As you can see from my mind-map above, sound in games is split into two categories; Diegetic and non diegetic.
Diegetic sounds are sounds that can be heard from things that you can see in the game. A common diegetic sound is ambient noise when being in environments, obviously this depends on what environment you are in. A good example would be when walking through a forest hearing a flock of birds taking off out of the trees as you walk by or when heading through a city hearing the traffic and chatter of cars and people around. However, diegetic sound does not need to be ambient noise, it can be any sound that comes from something or someone that you or the player can see within the game. A good example of this is when i used to play GTA V and was doing a bank heist AI characters first reaction to me entering the area was to scream. That scream was the diegetic sound.
Non Diegetic sounds are sounds that cannot be heard by the player but can be heard by the person playing the game. The source of the sound is not from the players environment. They are usually used for a type of effect on the person playing the game or just as a background sound. Sound effects for added effect would be another good example as well as a narrators commentary. To put it simple non diegetic sound is sound outside the game-space.

In this mind-map i have expanded on the definitions and looked at good examples of both. Giving me a better understanding of what they both mean and how they are added to games and how they effect the play of the game and how it effects the person playing it.
Furthermore for research into sounds in game play. I had a look at a few videos in Minecraft, this is because Minecraft is a great game that represents a huge range of in-game sounds.
This youtuber was able to make a two and a half minute video on all the different sound effects that are made from the player or AI’s within the game. Mojang wanted Minecraft to have realistic sound effects within the game. Good examples of this are heard within the video, when the player walks over different environments the sound of his footsteps change depending on what the player is walking on. At the beginning of the video the player walks over different types of ground including; grass, snow, wooden planks etc. Showing how Mojang have wanted players to feel like they are in their own version of the real world so that people can become more immersive in the game, creating their own stories and worlds.
Minecraft can also be linked to the theme of nautical because of the recent updates that have been added to the game throughout this year making the game more interactive in the sea and giving players more things to do when they are by or in the sea.
As you can see from the video that the background music is different to when you are out of the water. When in the water all sounds created are muffled and are a bit harder to hear than it would normally when out of the water. Mojang have done this so that players get a feeling of being submerged under water in another way other than from seeing their character under the water.
Minecraft is a survival based game with there being things to collect and build and enemies to kill and run from. Because of this game comes under the genre of survival games. However, there are other games under other genres that are Nautical theme.
Depth is a multiplayer game where there are two teams, the divers and the sharks. The divers need to swim down and into ruins to find the treasure, however the other team, who are the sharks, have to stop them by eating them and tearing the divers apart. Below is the trailer for the game, cleaning up any questions about the basic idea of the game what you need to do.
This game-play of Depth is not the best to show off the qualities and effects that the game has to creating the submerged feel that it does, however it was the best one i could find. So please skip to 6:30 and watch the player leave the cage, after the scream from the player you here the background noise as he enters the ruins and actual shuts the hell up (sorta) for the first time. The background noise is made up three noises. Firstly, there is a clear ambient noise that begins the feeling of being submerged underwater, like all sounds created whilst playing are muffled due to being underwater. Then there is the piano playing with the ambient noise. This piano playing builds on the effect of the murky water and the ruins, creating an overall feeling of tension and worry for a shark to attack you at any moment.