When selecting a preamp for the SM7 for voice-over work, make certain the preamp has a minimum 60 dB of gain.
Here's why:
- With an acoustic input of 84dBSPL - typical speech level at 3 inches, the output level of the SM7 is -69dBV.
- The mic preamp must increase the mic signal level up to about 0dBV - line level.
- -69dBV of mic signal, increased by +60dB of preamp gain, equals an output level of -9 dBV. Not quite to the 0 dBV level, but close enough to work with most line level inputs.
Many modern mic preamps assume the mic is a condenser mic with a "hot" output level. Thus, it is common to find mic preamps or mic mixers with gains of only 40 to 50 dB. This is not enough gain to bring the SM7 signal up to line level. One example of a mic preamp with sufficient gain: Grace M101; www.gracedesign.com. Or the Radio Design Labs model HR-MP2A; www.rdlnet.com.
If your interface/preamp does not have enough gain, you can add a phantom powered preamp in-between the SM7B and your interface. The sE DM1 phantom-powered preamp or Cloudlifter phantom-powered preamp adds 25-28 dB of additional gain.
There is a superb USB mic preamp with sufficient gain from Sound Devices: USB Pre 2; www.sounddevices.com.
In June 2012, an online site that reviews pro audio products recommended the following preamps/interfaces for the SM7:
M-Audio Fast Track C400
Focusrite Scarlett 8i6
