Updated: Oct 25, 2021
Using a compressor to turn up the bottom end volume
So, we all know what compression is right? Gosh, I trust you do. If you don't, go learn. Its not hard to understand. Its even easier to understand what offside is in football (soccer). But to answer in brief, compression is bringing down the loudest parts of any recording at a certain level (threshold), while retaining the loudness of the parts below that threshold. That's as simple as it gets and the effects can be tremendous. The effects can also be complicated by what you need to do with the compression. That's a topic that I encourage you to study on your own time. Here however, I'm going to show you something really cool.
Lets go to the equalizer Bob...
Ok, so if you ever remember the equalizer knobs you found on old stereo systems. You know the ones. A bunch of slider bars that go up and down designed to enhance the bass or lower the treble or punch up the mid tones? If not, here's an example:
I still have mine from the 80s. Works quite well too. I remember adjusting the knobs until the display in the center was right were I wanted it. Problem is, I knew nothing about EQ (still don't). However, I want to use this as an example. Each knob is a different frequency of sound and by moving them up and down, you can boost or cut those frequencies.
Huh? Wait. Weren't we going to talk about compression?
Yeah, I'm getting to that. Much like how an equalizer works in principle, a compressor does the same. Well, not on frequencies. Rather on loudness. Lets take our equalizer and reduce all the frequencies above 2khz. Do this in a linear form (progressively and equally down to 0). You wind up making those frequencies lower. Lets say you do the opposite from 100hz to 1khz in the same linear fashion. You've boosted the low end.
Compression can do the same. We use a compressor to gradually and equally lower the volume (dBm) from a threshold, usually some -dBm number; say starting at -15dBm. At that point there is no change in the volume from -15dBm down to -Infinite dBm. Above that, the volume gradually lowers relative to the amount of compression applied. Lets say, based on our settings, we want the loudest part (-3dBm) to become -6dBm. We can do that with compression.
But a really cool thing can be done if we need. Lets go back to our equalizer example. What if we decided that anything quieter than -15dBm we wanted louder? What if we were to reverse the compression at that point so that say, a -40dBm were to become a -30dBm and so forth until the volume reached -15dBm. We can do that! And a lot of compressors you might find or use in your Digital Audio Workstation (DAW) might have a handy way of doing this called makeup gain. That means that if the lower parts are too quiet, the compressor will automatically increase the volumes.
If you have a nice, neat graphical compressor like the General Dynamics compressor found in Reaper DAW, you can really create some awesome and customized compressions.
This is the default for the General Dynamics compressor. See the dark and lighter areas. The lighter area is where the compressor will be affecting the volume. Here, there is no compression going on. Input equals output.
Here is the same compressor but with compression starting at a certain point. Note that the compression is linear in this example. The General Dynamics compressor can create a varied compression ratio if you really want to get creative. But for here, this is sufficient.
In this example, not only is the volume above the threshold decreased, but the area below the threshold is increased as noted by the red line. Those areas are boosted, much like boosting the lower frequencies on the equalizers.
Now lets get silly crazy for a moment. What if we didn't want any top end compression-above a threshold but wanted anything below that threshold amped up? We can do that! If you see where that bend is, anything below (to the left) will be increased in volume.
We might also call this one makeup gain.
And here's another neat trick this compressor can do. It can act as a gate. A gate is either software or hardware that cuts all volumes below a certain level. Its very handy to use if you have a lot of annoying background sounds. Once the input volume goes below that bend, it drops like a brick to nothing. As you can also tell, there is a slight angle to it much like the other examples, so you can really dial in what you want this effect to do.
Cool. I guess. So what next?
I know. A lot to take in and I hope you can find a compressor like this. I do use Reaper DAW and if you have this type compressor, you can certainly see how this can change your approach to compression.
To know more about this compressor, you can visit Kenny Gioia on Youtube and watch his video on the General Dynamics compressor here.
Until next time, happy engineering!