The game is recorded on an iRiver 800 that has 256MB storage capacity. When set to record in stereo at 44 kHz at 128 kbps, that's enough for about 4 hours 30 minutes of recording. A Sony stereo microphone (ECM-DS30P) is plugged into the line-in port.
The MP3 file is copied to my Mac, then loaded into Audacity (currently 1.3.9). I apply the Noise Reduction filter (using a sample of the ambient room noise), then 6:1 compression, then either 6 or 12dB amplification (sometimes 15dB when the recorder battery was low). The file is then exported as an MP3 file at 64 kbps bitrate (80 kbps for Masks, there were some bad artifacts in the introductory audio when I exported at 64 kbps).
Note that because the iRiver Music Manager does not run on Lion, I still run Snow Leopard (10.6.8).
The voiceovers for Realm of Shadows, Colymar, Serenity, Adventure! Serial 2, Masks of Nyarlathotep, Day of the Beast, and The Haunting were put together using GarageBand with me recording the main audio track. The intro to Adventure! Serial 1 was pieced together from snippets of the pre-adventure hooks which were recorded and edited with Audacity, then placed into GarageBand. In all cases the final audio was then sent to iTunes. All of the sound effects and music were from GarageBand.
One of the players has purchased a Zoom H-2, which we'll use in tandem (for near side-by-side comparisons). If the Zoom produces better quality audio, then I may consider purchasing one of my own. Also, given the release of Mountain Lion (10.8), Snow Leopard is going to become obsolete.