Signal to Noise Ratios

I was thinking about signal to noise ratios.  I don't know why reading The Hobbit would cause me to think about signal to noise ratios, but it does.  Sometimes I have trouble communicating topics like balanced signals and CMRR to people, so I decided to make some graphics to help out.

I made some noise (recorded a quiet room with my laptop's built-in microphone) and then generated a sinusoid in a second track.  The two wave forms are in the first picture (sinusoid on bottom).  The sinusoid has an amplitude that is much greater than the 'noise' signal.  I call it the good signal to noise version.



Then I cut the amplitude of the sinusoid to make what I call the bad signal to noise version (sinusoid on top). Note that in both the good and bad versions the noise level is the same, only the sinusoid level changes.


Then I summed each grouping of two waveforms to create a resultant waveform for both the good and bad signal to noise ratios.  The sum from the 'good' version is on top and the 'bad' is on bottom.  Notice that in the top (good) version you can easily tell what the original sinusoid is.  In the bottom (bad signal to noise ration) version, it is extremely difficult to tell what the original sinusoid signal was.



Now for why it's important.  The noise added to any signal is the same no matter what the level (volume) of the signal is.  Pretend that the sinusoid is what you want to hear (perhaps it is part of a guitar solo).  Most electric guitars have a volume control, as do effects pedals and amplifiers.  Cutting the amplitude of the sinusoid in step 2 is like turning the volume down on your guitar or amplifier.  As you can see in the third picture, when you have a bad signal to noise ratio, you can't really tell what the original signal is, but when you have a good signal to noise ratio that guitar solo comes through really well.

So the next time you're trying to set your volume levels between a source and a sink, try this method.  Play something that is the loudest possible volume you'd ever want, then set the source volume as high as you can without getting unwanted distortion (or damaging any of the equipment), but then back off just a bit.  Backing off just a bit allows for those times when you want to play something just a little bit louder than you did during the loudest part of soundcheck.

Adding a sound volunteer

Today was the first planned solo day for Greg, our new sound guy.  He's run the service once before, but I was behind the board with him then (adjusting the recording mix, but still there).  I had hoped for him to run it solo today with me sitting in a far corner, but it turns out that I am expected to attend family functions, so I was hours away.  It's definitely not the best week to have the record snake multi-pin go out when I don't have time to repair it.

Last night I found out the band leader (who is all wireless) would be gone and the pastor (who is wired) would be standing in for him.  I'm glad that I was able to get everything laid out and plugged in last night, but because the pastor rarely sings & plays guitar during the service I don't have any gain or EQ set up for him.  The mix can get along without the band leader's guitar (not great, but it works), but the pastor's guitar and guitar style are difficult to mix into the rest of the band, especially when he can't be at rehearsals or warm-ups.

I didn't get any calls today, and I'm pretty confident in Greg's mixing abilities, so I doubt anything went wrong.  I hope that's not wishful thinking.  I'm interested to hear his evaluation of how he did.  I'm also hoping that as the pastor and the band start to hear two different people mixing on a more regular basis they'll start to give us a little more input (not feedback) on what they want out of the speakers and monitors.

Praise in the Park

Today my church held worship service in the park across the street.  The park has a bandshell with benches out in front.  We used the contemporary service's equipment because it is mobile (the contemporary service has to get packed away each week).  Because that includes a lot of equipment, the church band (for which I'm the sound guy) began the setup at around 6 AM.

Things that went right:

• We had tarps to set the sound racks on, as well as for the cable drops off of the stage.  There was a lot of dirt instead of grass in some places, so this was a really good thing.  We also had a tent over the sound equipment.
• Orange cones (the short soccer type) on top of the cabling between the sound tent and the stage.  If it had been an indoor location, I would have wanted brightly colored tape to mark which cables to not step on.  And I guess I wouldn't want anyone tripping over them, either.
• The pastor had keys to the bandshell.  This way we were able to open the bathrooms as well as turn on the power.  One of the most important things to me when running sound is to have access to the circuit breakers via whatever means necessary, including taping over door locks.
• Water jugs - it's hot and humid, so this is a requirement.  The water jugs didn't show up early enough for the people setting everything up, but luckily some kind soul found bottles of water for us.
• We have a team of people who know how to set things up - they all know how to do the parts they're usually responsible for, and everyone has enough of an idea of what's going on to be able to help out in other areas on days when everything is different - or at the very least knows who to ask.
• Additional help from church members - normally everything rolls into a closet that's across the hallway. Having a couple of trailers and extra arms to lift and carry things around was a blessing.
• We have speaker and snake cabling that we can use in the park - our usual bulk cabling between the stage and the sound console is permanently attached to the building.  Having an extra stage box with the same multi-pin connector that I could hook directly into the sound console was nice.
• Almost zero feedback in an echoey bandshell.
• I brought a candy bar for my second breakfast, and I keep a bag of beef jerky in one of the rack drawers.  I know at least one other person was munching on breakfast bars.  Food is an essential thing to consider, though it's not always necessary.
• The weather - except that even though we had clear skies, it did slightly sprinkle for about 3 minutes, just enough to see water droplets on the concrete and benches, not enough to be a danger to the equipment.  I didn't even know it had been sprinkling until after it had already stopped.

Things that went wrong (and what we can learn):

• The park sprinklers were still going while we were trying to bring all the equipment in.  Better communication between us and the city could either have told us to start later or gotten the sprinkler sequence turned off for the day.  It might have even been solved by better communication within the church - the worship service was scheduled to start at 9 AM, and the guys who were there at 6 were not involved with reserving the park space.  While it's not important that church/choir/event leaders be fluent in logistics planning, it is important that they know that the logistics is happening and takes time.  I've seen performances cancelled because choir directors were unaware that it took more than 20 minutes to get equipment set up - this church leadership does a decent job of being logistically aware, but it's never something you should leave to chance.
• An old wireless microphone wasn't up to the task.  Luckily, we have plenty of wired microphones around and this wireless was not necessary for the service.  In fact, it's usually not used at all.
• The speakers needed to be turned out a bit more to cover where people were sitting.  Because people brought lawn chairs to sit in instead of the benches, they were outside of the benches.  Perhaps this could have been avoided had I tried to think things through the mindset of the people who were just attending the service, but I got too caught up in planning what cables needed to go where to take a step back.  This is another example of why having a team of people who are involved with the setup and capable of thinking for themselves - it was a band member who turned the top speakers out on his own initiative.  I in my sound cave didn't notice there was a problem, because I had plenty of speakers pointed at me, but there were some parts of the audience that weren't properly covered.
• The snake stage box we used today has fewer channels than the permanently mounted one, and none of the returns are hooked into the multipin connection.  Some instruments are supposed to plug into channels that don't exist on the portable snake, so I had to do a little readjusting at the console inputs and a lot of shouting to the stage about which line goes where (we didn't have the speakers going yet, so I couldn't use the talk-back mic).  I intend to fix most of this with a planned channel reassignment coming sometime soon-ish.
• The bandshell faces east, so many things on stage were in the sun.  This made the metal parts of the drums very hot.  Next time we'll need to take care to keep the guitar stands further back in the shadows (at least, I think it's bad for guitars).  Also, sunglasses are important during times like this - I didn't need them at the sound console, but only one band member had them onstage.  Also, next time the details might be different in such a way that I would need sunglasses.
• One band member brought a pair of FRS radios so he could communicate to me from the stage (tell me what I was doing wrong).  Unfortunately we didn't have the right headset connectors with them, so they weren't much use.  We left them on during the service, but we didn't encounter any problem that was worth blaring over the radio speaker.  Everything else had the correct hook-ups.
• This didn't actually go wrong, but the park across the street is about as far as I'd want to move out equipment.  While it is all on wheels, none of it is in cases.  If we had to travel to another city, or even across town, it would have been a lot more risky.  Unfortunately, storage space at the church is limited and we have to store much equipment on shelves, so I don't see us moving to road cases (nevermind the cost, of course).  I would enjoy taking our band on the road more, but it will require a lot more thought than someone riding on the back of a trailer to hold stuff in place and making 3-4 trips.
• No order of worship - I didn't know what order things happened in until I saw the bulletin, which was when I learned that there would be an additional song I'd never heard before, performed by unknown persons.  I also didn't know a member of the congregation was going to read from scripture until someone asked about a mic for him.  I'm not sure how the band knew when to do which songs.

I thought that the service went very smoothly.  I normally don't get to mix from the middle of the congregation, so today was a nice opportunity to be able to hear people singing along with the praise band.  And not that I have anything against the traditional services, but if some people enjoyed what they experienced today enough to defect over to the contemporary service, even part-time, I won't complain.