Low pass filter switch was on.” 

In an email to me, he explained "My experience was 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."

Have you ever driven by a newly removed tree?  You see the stump but then say "I can't remember that tree when it WAS there?"  So it was when I returned to the sound booth Sunday morning to find the little recessed switch that had caused such a problem.  Our mixer has a recessed switch for the house LPF (low pass filter).  It was turned on which filtered out mid and high frequencies to the main speakers.  It's always off.  It's always been off.  Only trained personnel use the mixer.  There is no reason to change this.  Why did we initially overlook this little button?  Because WE never change it.  WE never had reason to suspect it because WE never use it.  But someone used it.

What You Can Do When it All Goes Wrong:
If you find yourself in the middle of a church service and something goes wrong, follow this short list and you'll get everything back to normal faster than you can say disestablishmentarianism.

1.  Review your mixer for proper settings.  If you need, keep a list handy of all settings so you can reference this when you are stressed (button 1 = on/off or up/down).  In your spare time, read your mixer manual and know what every knob does even if you don't normally use it.
2.  Check your connections.  Have spare cables that have been tested, on the ready.
3.  Check your components for setting changes like pitch control or digital re-sets.
4.  Try to improve the sound quality via channel EQ...this a poor substitute for having things right, but can buy you the time or quality just enough to make it through.
5.  If a component breaks (and this does happen), have a plan.  DVD players also play CD's but if your mixer starts coughing up smoke, you need to swap in another one.  If you don't have a spare, you need a plan.  See here  for more information.
6.  Do what it takes to present the best service despite the circumstances and be prepared to run through everything with a fine tooth comb when it ends.

If you are in charge of the church sound system, consider taping over the switches/knobs that can cause such problems.  Also label knobs/switches as to their use and correct setting if not otherwise clear.

Postscript: The service in which this happened was a seasonal evening service in which we usually don't use extra media.  Our evening services have tended to be simplistic.  Therefore, I showed up at the last minute thinking media wouldn't be used. Typically, I set up and review all media, mic's, and monitors and do a sound check well before a service begins.  Had I done what I usually do, much of this could have been avoided or we could have developed an alternate plan.  ALWAYS do a sound check on everything you will use during a service.  Trust me on this - you really don’t want to find out during the service that something is wrong.