As yesterday’s post pointed out, the GDC Vault has slide shows and audio recordings from Forza Motorsports 3 designers Mike Caviezel and Greg Shaw at GDC 2010. I put in links in yesterday’s post, so be sure to check it out.
So, it’s time to talk about some of the info in that presentation. I first and foremost need to commend the Forza team for correctly realizing that the most important interface for car-to-driver communication is through the tires, and specifically the sound the tires make. A race car driver’s primary job is to manage the grip at the four (or less or more) tires at all times as efficiently as possible. Going back to physics class, if you remember talking about friction, then you’ll remember that there are two states of friction: static, or non-sliding, and kinetic, or sliding. Static friction is a stronger force than kinetic friction. In a rotating tire, the rubber against the road is in a state of static friction. As you push the wheel more, your applied force will exceed the tire’s static friction and go into a state of kinetic, or sliding, friction, which means doing a burnout if accelerating, over or understeering if cornering, and locking up if braking — all of which is slower than when the tires are in static friction. Thus the absolute limit of a car’s performance will be having the car always on the brink of going over to kinetic while staying in static friction.
Fortunately, the rubber of the tires will make sounds to let you know what’s going on. As the rubber of the tire is subject to forces pushing or pulling on it while rotating around, the rubber can start to vibrate in a way that sounds like a “howl” or a low-pitched hum. This is actually the tire juuuuust starting to hit kinetic friction. The more the howl or squeal gets louder, the more kinetic the friction is becoming. Therefore for a performance driver, hearing the tires is an important part of the job. So, Kudos to the Forza team for integrating this as a core part of their gameplay system. After playing forza 3 for a long while, I have to say, the tire audio feedback system is head and shoulders above any other game I’ve played. However, and Mike talks about this in the presentation, the ratio of no-sound to howl to squealing is a little bit off, with the howl being accentuated. This is a good thing for gameplay as it gives the player better communication. However, if you’re looking for a strictly simulator feel, then this isn’t quite going to get it for you.
Second, it’s worth checking out the crazy rigs the Forza team put together for getting gear, supercharger, and turbocharger sounds. Capturing those sounds that are unique to modified cars is something that I’m glad the Forza team decided to dedicate resources to, because car enthusiasts who know what those sounds mean go crazy when they hear them. Just walking to the store and hearing a blow off valve in the distance gives me rubberneck syndrome. It’s those sounds that scream “I’m special” and “I’m fast.” Their integration in the game is great but I want more! Especially the superchargers.
Also, Mike included a very important formula on the slides:
RPM = (Fundamental Frequency * 60) / Number of Cylinders.
This is important because, in a video game setting that uses loops of steady-RPM recordings with pitch shifting to go between them, the dynomometer number has some inaccuracies to it. (According to Mike, up to 100RPM error!) Thus, being able to back-calculate what RPM your recording is at means being able to correctly stitch the loops together. This also means, if you reverse the math a bit, that when you know the number of cylinders and you know the RPM range, you also know how high you can set your high-pass filters to for cleaner recordings.
I could talk for days about how awesome it is that Mike and Greg shared this information with us, but it’s time to put my little one to bed. So, as a way to say thank you, please go to the GDC Vault and read the presentation and maybe even purchase the audio recording of the presentation.