Well, I've been slogging along with teaching myself audio. I haven't had any formal training and no friends that are audio technicians so it's been a bit of trial and error and error, though I am making some correlations. I don't know if this is helpful to anyone but myself and other fledgling photographers poking their lenses into the strange world of audio, but here goes:
ISO = GAIN
ISO in photography is a number which measures the sensitivity of the recording medium to light. The higher the ISO, the more sensitive to light and the lower light you can shoot in and get a usable image. ISO 1600, for example, is considered a high ISO (50 ISO is low) and can be used to shoot at night with a fast lens.
Audio gain, is similar. The higher the GAIN setting the more sensitive the mic is to picking up sound. So if the signal is weak, you can increase the gain to capture the sound, just as if the environment is dark, you can increase the ISO to capture the light.
However, you don't get something for nothing. As you increase ISO, you get "noise" in your image, which appears like weird discolored pixels in the shadows. As you increase GAIN, you also get "noise" which sounds like hiss or crackling in your sound.
RAW = WAV
In digital photography, the "negative" is a RAW file. It is the raw unadulterated data collected by a camera. It is typically a large file, but with it you can control exposure, color balance, etc.,
In digital audio, the WAV file is the equivalent of a RAW file. You can manipulate a WAV in post-processing just like you can a RAW file in Photoshop.
MP3 is to audio like JPG is to photography. Both are compressed formats that lose information and don't offer the editing possibilities that RAW/WAV files do.
Another interesting corollary is the waveform and the histogram. Both the shape of a waveform and histogram tell you about the image. A waveform where the form hits the ceiling is similar to a histogram where the highlights are clipped. They both represent lost information that can't be retrieved.
Interestingly, just as it is better to err on the side of underexposure in photography, it is also better to record with lower levels in audio. You can always bring out details in the shadowy part of an image or the quiet part of a recording, but you can't recover highlights or where the waveform has clipped.
Levels = Correct Exposure
To "monitor levels" in sound is to make sure that your'e not clipping your audio, that the mic sensitivity is set so you can capture a good range of sound without clipping loud sounds. Similarly, in photography, you monitor your exposure so you get a shot where there is detail in the shadows and you don't blow your highlights.
In sound, level monitoring is done by watching a light ladder or some kind of visual representation of the loudness of the sound. In photography it is done by peaking at the histogram and making sure the histogram doesn't slide off the left or the right.
more to come as I figure things out....