Practical audio theory – Masking
Let’s talk about the ‘I can’t hear you because of all that noise!’-syndrome, also known as masking
You will probably know a situation like this. You are in a pub with some friends. One of them is talking, but someone else has something to add to that. And it’s kind of urgent. So she doesn’t wait to talk until the other one has finished speaking, but starts talking immediately.
The other person isn’t very happy with that, so he increases the volume of his voice a bit. And before you know it, they are in the middle of some kind of contest who can talk the loudest. Because if you keep talking at the same volume, nobody will hear you anymore. Well, that is called masking. One person masks the speech of the other.
Masking happens when two sounds are in approximately the same frequency range. Something to keep in mind when mixing.
Practical example: the frequencies that provide intelligibility in a vocal or voice-over recording are between 2 and 6 kHz. As you can see in the frequency overview in the part Hz, kHz, Frequencies…What? an electric guitar also has a peak in about that same range. It overlaps. So an electric guitar will mask the vocal track very quickly, you don’t even have to turn it up very loud. A bass guitar will eventually also mask the vocals, but you’ll have to turn it up much louder before that happens.
If you try to mix a voice-over/vocal track with music track that happens to contain a lot of electric guitar, you’ll notice you will have to turn it down a lot to make sure it doesn’t get in the way. But if you know that the problem is mainly between 2 and 6 kHz, it’s much better to grab an equalizer and just turn back those frequencies a bit in the guitar track. If you then add these same frequencies a little in the vocals/voice-over, you have reduced the masking effect even more. And now you can turn up that guitar track, so it will have the impact you want it to have!