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Recording Noise

By | July 20, 2007

You’re listening to episode 32 of The Podcasting Blog, I’m your host Ken Walker and for the next 15 minutes or so we’re gonna talk about ways that you can eliminate electronic noise from your podcast.

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Hey everybody, welcome to the show. If you missed last week’s episode, we’re going over possible noise causing problems and I’m talking about the typical things that I check when I’m troubleshooting a noise problem. In the last episode we talked about external noise problems like actual sound sources that might introduce noise into your podcast, we talked about some of the things that you can do to help eliminate or at least reduce that type of noise, and this week we’re gonna talk about a different type of noise, what I’ll call ‘internal’ noise or noise that is actually generated electronically and has a lot to do with the recording system itself.

This is an area that we can actually get into some pretty deep electronics theory, and I’m by no means an electronic engineer so I’m not gonna attempt to explain all that, so I’ll try to deal with it more in laymen’s terms. I have to say this though, audio equipment operates and transmits information by sending little pulses of electricity, and for right now I’m talking strictly about analog audio. Things like a microphone or an electric guitar.

What that means in a nut shell is that it is susceptible to interference from other electrical sources, like for example a computer, a high voltage cable, certain types of lighting. So there are a lot of factors to consider here and if I can’t fit it all into one episode, we’ll break it into two.

The important thing here is that you understand that electrical devices can interfere with other electrical devices, especially electronic devices. That interference can cause noise.

One of the most common types of noise is from a ground loop. Let’s say you’ve got two devices, and obviously it could be more, but to keep it simple we’ve got two. They are connected together, this could be a mixer and the sound card on your computer. Now that’s almost always a bad way to record but it’ll illustrate this problem for us.

These two devices, the mixer and the computer, are connected together, but somehow there is an alternate route that electricity can take between the two devices, and that causes your hum.

Now, if you’re using Audition or even older versions of Cool Edit Pro, you can actually analyze frequencies and if you do that, you’ll notice a large peak in the 50-60Hz range or even possibly one of its harmonics. If that’s the case, then you’ve probably got a ground loop problem. So how do you fix it?

Well, first of all, unplug everything. Disconnect your whole setup, whether it’s big or small. Electrically disconnect it, and disconnect audio cables too. I wanna mention something at this point, you might have a buddy or find an article online that tells you how to modify your gear by eliminating the ground and that your ground loop problem will disappear, don’t do it. It’s very dangerous, I’ve been shocked by the strings on an electric guitar because of fixes like that. I’ve even been hit on stage when my lips touched a mic. It doesn’t feel good, trust me.

We’re gonna start with the power distribution. Good audio quality starts with a good power distribution center. Fortunately the requirements for podcasters is not the same as for a band where they’ve got to run electricity sometimes a very long distance. Usually you’re plugged in just a few feet from the power source. Think about that though if the need arises for an extension cord, don’t use just any cord.

So here’s what you do. For simplicities sake, I’ve gotta select a specific scenario because there are thousands of possibilities and finding true ground loop problems can be a real bear. Let’s say I’ve got a computer, a Firewire audio capture device, an external mic preamp, and an effects processor, just for fun. I’m gonna turn my computer on. I’ll then make sure that my Firewire card is turned on and load up Audition or whatever application I’m running.

If you can monitor frequencies and levels, do it without anything plugged into the Firewire device. So your checking the noise floor of the device itself. You can even do a recording and see if there is any hum or noise.

More than likely, you’re not gonna have noise especially if the Firewire card is powered by the computer. Once you’ve verified that though, plug in the next device and connect the audio cables. In our example here it would probably be the effects processor. Again, nothing plugged into the input of the effects processor, but the output of the effects processor is plugged into the input of the Firewire card. Again, check your noise levels, and what we’re doing here applies really to any type of electronic noise like a hum or buzz, we’re just specifically troubleshooting a possible ground loop.

If you notice the hum at this point, don’t write the equipment off as being bad just yet, there are some things to check. Make sure your audio cables do not run parallel with power cables, in fact, it’s best if they don’t touch at all. If they have to touch, make sure they cross each other at right angles. This minimizes interference from the electrical lines.

Also, make sure the audio cables don’t pass over the equipment. Inside external audio equipment like an effects processor or compressor, there is a power supply. Pay attention to where you plug the power cable into the unit. That’s where the power supply is and your audio cable can pick up hum if it’s too close to that area.

Some other things to avoid, fluorescent lighting, older computer monitors, the big kind. Today’s LCD monitors aren’t a problem but those older ones have some very high voltages going on inside and can cause some problems if your audio cables are too close.

So let’s say that you check all this out and the effects processor still has a hum. Assuming, of course, that you have visual feedback that the hum is in the 50-60Hz range, more than likely there’s a ground problem inside the unit and you might want to get it checked out. To be sure, if you can, take the unit out of the audio chain. Turn it off. Plug in your other equipment, again, one at a time.

If you don’t have any more problem, have the unit checked out, and again, I don’t recommend you use alternate methods of modifying the power cable or anything, there are lift circuits that you can buy that will fix the problem, but that still isn’t the safest thing you can do, for either your equipment or the people operating it. I will give you a link in the show notes to an article on making modifications like this, just for educational purposes, but again I recommend you find an alternate route.

In addition to a ground loop problem, we’ve also got things that I kinda mentioned a minute ago, audio cables touching or being near to power cables, that’s bad. You can have radio interference, so make sure there isn’t anything that emits radio waves, microwave ovens can cause problems, cell phones can cause problems.

Let’s see, another tip is don’t buy cheap audio cables. You don’t have to spend $40 on a guitar cable, but don’t get the $5 ones either. Radio Shack has some real cheap junk, I know they’ve got a line of high priced cables too, but I always recommend you buy your audio cables from a music store. See if you can get shielded cables, and that’ll help reduce your noise and interference as well.

I think I’m gonna stop right here, but definitely check your system out, audio quality is a pretty big deal and anything you can do to eliminate problems like hum or buzz, is always good for your podcast. And let’s face it, people expect the best, so let’s try to give it to them.

Thanks for joining me this week, hopefully this info was helpful to you. Next week I’m not sure what I’m gonna do but I am getting ready to move back to Ohio so I’m gonna be putting the show together a bit early and I don’t have any extra filler shows right now, so hopefully I can get moved and get the studio setup in time to record after next week. I’m gonna start a series on using Camtasia Studio to record a video podcast and I think that’s gonna be a great sequence of tutorials because software training and online presentations is just so popular today, it’s a great way to reach your audience and Camtasia Studio is an excellent tool for that so look for those episodes coming sometime in August. I’m Ken Walker and you’ve been listening to The Podcasting Blog, the podcast that helps you podcast. Email me at podcasting@seocompany.ca or post a comment on the blog. Talk to you next week.

 
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Topics: Audio Hardware, How to Podcast, Signal Processors, Studio | 1 Comment »

One Response to “Recording Noise”

  1. Remi Says:
    August 2nd, 2007 at 2:29 am

    I like your blog,

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