When digitally recording an interview there are several options regarding what technology to use.
Digital Recorders such as a Zoom H1, Zoom H2, and Edirol R-09 have excellent built in internal microphones designed to record without the use of an external microphone. These standalone units are compact and easy to use and have adequate storage capacity.
Digital recording units such as a Marantz Professional Solid State Recorder 671 ideally require a quality external microphone with a built in pre-amp, cable and stand or a lapel microphone with wireless set up.
Another portable recording method is to use a USB microphone with a laptop and sound editing software. This may save time on transferring files but will still requires a laptop with a good soundcard, adequate memory and storage space for real time digitization. Regardless of the equipment the most important requirement of any digital recording device is a way to monitor the specified strength the signal input level (voice).