These days, the upright bass is not just used in jazz, classical, rockabilly, and country music.
It's everywhere from roots rock to hipster lounge to salsa. It's also known by many names: double bass, contrabass, bass violin, bass fiddle, string bass, and, thanks to some Wikipedia research, bull fiddle. Whatever it's called, however, you'll likely be recording this beast someday, and here are some tips for capturing the instrument's ballsy tones.
The upright bass is a big acoustic instrument, but you don't need to be a physicist to get the best sound out of it. Before you start placing mics, listen to the player, evaluate the song being played, and assess the overall sonic arrangement. Remember, you're not just splashing bass frequencies on a track, you're documenting a player's technique, phrasing, and performance dynamics in the service of a musical work.
The Single Mic Approach
A good starting point--from engineer Scott Sedillo who used the technique to record Carlitos Puerto for a Zane Musa session at Straight Ahead Records--is one mic near the player's plucking hand. Sedillo used a Neumann U47, but experiment with any large-diaphragm condenser. He placed the U47 back about 12" to 14" from the strings to get a good pluck sound, as well as some roundness and depth. For this session, Puerto was isolated a bit from the rest of the band, and some mover's blankets were affixed to the wall behind him for a bit of sound absorption. Obviously, you have to take care to ensure other instruments don't bleed into your bass sound too much, but, as always, experimenting with what works best for you, the song, and the performance is the best way to determine isolation and sound absorption/diffusion needs.
In this example, we have the great John Heard--truly one of the greats of jazz bass. Heard was tracking The Jazz Composers Songbook at Straight Ahead Records, and Sedillo wanted to put up a second mic to capture the many nuances of Heard's playing. In addition to the U47, Sedillo wrapped a Schoeps mic in foam (which not only held the mic in place, but functioned as a shockmount"), and placed it inside the bridge. This dual-mic setup delivered such a great sound that no outboard compression was used down the line. Everything just fit together, and it sounded as if the listener was sitting right next to Heard at a club date. The session was live, so Heard was isolated a bit with gobos, but the setup still allowed him to maintain sight lines with the band to ensure good interplay between the musicians.
In another instance, I encountered a bowed upright bass. The player already had a transducer mic in the instrument. While these setups don't hear" the way a microphone does, the sound worked for me because it was for an alternative rock recording. I ran the signal through some compression for added character and gain. I also set up a Rde K2 large-diaphragm condenser in a wide cardioid pattern, and, believe it or not, added some reverb, as well. The result was perfect for the recording. As I say often, any mic works that works for the song. You can't go wrong if you start by standing around the instrument, and listening to the player play.