Game Audio Tutorial - Book - Chapter 2 - Part 3

Exercise Set 2 Continued:

206b_00 Concatenation of multiple sample rates
The Concatenator node was used to reassemble sounds that were chopped into sections. To save memory whole sound files were chopped into sections with each section having different sample rate applied depending on the frequency content. In this case, gunshot and explosion sounds were used. As the initial blast of each sound had a lot of high frequency content these were sampled at the highest rate to preserve the quality. The tail end of each sound could be chopped into sections of decreasing sample rates as the frequency content faded to a low rumble. The Concatenator node was then used to play the split files back as one sound. Here is the memory savings made which on the grander scale of a full game would soon add up.
Explosion sound file before: 61.28Kb
Explosion sound file after: 46.93Kb
Gunshot sound file before: 38.85Kb
Gunshot sound file after: 22.21Kb

207_00 Envelopes
The Kismet was used here to manipulate the ambient sound emitting from an engine room of a spacecraft. 3 separate engine sound files were looping and had to have an envelope applied to them to give the sense of life by adding movement and variation. The play sound node was used to play back each sound and the fade in and out, 'variables' were exposed and controlled by a 'random float' which randomly generates fade in and out times using a minimum and maximum value to determine the threshold of in and out times.

208a_00 Kismet [Trigger Volume] take damage and [Oscillator]
In this exercise 3 sound cues referencing the same 1 second triangle wav had to be created in order to make them sound like different pulsating alarm sounds. These cues were then triggered when a generator was shot. 3 generators had to be shot 10 times each to unlock a door in the level and each generator needed its own alarm sound. The 'oscillator' node was introduced which was used to oscillate the pitch of the triangle sound to get the rising and falling sound of the pitch that would be expected from an alarm.

209_00 Muffin Trucker
The goal of this exercise was to take the pre set sounds for a small game and edit them to bring the memory usage down from 22.6 Mb to 500Kb so the game could be used for the mobile market. This task involved using all the techniques learned from the tutorial so far.

All sounds assets were edited which included removing any unnecessary material (cutting any long fade outs/ins) exporting at lower sample rates depending of frequency content and prominence of sound in the level. In doing so the assets were reduced in size from 22.6MB to 2.94 Mb but after importing the assets back into UDK, the on-board file compression tool was used to reduce the package further. This was in the form of OGG compression which then took the package size down to 369.59Kb with little noticeable quality, especially if played on a mobile device. The following video is a before and after ccomparison of this exercise.