Audio Problems

Intro: Audio Problems

Anyone who has ever used technology knows one thing: IT FAILS.  A LOT.  This is more true in the realm of professional audio than in any computer or circuit I have ever worked with.  In this instructable, I hope to teach you some concepts that will help you run audio with as little problems as possible.  Please note that this instructable only covers VERY BASIC problems you can run into with a sound system.  If there is any problem that you would like me to cover, please leave me a comment or contact me.

You can also see my other instructables on sound:
How Sound Works
The Concept Of Sound Pressure (SPL)

Before we go into how to fix problems there are a few things that I strongly believe about sound that you should know.
1.  You can't program sound.
2.  If it can fail, it will.  If there is no way possible for it to fail... then it sill might.
3.  You should know your equipment better than the back of your hand before attempting to troubleshoot.
With that in mind, let's talk audio!

STEP 1: Feedback

Feedback is a howling noise.  It can either be on the high end (very high pitched) or low end (very low pitched).  Feedback is caused when a mic is too loud and is able to "hear itself" in the speaker.  This starts what is called a feedback loop.  Tiny  imperfections in the mic are amplified, and looped over and over again, causing the howling effect.

You can fix feedback by turning the volume on the mic down (the fader on the sound board), turning the gain down (usually the knob at the top), moving the mic behind the speakers, or turning the main fader(s) down.  The preferred way to fix it is to turn the gain down, or the main fader(s).  (The main faders affect your gain structure.)  If you don't know what mic the feedback is coming from, you should use the main fader(s).  To prevent feedback keep your volume and/or gain as low as possible.

STEP 2: Humming

One very common problem in a sound system will be hum.  It is also one of the hardest to troubleshoot.  Hum is especially prevalent whenever a facility installs a sound system as an afterthought.  If you are designing a building and you know that you will have a sound system installed, make sure to have an AV consultant present with your architect.  No doubt there will be some fighting between the two.  When all is done and over with, you will have many compromises between architectural and acoustical, but in the long run it will save you a lot of money and headaches.  Also make sure to have the AV consultant talk to your electrician before any work is done in the room where you will have the sound system.

One of the most common causes of hum is grounding issues.  The soundboard and amps should in an ideal world have a dedicated electric line and ground.  The rest of the sound equipment should also be isolated from the rest of the electric.  If you have computers in your tech booth, try putting a ground lift on each of the computers and see if that helps.  A lot of hum can come from a computers ground.  Whatever you do, do not leave a ground lift on a computer.  Use it for no more than 10 minutes for troubleshooting, and then figure out a way to isolate the ground.  Most ground lifts have a contact to easily redirect the ground.

Another cause of hum is interference.  Even if you are not using wireless technology in your sound system, cables still have problems with RFI (Radio Frequency Interference).  Mute all of the channels on your mixer and bring your mains down.  If you still hear hum, that means that it is coming into your line past the soundboard and it isn't one of your inputs.  If you don't hear the hum anymore, make sure your cables are properly shielded, and start removing cables one by one to see which ones are giving you trouble.  Once you find where you are having problems, try to replace the cable and see if that helps.  When a cable starts to go bad, it can start to hum.

Yet another fix would be to have as little unbalanced signal in your system as possible.  Unbalanced signal is very prone to humming.  The difference between balanced and unbalanced signal is for another discussion, so for now I will just go over the basic cables and whether or not they are balanced.  If I forget to address a cable, please leave it in the comments and I will address it as soon as possible.  XLR is balanced, 1/4 in. and 1/8 in.  (normally used for guitars and headphones) are normally unbalanced, and RCA is unbalanced.  Normally the rule of thumb is if it has two contacts for every channel, it's unbalanced.  If it has 3 for every channel, it's balanced.

A product for fixing grounding hum is called Hum X, a product for 1/4 connections is HE-2 Hum Eliminator (You could also try a Direct Box A.K.A. DI Box), and a more universal product is DTI Hum Eliminator.

There are more ways of fixing hum, but this covers the basics.  If you have more advanced problems, consider hiring an AV consultant.  I personally have worked with All Pro Sound, and really like their staff, knowledge, and business ethic.  I would highly recommend calling and talking to any one of their staff about any problem you might have.

STEP 3: Clipping

Clipping is a distortion caused when the audio going to a component is too hot (loud).  This causes the top of the signal to be "clipped" off.  You should turn down the gain or volume on any adjustment available until the distortion is gone.  Prolonged clipping can cause damage to equipment.

You can compare a "healthy" waveform to a "clipped" waveform in the pictures.

STEP 4: Wireless Problems

Static on a wireless mic is usually caused when the mic is too far away from the receiver, or when something is interfering with the signal.  To fix interference on a mic, you need to adjust the frequency on the mic and receiver to another frequency that is not in use.  (Unless you are a licensed operator that is not restricted by Part 15 of the FCC rules and regulations.)

A good way to get the mic closer to the receiver is to move the receivers to an area backstage.  Many facilities already have wire run from their backstage areas to their tech booth.

STEP 5: Conclusion

There are many problems that can happen when you are running sound.  This instructable only covers a few.  If you want me to add a step on any other problem you might have with sound, please leave a comment or contact me.

If you are serious about sound, I suggest looking at your local library to see if they have any books on sound.  There is no "right" way to do sound.  It is an art form.  As long as it sounds good, then you are doing it the "right" way.  If Picasso did everything the "right" way, we wouldn't be able to view artwork in the same way as we do today.

Please note that I do claim copyright to the information. I did not use any specific sources when compiling this information, all of this is from my personal experience.

You may quote parts of this information for educational purposes. Under no circumstances will you sell this information.

I do not own the copyright to any of the images (except the pictures in step #2), however, as far as I have been able to find, I have the right to use them in this instructable. If there is any question about whether or not I have the right to use these images, please contact me. I have no intention of stealing anyone's intellectual property.

Use of this information implies that you agree to these copyright terms.

© 2011

Comments

[kustermramba]

Hi can you help me solve this? I am using a microphone wireless with 2 volume button, it was working fine earlier because I could use both mics at the same time. But now if I switch on both of them they both don't work, I must switch one off so that the other one work. Please help

[Biggycat1]

Hello! I am so very glad I found your Instructables! Thank you for posting them. They are very informative and well written. At this time I am using an old Radio Shack wireless mic setup, two mics on the same frequency. The mics have switches with three positions: On, Standby and Off. They both need to be on the same frequency, but one mic needs to be on Standby or Off when the other is in use. My problem, and the Owner's Manual warns of this, is that when you move the switch from ON or Standby to Off, there is a loud pop. (There is no pop when you move the switch from STBY to ON, or from ON to STBY). I monitor the amp and always try to anticipate and turn it down when the person holding the mic turns it off. It's too much to ask the person holding the mic to use Standby, plus it saves on the 9 volt battery when in Off. Can you suggest a way to eliminate the "pop" when the mic is switched Off? Can I replace the switch with one that doesn't "pop"? Might I have to modify the small circuit board inside the mics? Any thoughts on this matter will be appreciated.

[kumzyd]

Nice post.. We also have these two wireless microphones which run on the same frequency but they are from different manufacturers. So we can't use both at the same time cos they cause noise at times or one kicks the other away.. Is there a solution to that so the two can be used at the same time?? thanks

[8ball947]

my church has a EURODESK SX2442FX Soundboard. And for some reason the sound is completely bypassing the soundboard while playing music videos and stuff. And we don't know how to fix it. We can not control the volume from the soundboard. We tried muting button and turning volume down with slides. But it doesn't work. We have to turn the volume down manually on the computer. Cause it won't work on the soundboard. Can you please help?

[bricabracwizard]

I have enjoyed reading all your instructables on sound, I look forward to future 'ibles - I like that they are short and concise.

[thegeeke]

I'm glad you enjoyed them! Is there anything specific that you would like me to cover on sound? I'm considering posting a few on some more hands-on topics such as how to run a analog sound board, microphone placement, and things like that, but I am always looking for feedback as to what people are looking for. :)

Thanks again!

[bricabracwizard]

Being a 'layman' I'm not sure how to word correctly the things I would be interested in but all you have listed I would definitely like to learn about. Some things that bother me is interference like hum, picking up radio broadcasts, using over 6 radio mics and how to balance sound in a hall and do you have preferred equipment for a travelling show. As you are so familiar with lighting what would be a great configuration for a travelling show, like DMX, spots, colours - ...... well you did ask! Seriously though, I'm sure whatever you write about will be very informative.

[thegeeke]

Thanks for the suggestions... I will probably add hum to this instructable, and I will be starting a few more instructables very soon! :) After I do a few more about sound, I will start some on lighting. Thanks again!

[S_darnell]

This was the lightbulb graphic that didi it for me! I recently spent a week in the hospital for a knee replacement. Like any good geek I upgraded all my self-entertainment tech prior since I knew I would be bored silly and also unable to crawl around tweaking my environment during recovery. Imagine my horror when I found my new a/v system had an unalterable lisp when using an a/v feed from a cable box in another part of the house. (we live in saudi Arabia..so every trick in the book was used to get a multi input system..the shack is my friend). Finally I googled up "audio problems" which took me to your tutorial. As soon as I read the clipping section I limped out to look at the volumn setting on the cable box. Sure enough, while I was away someone had turned the volume full up. 2 weeks of frustration solved in an instant! Thank you! Sue

[thegeeke]

I'm glad to hear that it helped! :)