The major problem I find when mixing a song is the overall volume of the bass guitar. When they're playing on the lower strings, you can hear everything clear and full, but when they're playing on the higher strings, things tend to thin out and sound quieter. So how do we fix this problem? Well, besides riding the track fader with volume automation, compression is a major tool in fixing this. A lot of it has to do with where the threshold is placed and the attack time. If your threshold is too high, then you won't be able to compress the more average notes and only get the loud notes. If your threshold is too low, you may compress the loud notes way too much. So how do you do it you may ask? Well, this is how I personally compressed bass guitar.
I first find my average level, and I put my threshold to where the average level is getting about 3 to 6 dB of compression. My attack time is generally around 1 ms. This gives me a nice, fast attack but still allows a small bit of transient information to come through. If you want more transient attack to come through, then a longer attack of maybe 15-20 ms would be best for you. My release time is usually between 300 and 500 milliseconds. This allows the note to fully fade away for most instances before the compression goes away. The ratios I tend to use usually fall between 4:1 and 6:1. It gives a nice amount of compression, but not too crushing.
So with the threshold giving around 3 to 6 db of compression to the average volume of the bass, my louder hits are going to have somewhere between 6 and 10 db of reduction, and my quieter hits will not have any. What this will do is compress my average down a little bit and, of course, the loudest notes lowered even more. So what should be happening is that everything is coming closer to the volume of the quieter parts. If you were to record through this setting, you would see that your very dynamic loud to soft bass waveforms are now a lot more uniform. Not really a rectangle, but more in the same general ballpark of overall volume. This will allow the bass guitar to stay at a steady volume in the mix so that the instrument does not get covered by the guitars.
This technique will not change the overall low end of your track though, because the lower strings have more natural bass resonance than the higher strings. What you can do, however, is to add a bass roll off (HPF) filter around 80 Hz. This will take away some of the overall big bottom end, and the kick drum is really going to be down in that area anyway, so we're trying to keep our bass guitar and kick drum away from each other to have them more defined as individual instruments. If I really need the dynamics to be gone completely from my bass guitar, say that I am mixing a metal band, then I will move my attack time even faster than 1 ms and bring it down to around 500 ns and move my ratio up to a limiting threshold where it's higher than 10:1; usually I'm around 30:1 (if not 100:1), effectively making it a brick wall limiter. Now, remember, when you are using extremely fast attack times you must also have a longer release time or else you will have distortion on your bass guitar, which you probably don't want to have.
So that's how I do it. I generally use a soft knee compressor like the Waves Rcomp or the CLA1176 compressor on my bass tracks, but really any compressor will do the job if you set it up correctly. Just experiment with the attack and threshold while maintaining average ratios and release times and see what you can come up with on your own. Most of the fun of mixing is trying out ideas and figuring out ways of making things sound even better than they actually are!
Well, that's it for now. Don't forget that you are welcome to stop by and tour our facilities anytime. Just give us a call at 859-335-8440 (if you're local) or TOLL FREE at 877-335-8440 to set it up, so we can give you the ultimate LIRCo experience. See ya next time!!!
Head Engineer, LIRS