Thursday, February 7, 2013

Plosives - A Background for Singers & Audio Engineers

Plosives are something that singers and audio engineers need to be concerned with. Well, especially audio engineers, although singers should understand the subject.

Basically, a plosive is like an explosion of air hitting a microphone during a recording process. Sing something like, "I'm on a Boat," with your hand about an inch in front of your mouth. Do you feel a sudden burst of air at some point? Try singing, "I'm on a plane." And then trying singing, "I'm in a car." Obviously, different sounds cause different amounts of that burst of air.

The worst sounds, ie. the ones that create the most significant plosives, are words that start with B's and P's. These are created by the lips. Nearly as bad are K and G sounds created by the body of the tongue. Also problematic are T's and D's, which are created by the tip (blade) of the tongue. And incidentally, some of those letters can be pronounced in different ways. For example, in English, the words "truck" and "the" both start with a T, but the T in "truck" causes more of a problem. I'm not entirely sure what the correct terminology for these different pronunciations is, but I personally call the sounds a "hard T" (in "truck") and a "soft T" (in "the"). I'm pretty sure those aren't the audiologically correct terms, but hopefully most people will understand what I mean.

All of the sounds that I mentioned above are caused by what are called the "stop consonants". That's because in order to make them, the flow of air through the mouth is temporarily stopped completely. In phonetic terms, this is also known as an "oral occlusive," a consonant in which the vocal tract is blocked so that all airflow ceases.

Are there other types of consonants besides stop consonants? Of course. "Fricatives" are partial occlusives which impede airflow in the vocal tract, but don't stop it entirely. And "nasals" are when the vocal tract is blocked, but air flows out the nose instead. Examples of nasals would be "m" or "n" sounds. Want to test those? Try placing your finger just under your nose and then say a phrase like "the bird flew over the lake." All of the sounds in that sentence can be produced in the mouth and vocal chords, and you don't need your nose. But if you try saying words like "motorway" or "nunnery" you're likely to feel some air coming out of your nose. It's faint, but it's there. Anyway, fricatives and nasals are not relevant to our intended topic for the day, so let's get back to plosives.

So why are plosives important? Well, as a singer gets closer to a microphone, the burst of air that comes out of the mouth will hit the microphone. Today's microphones are pretty sensitive. That burst of air hitting the microphone sounds different than the sound that should be hitting the microphone, namely the vibrating molecules that make a noise sound like it should. So instead of recording the proper sound, the microphone is partially recording the noise of air hitting the microphone, or essentially, a little wind-storm.

A secondary problem related to plosives is the fact that the closer a singer gets to a microphone, the better their voice sounds, in general. But as the singer gets closer, the plosives become more noticeable. A typical catch-22 situation.


So what is the solution? Well, I recommend that you try using a pop filter. Actually, every audio engineer will recommend that a pop filter the best solution for almost every vocal recording situation. But what is a pop filter? Well, it's a thin fabric similar to pantyhose, stretched over a frame. The pop filter is placed between the singer's mouth and the microphone, and it blocks the bursts of air from hitting the microphone, but the fabric is still thin enough that almost all of the sound of the vocalist come through (and you can boost the recording levels by a tiny amount to compensate, if necessary).

Here's a short thirty-second YouTube video to show you a pop filter:




Here are a couple of graphics that show what kind of difference you might see between a recording of a word without a pop filter (the first graphic), versus one with a pop filter (the bottom graphic). You can probably tell just from the visuals that the initial impact of the sound in the first recording is more harsh:






Now that you understand what plosives are, and how to reduce their impact with the use of a pop filter, it's time for further research. Tom Johnson writes a blog at I'd Rather Be Writing. He's got a post on it about plosives which is excellent because it has some accompanying sound files that help demonstrate what they can sound like. I'd recommend you check out his post, at this link:

Tom's Blog Post about Plosives


And finally, check out my Videos page on my main website to find detailed videos about a variety of music-related topics, from audio recording, to DJ'ing, to audio software, to music production, to music videos. Here's the link:

www.djbolivia.ca/videos.html





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