Sort of "reverse" question

[Battlespeed]

I need to record something fairly long (20 minutes) that needs a certain background ambience, namely lecturing to a college class or speaking to a business group. This means finding a soundtrack that has ambient sounds that an audience would make (a bit of echo, occasional coughing, etc.). I have the applause track to add to the end.

Does anyone have any ideas where I might find such an audio sample that's long enough so that any required looping wouldn't be obvious?

TIA!

[Scott Pollak]

The short answer to your question is no, I don't know where you'll find 20 minutes of such ambience. Most decent SFX libraries will give you a couple of minutes at best.

The best way to do this is to take any and all similar ambiences that they offer, for example, if they have 4 different sfx of 'lecture hall ambience', grab those. Also look for something else that may sound similar such as 'library ambience' or 'quiet office ambience'.

Lay them all out in your audio editor and vary them, for example, lay sample #1 one of the lecture hall ambience down then fade it into sample #3 of the office ambience then sample #1 of the library ambience and so on. If you do this enough and vary it, and do imperceptible crossfades from one to the next AND if you have some sort of narrative going on over it, no one will ever notice.

[Battlespeed]

The short answer to your question is no, I don't know where you'll find 20 minutes of such ambience. Most decent SFX libraries will give you a couple of minutes at best.

The best way to do this is to take any and all similar ambiences that they offer, for example, if they have 4 different sfx of 'lecture hall ambience', grab those. Also look for something else that may sound similar such as 'library ambience' or 'quiet office ambience'.

Lay them all out in your audio editor and vary them, for example, lay sample # one of the lecture hall ambience down then fade it into sample #3 of the office ambience then sample #1 of the library ambience and so on. If you do this enough and vary it, and do imperceptible crossfades from one to the next AND if you have some sort of narrative going on over it, no one will ever notice.

Thanks very much for your thoughtful answer, Scott. I'll do exactly as you recommend!

[Mike Sommer]

Other then looping some off the shelf Sound FX, this might be the time to get a portable recorder and make your own custom SFX. Some things that people don't think about, is the general sounds that are apart of a building like the sound of an air conditioner (you can make this yourself if you have forced AC), distant phone rings, squeaking chairs, rustling of paper and the like. But you'll be surprised at how little ambient noise you'll need.