The other day I broke a laptop monitor in half and I recorded it using four very different microphones with different specifications. I recorded the sounds with a sampling rate of 192 kHz and loaded the sounds into Izotope RX5 to show the spectrogram and pitch down the sounds two octaves. This video demonstrates how different the sounds are when pitched down since some of the microphones capture audio well beyond what the human ear can hear - yet when you pitch the sound down those inaudible frequencies are brought into our range of hearing:
This year I went to the Nynäs Offshore Race which takes place only a 30 minute walk from my home in Nynäshamn. I brought my new "field recording kit" that may not be the most portable setup in the world, but it gives me the best option for recording directional spot mono audio using a Rode NTG3 shotgun microhpone and environmental ambiences and stereo effects with a pair of Sennheiser MKH 8040 micorphones. The mics are housed in wind-protecting Rode and Rycote blimps with dead kittens (those huge furry things to block most of the wind.) I record the 3 channels of audio into a Sound Devices 633 field mixer at 192 kHz 24 bit audio.
I recorded quite a few powerboats as the passed by - but getting usable game audio is quite tricky. I'll tell you why:
First of all, there is a PA system with an announcer that feels obligated to speak non-stop which is great for the audience but terrible for someone who wants to capture the boats and nothing else. I had to find a spot close enough to the boats, but far away enough from the diesel-powered speakers pushing out a distorted commentator voic.
Then there is the audience, they tend to chat and cheer a lot so I had to find a spot far enough away from most of them - luckily the powerboats are loud so the gain is not set too high which reduces the chance of spectator voices.
Another challenge is that you don't really get that close to the boats, they have to drive where it's deep and safe enough which isn't always that close to land.
The splashing water is another parameter to consider, but again, not loud enough to be too great of a problem.
The biggest problem, however, is that the boats pass by producing a sound that fades in and out and shifts in pitch due to the doppler effect. By default they will be great if you want to have the sound of a passing powerboat - but you could never apply that sound to a boat in a game since it simply doesn't loop well.
Turning the passing powerboat sound into looping game audio
I put together a video where a single powerboat passing by is turned into a short loop of game audio that could be used on a powerboat. If you need to do something similar, or if you are just curious what work goes into converting the sound, have a look:
I ended up using the audio from the Rode NTG3 shotgun mic this time since I didn't need it to be stereo and it produced the longest sustainable sound as I aimed the microphone at the boat as it passed by. It also contained the least polluted sound since the design of the shotgun mic blocks off-axis sounds fairly well.
This sound loop, among many others, will be included in the next update of the Universal Sound FX library.