It is important to have a reliable digital recorder as part of your ghost hunting equipment kit. The TOS team uses this digital dictaphone to record a backup of all audio during our investigations to capture potential electronic voice recordings (EVP).
You need to find a one that records in stereo (preferably with external inputs for microphones). It also needs to use a 96 Kbps or greater sample rate , ideally save files in a non-compressed format such as WAV files and use a 24 bit analog to digital conversion system.
If you are interested, you can read more in this past TOS article for additional tips and tricks for EVPs.