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07 July 2011 @ 03:29 am
Tutorial: pops, pop screens and equalizing  
Hello again!

Here's the tutorial about removing pops that I promised you.

First of all, a disclaimer: I'm not at all an expert in things relating to sound editing. I'm fumbling my way through this and I came across this method by trial and error, so I'm not claiming this is the definite answer, or anything. And I'll be very happy to learn if there's a better way to do things out there!

There are two things I'm proposing in this tutorial: A. build a pop screen to try to minimize the amount of pops you record, at the source and B. use the equalizer tool to remove the rest.

This tutorial was created using Audacity 1.3 (Beta).

1. What's a pop?

First of all, what do I call a pop? It's the loud noise created by too much air being blown into your mic. I'm sure if you're doing podfic you've encountered that problem, especially in sentences with P or « SH » sounds. If you're too close to the mic or speak with too much energy, you get those unpleasant sounds in your recording.

I recorded a sample, trying to create pops on purpose (please ignore the buzzing - I left the computer plugged in when I recorded and it interfered. The best way to "experience" the pops is to use headphones and turn up the volume):

Pops tutorial - without pop screen by greedy_dancer

I usually listen to podfic with headphones on the public transport, which means that I have the volume turned to the max. And such an influx of sound in my ears is likely to make me startle, at best, and cry out, at worst. On top of that, I just find them very distracting when listening to a story! Therefore I try my best to avoid them when I record.

2. Pop screens

Now, the way I dealt with pops in the beginning was simply to re-record every sentence or word in which I found a pop, and that honestly got old REALLY QUICKLY.

Then I tried to build a pop screen (also called pop filters or pop shields, Wikipedia tells me).

A pop screen is the thing you see in front of recording artists in studios:

It prevents the air from hitting the microphone at full strength, while still letting the sound through.

You can buy pop screens, of course, but since I'm cheap – and always find myself recording podfic in the middle of the night – I decided to make one myself.

At first what I did was tie a paper tissue on top of my microphone, trying to make it puff so there would be a sort of “bubble” around the head of the mic. That worked ok, but pops were still getting through and frustrating me.

There are multiple tutorials out there on how to build your own pop screen. For example this one uses an embroidery circle and nylon tights.

I didn't have an embroidery circle at home, so I looked around and found a metal circle that used to be a necklace. You know, one of these:

I taped the end shut and shoved it inside an old tight, then put another old tight on top of that for extra filtering power!

I'm quite happy with it, but I still have to find a better stand for it. At the moment, it's half a plastic bottle, two cuts at the side to slide the screen in, and some lentils at the bottom to weigh it down and make it stable.

I find that the screen is most effective when placed closer to my mouth than to the mic, so the final setup looks something like this:

This is what the sample sentence sounds like when recorded at exactly the same distance and same volume, but with my pop filter in place:

Pops tutorial - with pop screen by greedy_dancer

As you can hear, that actually got rid of all the pops here... So using a pop screen is definitely a great step towards a pop-free life.

However, the last time I was editing, I found minor pops in my recordings still. This is where the equalizer comes into play.

3. Using the equalizer tool

According to Wikipedia, equalizing is the process of adjusting the balance between frequency components within an electronic signal. Hm. What I understand from it is that it's a way to modify how loudly you hear certain frequences in your recording.

If you look at the Equalizer in Audacity 1.3 (and here I should also say that I'm using the French language version, so I'm basically trying to guess what it says in English – I don't think I'll be too far off though) you see this:

Here I circled the dBs in blue (the higher the dBs, the louder the sound) and the frequencies in yellow (the lower the frequency, the deeper the sound). So what this tool allows you to do is decide how much of a specific frequency you want to hear in all or part of your recording. Presumably, if you were able to determine the precise frequency of a continuous shrill sound on your recording, you could get rid of it by just « muting » this precise frequency with the equalizer.

Now you can see that you can select pre-set curves. On my version I have options for "telephone", "bass cut", "bass boost" etc. Looking at those curves should give you an idea of what they do (cut or emphasize certain frequencies). None of these did what I wanted, though.

Thus, what I did was create a custom curve to apply to my pops. This curve was, quite frankly, worked out arbitrarily. I would encourage you to work out what's best for your recordings, according to your setup, environment etc. Trial and error is the way to go!

The curve is created by using the mouse to click on the green line. Clicking creates a white dot. If you click twice at different points of the line, you can start bending the portion of the line between the dots as you see fit. It takes a bit of patience at first but you should get the hang of it easily, and then the sky's your limit!

I wonder what this one would sound like?? *g*

This is what my actual custom curve looks like:

Once I had created this curve, I saved it to the preset curves and named it "pop remover" so I would know it immediately.

Now, let's see what it does!

I used the 1st sample posted in the tutorial – no pop screen – because it provides the most dramatic example. This is what it looks like, before and after I applied the filter:

You can see that the curves are way smoother already.

And this is what it sounds like, once I've applied my « pop remover » filter to the whole thing:

Pops tutorial - without pop screen + equalizer by greedy_dancer "s

Now, this was a really extreme example, which is why the custom filter I created was not "strong" enough to get rid of everything, even though it's already much better.

It is enough to get rid of pops I get while using the pop filter, though. In that case, instead of selecting the whole audio like I did just now, I just select the smallest possible bit of audio where I can hear the pop and put it through the filter by clicking Effects > Equalizer > selecting my "pop remover" filter > OK, and repeating as needed throughout the editing process.

Now, if you have to deal with extra strong pops like in my sample, you can always modify the custom curve! I changed mine slightly, like so:

And this is what the sample sentence sounds like then:

Pops tutorial - without pop screen + stronger equalize by greedy_dancer

You can definitely hear that there's much less bass in the recording, but the pops have disappeared! And since this is what I set out to do with the tutorial, I'm calling it a success - and a night! I wish I hadn't edited the less obvious pops out of my recordings already, because this is not very subtle and the result is not great quality. However, I guarantee that it gives great results on less noticeable - but still annoying - pops!

This concludes this tutorial. I hope you found it useful or at least that it gave you some hints on where to start your own explorations! Please let me know if something wasn't clear, and if you have questions I'll do my best to answer them.
twasadarktwasadark on July 7th, 2011 04:08 am (UTC)
WOW! This is awesome! Thank you so much for all this work! My next podfic will benefit from it. :-)
the slashy side of me ...: Podficgreedy_dancer on July 7th, 2011 11:46 am (UTC)
I'm glad you found it clear and useful! Thanks! :)
hardboiledbaby: music ipodhardboiledbaby on July 7th, 2011 06:36 am (UTC)
This is great! I tried using the equalizer once, but didn't really know how to tweak it to get good results. Will definitely try this, thank you!
the slashy side of me ...: Podficgreedy_dancer on July 7th, 2011 11:47 am (UTC)
Thank you! I actually stumbled on this totally by mistaze while trying to "smoothe" the overall volume of the thing I was working on, but then I spent most of my evening merrily going through all my WIPs and getting rid of all my pops everywhere! \o/

Good luck with your projects! :)
(Deleted comment)
the slashy side of me ...greedy_dancer on July 8th, 2011 01:08 pm (UTC)
Thanks! I hope you find it useful! :)
lunate8lunate8 on July 7th, 2011 07:07 pm (UTC)
Very cool -- thanks for all the visual aids and audio examples!
the slashy side of me ...greedy_dancer on July 8th, 2011 01:09 pm (UTC)
Thank you! :)
(Deleted comment)
the slashy side of me ...greedy_dancer on July 8th, 2011 01:11 pm (UTC)
Haha, thank you! I'm not sure I should take that as a compliment, but I will! :p

I have a bigger laptop that's old and whiny, and I find myself using it less and less these days... Just the noise of the fan irritates me. It also means I can't record on it, so I usually record on the netbook.
(Deleted comment)
the slashy side of me ...greedy_dancer on July 15th, 2011 11:17 am (UTC)
I'm glad you found it useful!! :D
elaineofshalott on February 7th, 2012 10:40 pm (UTC)
Oooh, thanks! I had to remove some loud f-noises (don't know what they're called) from my latest (hur hur, really my second ever) recording and that equalizer tool was very helpful! Yay podfic_tips!