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 (or Mountain Lion or Mavericks), I still run Snow Leopard (10.6.8).
The voiceovers for The Flood, 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 H2, 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 (more likely an H2N). Also, given the release of Mavericks (10.9), Snow Leopard is likely going to become obsolete.