Disclaimer: I am not an professional sound technician or native English speaker. Some terms may have been used wrongly.

-----------------------------------------------

How to use material presented here to create ambient background soundscapes RPG sessions:

Track, ambience and singular sound
-Track refers to single sound file, either stream from YouTube or downloaded MP3 file.
-Ambience refers to combination of tracks that are part of a particular scene and are constantly running on a loop on background, while player characters remain in that scene.
-Singular sound refers to track/s that GM is able to launch quickly on top of ambience soundscape as needed.

Track frequencies
-When creating soundscape you should avoid packing too much tracks on just one frequency area, that way your ear is not able to separate between the individual sounds. Example of bad combination: thunderstorm, heavy engine and explosions (each located to low frequency area).
-Try to compile ambience tracks so that they utilize all of three general frequencies:
Low: Booms, heavy things
Medium: Human speech, medium things
High: Beeps, chirps, small things

Volume
-Ambience sound should always stay on background during a game session, so that players do not need to raise up their voices. This is tool of subliminal mood building, where sounds should mainly be heard when players are not speaking.
-Short singular sounds can be used on much higher volume than ambient ones during gameplay. Doing it simultaneously when player throws a dice gives extra immersion.
-Changing relative volume of tracks during gameplay makes sounds to come closer or go farther depending on how you change volume levels of independent tracks.

Sound speed and pitch
-With YouTube and sound editor it is possible to change speed of track and it's pitch. This gives you possibility to radically change how played track sounds.
-Slowing down or lowering pitch on some tracks ( test this on half speed) makes them sound of alien language or something weird instead of what it originally sounded of. It also makes sound source of any track to sound more larger as slower the track gets.
-With speeding up some tracks same happens as with slowing down but to other direction. Higher the frequency (increasing pitch) track has smaller the object on it sounds ( test this on double speed).

Priorities
-Are you GM or DJ? In my opinion it is more important to run a good social game than try to reach the perfect background sound. This is supplemental tool for game sessions and not an stage for cranky DJ egos.

-If several different soundscapes are needed during the game session then it is better to do some work beforehand. Create ready MP3 file/s of ambience soundtracks beforehand as transition from one scene to an another can be instant with pre-made tracks.

Lazy persons soundscape creation with YouTube

1. Open required amount of YouTube pages on your web browser.

2. Search wanted ambience and singular sounds from YouTube pages.

3. Pre-adjust each of YouTube page's sound volume to suit your soundscape.

4. Put ambience sounds on a loop and singular sounds ready and paused.

5. When soundscape is ready, set it to mute from your computer volume control and just let the soundscape loop on.

6. When players have arrived and are ready to start the game just unmute your computer and keep ambience running through whole game session.

7. Use singular sound/s during game as needed.

- Plusses : Easy to set up.
- Minuses : Requires internet connection. Prone to browser crashes. If several soundscapes are needed during session change from one to a another is slow.

In depth soundscape creation

-If you plan to use several different soundscapes during a game session this approach makes it fast and easy compared to a YouTube method.
- Download required sound tracks as MP3 from YouTube and edit them by using Mixer or Multi-track editor .
- Plusses : When work is done you do not need internet connection during the gameplay. You have better control of volume levels of tracks (and reverb, pitch, etc). Possibility to edit downloaded tracks. Larger sound libraries available as you are able to snip required parts from "sound effect bundles" available on YouTube. Fast transitions between premade soundscapes during gameplay is easy.
- Minuses : "All work and no play makes a Jack a dull boy." You need to learn to use mixer/editor. You have to download your sound library to a computer to be able to produce meticulous content. You do not have time to sleep or write the game because ending of three different tracks need to be synchroniced.

Examples of easy YouTube soundscapes

Trench Warfare :
My first idea of the soundscape to use during RPG game was set on WWI trenches.
Ambience: Constant rainfall and distant explosions .
Singular: Infantry charge is used each time the player characters start their attack.

Imperial Guard jungle operation:
This was developed for game set on a jungle planet where the players had characters of Imperial Guard heavy weapon team.
Ambience: Either Jungle day or Jungle night depending of the time of a day at the game.
Singular: Autocannon (used by player characters during their heavy weapon shooting actions) and Constant warfare (Continuously on during endgame after enemy reaches the lines Imperial Guard is holding).

--------------------------------------------------

Following ones are latest ideas that I have been designing for my current campaign:

Imperial frigate bridge :
Ambience: Millenium falcon engine , Factory sounds and Beeping machinery .
Singular: Battle ambience distant (during inevitable void combat), Small arms fire (if star vessel is boarded during void combat), Nuclear alarm (if star vessel receives critical hit during void combat).

Techshrine of Omnissiah :
Ambience: Mechanicus ambient 2 , ROBOTIC welding and Orbital transmissions .
Singular: Geiger counter used by a tech-priest to scan the characters.

Lair of the heretical cult :
Ambience: Cave with dripping water , Beeping machinery , Bubbling in a cave and Demonic whispers .
Singular: Demonic chorus when chanting starts and Daemon of Nurgle when the daemon is summoned.

Inside void suit and engaged to combat :
Ambience: Space helmet breathing , Heartbeat fast and Combat radio chatter .
Singular: Plasma gun sound when the character shoots enemies.

Daemon of Nurgle :
Ambience: Bubbling ooze , Swampy thing , Flies buzzing and M onster sounds , Quotes from "Heart of Decay" audio drama .
Singular: Godzilla breath when it launches attack with daemonic powers and Unnatural evil laugh when it is taunting the characters.

------------------------------------------------------

Ready made soundscapes by others:
Battlefield Ambience | Ambient Sound Effects for WH 40K 1 hour
Necron invasion vs Imperium 1 hour
Xeno invasion vs Imperium 1 hour
Exoplanet -Forest Ambience Sounds, Sci Fi Insect and Fantasy Creature - 5:49
Xeno planet 3:43 minutes
Victim of Nurgle's blessing in the rain 1 hour

-------------------------------------------------------

I have created library of suitable sound effect and ambience tracks from YouTube, sorted by general and vague topics. I will be expanding and organizing it further as there is time left over from actual game mastering.

Sound effect library is collected from sounds planned to be used in WH 40K campaigns and majority of the sounds can be classified to sci-fi/combat/industrial/urban/horror/etheral effects.

Edited June 26, 2019 by Olenkoen