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Audio Noise

By | July 13, 2007

You’re listening to Episode 31 of The Podcasting Blog. I’m Ken Walker and this week’s episode was prompted by a comment I had a couple of weeks ago regarding noise, so I figured it would probably be a good thing to feature on the podcast. So this week, I’m gonna deal with you as though you were a client of mine having a noise problem. We’ll start at the beginning and go through every step to isolate and eliminate noise from your podcast.

Here’s a typical situation, I hear this all the time, you’re listening to a podcast and there’s this hum or buzz and it’s pretty constant throughout the podcast. A couple of weeks ago I reviewed a podcast and I mentioned a little hum or buzz problem that they have, and believe me, it’s not nearly as bad as some of the other podcasts I hear out there.

Now first of all, let me state this, having a noise like that, a hum or buzz, will bring your podcast down a notch or two in the eyes of your listeners because it sounds like you’re using cheap gear. And you might be using cheap gear, but even if you are, most of the time, you can eliminate that noise or at least get it down real low.

If someone calls me and they say, ‘Ken, we’ve got noise in our podcast.’ Here’s what I do. First of all, I walk into the recording room. I turn on everything that is on during a typical recording. Then I listen. This is the most important part. Listen. As human beings we take our environment for granted because we’re subject to so much noise.

I do a little hunting once in awhile and I love going out in the woods. You know what I learned very early on about animals. They have great hearing. You know why? Because it’s not usually loud or noisy in their environment. That means their ears are very sensitive.

Well, the opposite holds true for us because we live in busy cities and listen to loud music and our environment is usually not perfectly silent. Plus, we have a tendency to ignore sounds that are constant. We shut them out and almost don’t hear them.

Now why am I talking about environment so much? Because there are two main categories of noise that can affect your recording. External sources, and internal sources. We’ll deal with the internal sources, which is electronically induced noise, in just a minute, but the first thing for us to look at is external sources.

Is the room quiet? Do you hear a PC fan? Most PCs have two fans now adays, a fan for the power supply, and a fan for the CPU. Both of which can be noisy. There’s a whole market of products that reduce the noise of PCs, from super quiet fans to water cooling systems, totally elaborate products. I’ll go ahead and give you a link to just one site that I found that features products like this, but there are tons of them. Always check out the product before you buy! I’m not promoting any sites or any products, I’m just giving you an idea of what’s out there.

So the computer itself is a great place to start. Can you hear it? Why is that important? Because if you can hear it, so can your microphone. Now laptops are notorious for this type of noise. They’ve got a little bitty fan and it spins fast so that it can move enough air to cool those components inside. If you’re recording on a laptop, some of the preventative measures you can take include supporting the laptop on a cooling device so that it doesn’t get so hot. Make sure there’s room for air to circulate underneath the laptop and think about getting a device that will cool it externally.

Listen for other noises though, an air conditioner running in another room or in air ducts. Some of this stuff can be removed with software later, or at least toned down, but it’s way better to get rid of it before hand, if at all possible.

I understand that not everybody can have a nice studio to record in, no big deal, but make the best of what you’ve got. Another nice tool to have is of course some sort of noise gate or downward expander that will ignore the noise when you’re not talking, but again, we’re wanting to see if we can eliminate the source of the noise, and then we deal with things that we can’t fix.

Sit in the room all by yourself, this is what I do. Listen. Is it quiet? If you’re using software that shows you your levels, turn it on. I know Audition is what I record in most of the time, and it shows me audio levels before I record. What are those levels?

Sound levels are measured in what is called dBs or decibels. I won’t get into the theory because who cares about the theories. What we wanna know is, what is loud and what is acceptable. If you can, stop by a Radio Shack or music store and you can actually get a device that will measure your room’s sound level. That way if you don’t use Audition or another software program that shows you accurate levels, you can still get an idea how you stack up to some numbers that I’m gonna give you.

The point at which you can actually hear something, the point that sound is strong enough to vibrate those little bones in your ear, I want you to think about as 0 dB. So at that point, if something gets just a little louder, you’ll be able to hear it.

From that point, things roughly increase exponentially, so some of the numbers I’m gonna give you might not make sense at first, but remember that the dB levels increase exponentially, just like with a guitar amp or a stereo. I don’t wanna get off topic here, but, have you ever noticed that a 100 Watt stereo is not twice as loud as a 50 Watt stereo? It has to do with kinda the same principal, but it’s almost the inverse, and here’s what I mean.

A typical studio, and we’re talking pro studio, is gonna be around 20 dB. That’s pretty quiet. A museum or library might be around 40 dB, but that doesn’t mean it’s twice as loud as the studio. It’s actually about a quarter as loud. Conversational speech is about 60 dB but a typical vacuum cleaner is about 70 dB, the speech is actually half as loud as the vacuum cleaner and I think you’ll agree that a vacuum cleaner is way louder than a typical conversation, especially if you’ve ever tried to carry on a conversation while a vacuum cleaner is running. So you’ve got to understand that relationship there with decibels. It’s not a set amount that is the same from top to bottom, every gain in dB is done on a ratio. A jet, which is like 100 dB, is 8 times as loud as the 70 dB vacuum cleaner.

I know I’m not explaining all of this in depth, but that’s not my goal, my goal is to tell you what numbers to shoot for. If you can get 20 dB, more power to you, 30 is great. Most houses are around 50, but that’s not adequate. If you’re at 50 dB, you’re gonna get lots of atmosphere that you don’t want in your podcast. If you can get below 50, you’ll probably have a great recording.

I’ll mention that in Audition, as well as other recording software, you’re seeing a reference level and the decibel readings are in relation to that reference. So let’s say that the reference is 85 dB, that means that your 0 reading is an 85 dB sound and that means that -15 dB is 15 decibels quieter than your reference, which means it would be 70 dB.

So now I’ve gone off on a bit of a tangent, and I’m gonna take a short break and we’ll see if I can get back to some practical application of all these decibels.


So what does all that mean, well, for starters, it means that if your software is showing you decibel readings in negative numbers, like Audition does, you can’t really know what level you’re talking about unless you know the reference level. Now, in Audition, I believe the reference level is 85 dB, so that means that if your level shows up in Audition as -60 dB, that you’ve got a 25 dB room, because 85 minus 60 is 25. If you’ve got that, you’re doing great.

Remember, a good recording environment is going to be around 15-20 dB, but that’s a good studio. Not a lot of studios even have a noise floor that low.

Now, when I go into a room to troubleshoot a problem like this, I like to take a reading before I do anything, that way, I can say ‘I dropped your noise floor 10 dB!’ or whatever. Sit in the room, don’t move around or talk, take a reading if you can, then isolate problem sources.

When you’ve found and eliminated everything you can think of, take another reading and see how much it helped.

Now, what are some common problems and how do you eliminate them? Well, we’ve already talked about the PC fan and other types of fans. You can get quieter fans, or, if it’s doable, you can separate the mic from the PC by having them in separate rooms.

This is actually what I do because my studio is a room built inside of a room, and if I had the PC in the room, it would raise my noise floor up a bit. Now my PC is liquid cooled and it doesn’t have a single fan in it, but there are still noises like the hard drive. So I’ve got my PC on the other side of one of my walls, and all the cables go through the wall. I get a very quiet room. I’d even do more to it to reduce the sound, but I’m getting ready to move to another state in a couple of weeks, so I’ll wait til I get there.

But you can do the same thing, run a mic cable into an adjacent room if you have to, hit the record button, and walk over to the other room and do your podcast there. You can shut the door, close the window, you don’t have all that equipment. And that can even be a good idea because it’ll change your environment and maybe make it a little ‘less’ studio which some people feel more comfortable in.

Another thing you can do is plug your mic in, put some headphones on and crank the gain up quite a bit and listen to the room amplified, that’ll help you isolate noise problems, and it’ll also help you find a good spot for your mic. There might be directions that your mic just shouldn’t be pointed. So mic position is another way to eliminate noise problems.

Thanks for joining me this week, I hope you can take this information and apply it to your specific situation. Next week we’ll deal with the flip-side and talk about electrical noise and some of the typical noise problems that I find, as well as the solutions. 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: How to Podcast, Sound Isolation/Acoustics, Studio, Tutorial | No Comments »


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