Adding audio for AI helos

Sound is an impressive tool. And something I worried a great deal about from the start. Just adding various audio sources to the Apache, from the Betty, to various computers tones, compressor noise, all adds to a sense of cockpit space.

The Chinook needs similar attention, as a non-hero aircraft (currently a non-flyable). The game engine uses OpenAL, which employs a system of 3D positional audio. In the Apache most of the noise is behind your head, looking left and right appears to pan the audio. Externally the engine and compressor sound sources are attached to a helicopters engine positions.

The difference between the hero-ships such as the Apache and AI units is the way audio is initialised. Apache audio is split between interior and exterior sounds; interior sounds are built during the player boarding process which initialises the cockpit and switch status, the exterior audio is created as soon as it enters the 3D world.

Our CH-47 Chinook like the Apache, will have engine sound sources attached upon the object creation process, and the LUA update function, called every frame will swap in and adjust the volume and pitch of various audio files.

Getting really good audio requires at a number of digital recorders positioned around the aircraft. As we don't have local access to a Chinook and a bank of digital recording equipment, the modern internet age comes to the rescue with numerous video web sites rich with source material of variable quality.

After auditioning a few choice videos, using a Firefox web-browser plugin that downloads the video files from these sites, the process of ripping the audio for processing can begin.

VLC Media Player is a free video player with a number of conversion features. And allows you to batch export audio from a video files using the Convert option.

Selecting the video we want to convert and the destination file then choosing the export format. We want audio only and in OGG format.




I have the Audacity

Don't leave home without it. Audacity is in my price range (free) and works well with OGG format audio files.

It's reasonably easy to find and build audio loops but before you can do that you need to turn it onto a mono audio file. OpenAL's 3D positional audio requires a mono-sound source, it will split the sound to different channels depending on the source and listener position. So having flattened the audio file, the work of finding and snipping loops can begin.

In the next blog update I'll detail the processing of adding and loading the sound files in the model's LUA script.