Sound is commonly seen as a sine wave or “Sound wave”. A sound wave, like most other waves, has crests and troughs, which can fluctuate. The more extreme a waves crests and troughs, the louder the sound will be, and vice-versa. The way we measure the amount of hight a crest or trough has is through Decibels. Decibels, simply put, are how loud you hear the sound.
So, simply put, the more extreme a sound wave is, the louder it is. If your music is too loud, often you will limit the volume.
But, say only a portion of your music is too loud, and limiting the volume will make the rest of the song almost inaudible.
Fear not, there is an easy solution to this; Compression. Compression is both an analog and digital effect that limits a sound wave ONLY if it passes a certain decibel amount, which is set by the user of the effect. Compression has 3 main setting, Threshold, Ratio, and ‘Attack’.
Threshold is the amount of dB (Decibels) it takes for the Compression to start limiting. Say, for instance, most of your song is at 3dB, but at one point it spikes to 10dB. This is an extreme spike that could sound really unflattering, and that 10dB you want to be equal to the rest of the track. since the rest of the track is 3dB, the Threshold of the Compression should be set at 3dB. Simply put: the Compression will now only effect anything that spikes beyond 3 Decibels, anything that lies below 3dB will remained unchanged.
Once you have the Threshold set, then you go on to Ratio. Ratio is how much the Compression lowers the volume, or ‘Compresses’ the wave. Going back to our previous situation, you now have your Threshold set to 3dB, if you want to limit everything strictly to 3dB, then you want a high Ratio (10:1 ratio is considered extremely high). but say you only want everything to be close to 3dB, a 1:2 ratio would probably be preferred. The Ratio represents how much of the original volume will be retained. Simply Put: IF the volume exceeds 3dB, the Compressor will cut 1:2 of the original volume.
After you have Threshold and Ratio set, the last basic setting is ‘Attack’. Attack in Compression means how fast the Compressor will react to something spiking beyond the set Threshold. This is usually measured on a scale from 0.1 seconds, up to 5 seconds. Setting the Attack at a high speed (0.1 seconds) will often result in a “Punchy” sound, where the initial sound of a note may be very loud, but the rest of the note is quiet, say your music quickly goes to 10dB after being at 3dB, you probably want to set Attack at 0.1 seconds to promptly reduce the volume of the loud bit of music. Simply Put: IF the volume exceeds 3dB, the Compressor will cut 1:2 of the original volume in 0.1 Seconds.
You can use compression for many things; when mixing a song where the guitar part gets too loud only in a certain part, when peoples voices in a recording that are not of proportionate volume, and even adding a ‘punchy’ sound to bass guitars or drums. The best way to master the tools of Compression is through experience, so I encourage you to mess around with Compression on your recording software to get the hang of how it works.