Having the right kick drum sound is a deal breaker when it comes to making an amazing record. Would Led Zeppelin records sound as great as they do without John Bonham’s monstrous bottom end? Of course they wouldn’t. The bass drum is the pulse of the music. It needs to sound right, and that means it needs to be recorded right; all the editing, filters, and after effects in the world can’t save poorly recorded drums. The problem is that recording kick drums can be difficult.
Engineers have to keep three things in mind when they’re getting a bass drum sound: compression, microphone type/placement, and EQ.
When recording audio, the term “compression” refers to the process of narrowing the dynamic range of what you are recording by reducing the volume of the loudest sounds, without affecting the quieter sounds. Compression is used to reduce gain, and gain reduction is measured with a ratio. A ratio of 4:1 means that if the volume of what you are recording spikes, and exceeds the threshold you have set by 4 decibels, then the output will only be 1 decibel over the threshold. For example, if your threshold is set to 6db, and the signal you’re recording jumps to 10db, the compressor will bring it down to 7db for a gain reduction of 3db.
When recording kick drums, a good place to start is at a ratio of 10:1 and set the attack (the speed at which the compressor kicks in) at 7ms. From there you can start tweaking the settings until you find something you like. Make sure that the kick drum registers at least 5db on whatever you’re using as a gain reduction meter.
The best microphone for recording kick drums would be a dynamic microphone. These microphones don’t have the same sensitive frequency response that condenser microphones do, but they’re much more sturdy and stand up well against high-pressure sounds like kick drums and loud guitar amps.
However, if you don’t have a high-quality dynamic mic you can still get good results with some shrewd mic placement. What you do not want to do is place the mic directly in front of the kick drum’s beater, as this will end up giving you a dull and lifeless sound. If you displace the microphone a little bit, moving it off center, you will be able to capture natural resonance in addition to the general attack, and the resultant sound will be fuller. Having said that, you don’t want to move your recording device to far to the left or the right as each hit will sound too explosive. Experiment with mic placement. If you have the means and the time, you might even want to experiment with two microphones: one right inside the drum, and another placed outside of it.
When you’re EQing a bass drum track you want to concentrate on the three principal aspects of the sound: boom, smack, and click. The “boom” is the bottom-heavy thud that anchors the entire track. That thud can typically found in and around the 50-60Hz range. To boost the “Smack” that helps give more definition to individual hits on the kick drum, you want to start looking at around the 3-5kHz range. As for the “click”, this helps the bass drum sound to cut through the entire mix, and can be found close to the smack, at around 6-8kHz.
Keep in mind that these numbers are basic guides, and will vary according to the size and style of bass drum you’re using, and the particular sound you want.
After all, as is always the case when you’re in the studio, the recording process is both an art and science. There is always a level of subjectivity (either your personal taste or that of the client you’re recording) that comes into play.