You can do that with Audacity, too. If the sound sources are of different sample rate, the first thing is to convert them to be equal and the second is to change their speed back to original. I mean, if you have a sound clip of 44100 Hz and you want to produce a 16000 Hz sound, you can convert your source, but its speed will drop and its length will raise. So you'll have to multiply the speed by 2.75625 to get the original pitch and length (44100/16000=2.75625). The effect "change tempo" will retain the original pitch, whilst "change speed" doesn't. Their values are given as percentage, so adding 100% equivalents of multiplying by 2 and similarly adding -100% means dividing by 2. Very basic maths, as you can see, but it may take a while to get used to. Listen to my
Brewster starting sound: The original inertia starter video was several minutes long, as was the Trojan video. I stopwatched the ingame time for the Brewster start with exhaust puffs and such and worked accordingly with the mix. I added silence to the actual engine sound and tried to find a significant part of the inertia starter into the beginning, fading it in. Remember, the sound wave in the end of the start clip had also to be matched to the one of the actual engine sound, meaning that it had to end in a zero point and coming from below because the engine sound starts by raising from zero.
Another important thing concerning AH sounds is the file size. Having long sound clips with lots of kilobytes and a high sample rate is asking for trouble. Look at the sample rates and lengths in other sound packs and work accordingly.