firstblood20:

Sound Ambiance and Effects

• TabletopAudio’s Soundboard – online and easy to manage.
• It’s main site contains great 10 min looping pieces based on locations to use as background sound.
• Ambient Mixer – Similar to the previous, it provides custom combinations of different effects (steps, chatter, wind) to create different classical settings for a fantasy adventure.
• Check also this list within that site, focused on caves.
• Syrinscape – The product that is trying to be the big daddy of gaming soundboards. It provides both ambiance and effects, and differentiates itself by allowing you to pre-set the sounds for each part of the story. It requires to be downloaded, and works through paid content packages, though it has a free trial. It aims to soon cover all major operating systems.
• Soundboard.com – User generated collections of sounds. You can register and make you own. Oddly, the pop-up panel doesn’t have loop or stop options.
• Here’s another one from there focused on attacks and doors.

Music Scores

• Movie sound tracks –  Conan is very often recommended. Also, Lord of the Rings.
• The music from games like Neverwinter Nights, Baldur’s Gate, Bastion, and Might and Magic (I-VIII)
• A list of other candidates, from the Gnome Stew blog.
• A Reddit aggregation of themed Spotify playlists for D&D.

Using These

• Music should be without vocals and unobtrusive, including in volume. Even if the score feels epic, avoid bringing it to the forefront of the moment, as D&D is a spoken game.
• Make sure you quickly pick and separate the tracks you are going to use before the game, so you don’t have to hurry or stall later on.
• Check if music distracts any of your players particularly. Some people are more vulnerable to this.
• If you have them downloaded, rename the tracks to the mood they set for easy reference. Delete tracks you don’t like to avoid clutter.
• Consider having a signature melody for your “Previously on [campaign name]” segment. This can serve as a nice transition into the game and let people know its time to put their phone down.
• Regarding sound effects, I’d mostly forgo them in favor of creating ambiances instead. If you want to incorporate them, I’d recommend just leaving them for special occasions to avoid cheesiness. Leave it to moments of cinematic weight, like that moment where they open the huge door to the final boss, or for the military trumpet when the armies are about to finally clash. They also occupy a good amount of mental space, as you have to be ready to press the button at the exact moment.
• I’ve read some people had success with using music or effects, but still consider the effort put is not worth it. Knowing this, one could try to facilitate things by:
• Leaving music only for specific scenes or perhaps just for the battle encounters.
• Make a habit of exploring new soundtracks in your spare time, while you do other stuff, and note down which you like and their mood. This to avoid a crammed prep session the night before.
• Dedicate just one afternoon to listen to tracks and choose the ones that you will use during the whole campaign. Choose tracks that fit the theme and that cover the major types if moods and situations, like Action, Ambient, and Sinister, as Martin Ralya recommends on the Gnome Stew Blog. You can then create playlists with those and refer to them quickly later.
• If you do decide to incorporate tracks into your games, definitively look into ways a DM can delegate to other players part of the work, like tracking initiative and recording the earned gold. This will make things more manageable.
• I also just found RPG Ambiance, a very useful web application that provides a quick track management interface, that even lets you hot key tracks, arrange them in order of events, name your scenes, and play more than one simultaneously. It requires you to upload the tracks you intend to use. Play with it to see what I mean.