If you have it, use Audition to increase the volume and at the same time remove the room noise using noise removal. Simply use the sample from the 'room noise or ambient noise' recording you undoubtedly made. Maybe Soundbooth can do it too. For lectures, use a wireless lavalier in the future.
"what Harm said", but be realistic.
CSI-style sound restoration is a myth. Noise reduction and some careful EQ tweaking can improve the situation, but it's unlikley to "fix" it.
Proximity recording is the only way to go in a noisy environment. A minute spent on mic placement is an hour saved in post.
What they both said. I use Audition for most similar work, and with the Restoration>Noise Reduction, some judicious EQ and Filtering, can do pretty well. Live room "echo" is tough, but if one spends a lot of time working with the EQ and Filters, it can be reduced. Also, be careful with Noise Reduction as it can ADD "echo."
Now, here's something that might help, especially if you do not have Audition, or the time to do the work by hand in Audition - Magix has a little program, Audio Cleaning Lab, that is surprisingly good, and it's cheap too. I got this program in some bundle, installed it, and forgot it. I considered it to be a "toy," and I already had Audition and others for "serious" audio editing. One project was not going well. I was introducing more "stuff," than I was eliminating. In frustration, I launched ACL and ran the original file through it on the default settings - I was blown away at how well it did. With some fiddling, I got a great file! Teach me to jump to conclusions. For the few $'s that it costs, it has saved me plenty of time with similar bad recordings. I am still in awe of its power, and I think that I know Audition pretty well for video's audio cleanup. Might be worth a look.
Thanks all for the tips,
I dont have Audition.
Audio Cleaning Lab sounds useful, I also wonder if it will remove mic wind noise, a common problem so one would assume they have addressed it. Despite buying a Rode video mic and hairy cover, its as if it was not there, terrible racket at times :-(...if anything the inbuilt wind mic on setting was better but I need to test to confirm. Many recordings ruined unless this prog solves it.