How to measure your recording environment

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audiomike
Posts: 26
Joined: May 27th, 2016, 10:26 am
Location: Mid-Michigan

Post by audiomike » January 27th, 2021, 9:56 am

A common issue faced by anyone trying to record at home is background noise. We want to make it as quiet as possible. But just how quiet does it need to be and how do we find out what it is? If you're curious to know, there's an app for that. (I really hate that phrase) Decibel X is a free app for iOS and Android that uses your phone to measure SPL (Sound Pressure Level); the level of sound that your ears, and your microphone, actually hear.
If you're willing to put forth a little effort, here are the steps.

1 Prepare a few lines of text to read later.

2 Place your phone as close to your mic position as possible. Don't hold it in your hand or place it on a hard surface that can vibrate. Putting it on a small folded towel on a stack of books in front of the mic works well.

3 Open the app and watch the number on the bottom center of the screen while being as absolutely quiet as you can. If you get too close it will pick up your breathing.

4 The value will jump around a bit but hover around an average number. Write down that number. This is your background noise level, also referred to as Room Tone. (Don't use the app's AVG value shown in the lower left as it will be too high)

5 Start reading some text, at least a few lines, into the microphone as you normally would. The mic does not have to be turned on. When you're done, record the app's AVG value in the lower left.

6 Subtract the first number from the second. This Signal to Noise value represents the difference between your voice and the room's background noise level.

What does this all mean? I'm glad you asked. You want to get the background noise value to register below 30 dB if possible. This will usually translate to around -50 dB on Audacity's input meter.
In a good environment the difference between background noise and voice will be around 40 dB for someone speaking at average volume. Since everyone speaks at different levels this is not a strict number to use. Just be aware that you want the difference to be as large as possible.

So, now you can work on making your recording environment quieter and have a way to test and compare it with previous results. This is much better than just looking at how thick the squiggly line is in Audacity.
It's also handy to use the app once in a while just to see if anything has changed. You may not notice a difference in the background noise because your brain adjusts automatically and filters it out. But the microphone is much more diligent.

And before anyone brings it up in the comments, we're not concerned with whether or not the readings are accurate. We only care that they are done in a consistent manner. Using the same app on the same phone in the same way every time will yield usable results.

Good luck reader. This post will self-destruct in 5 seconds.

mightyfelix
LibriVox Admin Team
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Joined: August 7th, 2016, 6:39 pm

Post by mightyfelix » January 27th, 2021, 10:49 am

What a great idea! I can't wait to try it out. Thanks!

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