Ask yourself if this has ever happened to you. You are waiting for the bass player to arrive. You have a DI and perhaps a mic ready for his bass guitar and amp. The door opens and instead of a human figure you see a huge brown form enter—the bottom end of an acoustic bass with a menacing steel end pin sticking out, sometimes filed to a sharp point! Oh no! How the heck am I gonna deal with this thing?!
The acoustic bass is an instrument that strikes fear in the hearts of some recording engineers. Well, rest easy, my friends, you just need to go to your happy place and find your center. Forget much of what you know about recording the electric bass and prepare to start on a new journey.
Usually an acoustic bass will arrive at your studio equipped with some kind of pickup and a 1/4" jack. These pickups are almost always acoustic, rather than electromagnetic. They pick up the sound vibrations directly from the wooden bridge of the instrument. (This would be like recording your vocals by sticking a U47 mic directly into your larynx. Gag!)
You can, and should, plug this signal into your usual bass direct box and record it to its own separate track. See, sometimes the sound from this pickup will sound great. But usually it will sound like, well, not so great; dark and boomy with a complete lack of highs, or honky and nasal with no lows. The interesting thing is that I find the pickups which advertise a completely flat response are the ones that sound the worst all by themselves.
However, many really great jazz bass players use this kind of a pickup and a pretty small amp just to add a bit more bottom end to their acoustic sound. Since you are hearing the acoustic output from the instrument plus the amplified sound from the pickup, this approach can be made to sound very good to a listener in the room. In the studio you want to take a similar approach, isolating the bass in its own room and adding a mic to the direct sound from the pickup.
No, I don’t want to stick it anywhere near your f hole!
As a young engineer I kept running into bass players who were obsessed with something they called the “f hole”—so compulsive that at first I was afraid to ask what it was. I was relieved to learn that these were merely the two holes in the front of the bass. They are shaped like a cursive letter “f”. These bassists would insist that the very best sound is obtained by placing a mic right up on one of the f holes, and they usually had a preference for one or the other. I quickly learned that the sound coming out at that point is very dark and mushy, much like the sound of some of those pickups.
Once I was older and more experienced I found the courage and diplomatic skill to distract the bassist just long enough to place a large-diaphragm condenser mic directly in front of and about six inches from the strings, with the capsule halfway between the bridge and the bottom end of the fingerboard. Stick your good ear down there and have the guy play. Move your ear around and you will easily locate a good sound. When you find the spot, put your mic right there. Promise the player whatever amount of money or beer it is going to take to get him to stay still. Any movement at all will alter the sound, and not in your favor if you got your mic placement just right in the first place.
One of the classic old-school mic choices for this technique is a Neumann U47 in the cardioid position, but many cheaper large-diaphragm condenser cardioids will sound great (see Figure 1). As a general rule you want to record bass instruments with a brighter sounding mic, and treble instruments with a darker sounding mic. So pick a mic with some zing in the mid-highs, perhaps that mic that you keep trying on vocals but always sounds too edgy. Record this mic to a separate track.
Getting rude with the packing foam
Now I am going to reveal to you one of my most guarded secrets: Placing a mic in such a way that the bassist can dance around, spin the instrument, turn it upside down, whatever, and the sound will not change. Grab a hunk of packing foam. I have used the nice blue stuff that comes out of a Sennheiser MD421 box. Carefully wrap that foam around a small-diaphragm omnidirectional condenser mic. I use a very expensive Sennheiser MKH800 but you can use any good omni, ’cause you are gonna do some significant eq to it anyway. Try a Neumann KM183, Shure SM80, or perhaps a Shure KSM141 in the omnidirectional pattern.
Now ask the bassist to take a deep breath and try to relax (or better yet to close his eyes and not look), and then gently slide that foam-wrapped mic up into the hole between the bridge and the body so that the capsule ends up two or three inches above the top of the bridge, as shown in Figure 2. Make sure the mic is not going to slip and adjust the foam if necessary. Give the still-unplugged mic cable a few turns around the tailpiece to secure it, and then plug it in to the mic. Have the bassist play a bit and make sure the cable is not audibly vibrating against the body of the bass.
Do not be afraid to dump a bunch of bass from this mic with a low-shelf eq or even a highpass filter. I also boost a healthy 4 to 6 dB around 3 kHz to add some air and definition. It is very important to look at your waveforms after recording and line up the waveforms from the mic and pickup, reversing the polarity (phase) of the pickup if necessary to make sure the two signals are not working against each other. You can also add another mic up higher, pointing near the player’s left hand on the fingerboard. This mic will help to add further definition, as shown in Figure 3.
Putting it all together
So now you have two or three tracks of bass: pickup, plus foam-wrapped mic or stationary mic, or maybe all three. There’s a great sound in there somewhere!
My approach is to first decide which of the two or three signals sounds best all by itself. Then I start adding little bits of the other signals until I get what I want. For me this usually ends up being my bridge foam-wrapped mic with a bit of pickup added in for extended low end. I’ll usually dump some low end from the whole combination to give the bass more definition in the mix.
Experiment with some beefy compression, maybe 6 dB of gain reduction at 3:1 with a medium-slow attack time, perhaps 50 milliseconds. Release time might be 50 to as much as 150 milliseconds, but you can do this in the mix and take your time to experiment. The important thing is that by recording two or three different signals you have some options!
Michael Schulze is a recording engineer and faculty member at the Lamont School Of Music at the University of Denver. As demonstrated in his 3-part series on guitar amp miking (January–March 2006), he has this thing about sticking mics where you wouldn’t think they’d fit.