In the Elphel camera recording audio in sync with video is done by using Linux-compatible (since most USB devices do not require additional drivers they just need to be plugged in and are ready to go - so far all devices we tried worked out of the box) USB audio devices. These are widely available and range from simple thumb sticks with two 3.5mm jacks to multi channel recording devices with phantom powered XLR jacks.
Please note that the USB connector on the Elphel 353 cameras is USB 1.1 and therefore has a max. data throughput of 12 Mbit/s (~1.43 MB/s) and a maximum cable length of 3 meters (9.8 ft). If you think this data-rate is too low consider that an audio-CD (44100 Hz × 16 bits/sample × 2 channels) has a data-rate of 150 KiB/s which is roughly 10% of the available bandwidth.
The software and workflow to capture audio and video in sync is still in beta stage and a bit cumbersome.
The Elphel Wiki features a page with some more detailed audio hardware reports and instructions on how to get started with audio recording here.