For a number of years now, the Flight Simulator X and Prepar3D community has enjoyed an amazing freeware Douglas C-47 in the form of the C-47A Skytrain package built by Manfred Jahn and team. Recently, by courtesy of Aeroworx, that same model has been converted and released for use in X-Plane 11 once again as freeware! As this is one of our favourite aircraft both virtual and in real life we decided to develop a high quality engine sound package for both platforms.
We really wanted to push things to the limit and see (or rather hear) what could be achieved using different sound systems to simulate the same aircraft. Turning things into a kind of battle; the venerable FSX sound system vs. XPlane 11's FMOD sound system!
development for fsx
Back in november 2017 we started development of the sound package for FSX. The aircraft (as modelled) uses two Pratt & Whitney R-1830s, each engine is supercharged and drives a 3-bladed constant speed propeller. It is the unique blend of combustion, supercharger and propeller noise that results in a wonderful symphony when the engine is running.
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Accurately portraying the sound of a constant speed propeller engine, let alone supercharged, is a challenge when working with the FSX sound system. Simply put, the simulator does not facilitate correct behaviour only an approximation.
We first sampled our own recordings from the DDA Classic Airlines' PH-PBA. However, not far into development we realized we needed more source material to offer the same level of quality for both internal and external views. In the end we sourced additional high quality recordings of 3 (still active) C-47As:
- Air Colombia HK-3292, footage used with permission by Michael Prophet
- National Warplane Museum "Whiskey 7", CC-BY licensed footage by David Andruczyk
- Pacific Dakota Restorations "Oklahomal Gal", footage used with permission by David Kingshott
After gathering the necessary samples, work commenced on the interior part of the sound package (audible with camera/view inside the aircraft). We wanted to make sure that the low frequency noise from the propeller at higher RPMs would be well represented, something we found lacking in most freeware R-1830 sound packages available.
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Keep in mind that the ears of the cockpit crew are relatively close to and in front of the propellers! Without ear plugs in or headphones on your ability to hear won't last all that
Apart from the engine and propeller noise, there wasn't a lot left to do on the interior. The aircraft package by Manfred Jahn & Team already contains an entire suite of additional sound effects that bring the cockpit to life (e.g. switches, levers, etc.) and even features a voiced captain and first officer.
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The FSX sound system is very limited in regard to the number of sound effects you can add. A lot of developers have since moved towards the now famous XML sound gauge by Doug Dawson. Not entirely coincidentally... this same gauge is also used in the C-47A package by Manfred Jahn & Team.
Setting up the exterior part of the sound package (audible with camera/view outside the aircraft) is always a challenge as we have to figure out which sound is heard at what angle. In the end, no less than 17 samples were used per engine in order to recreate the sound profile making extensive use of sound cones to cover all possible camera angles.
Video 1 demonstrates the end result and shows the aircraft during an engine run-up from an external viewpoint. Listen closely and you should be able to distinguish the exhaust, propeller and supercharger noise.
Video 1: Exterior run-up
After about a month in development, the FSX version of the sound package was released as freeware at the end of 2017 as a Christmas present to the community (download links at the bottom of this article).
development for x-plane 11
Initially we aimed for a simple "conversion" of our FSX sound package to X-Plane 11. Little did we know that it would take a lot of time merely getting used to the new FMOD sound system and its accompanying tooling. After managing the learning curve we quickly realized the power of FMOD and that it would allow a far more realistic sounding aircraft than FSX ever would.
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Similar to the FSX sound system, FMOD is completely integrated into the simulator software. Contrary to the FSX sound system, FMOD has access to all output variables or "datarefs" which
in turn allows highly accurate control over sample playback conditions. And to top it all off... FMOD also features runtime processing (e.g. equalizing, highpass, etc.)!
Using the samples from the FSX version we started building a project in FMOD Studio. Again we did the interior engine sounds first, this time also configuring interior sound cones and processing effects such as equalization and reverbiration. These added features combined makes moving the camera from the cockpit into the passenger cabin a very dynamic experience as you navigate through the propeller noise.
Next, we added a lot of sound effects that are audible inside the aircraft. From switches to levers to windshield wipers all were assigned a sound effect. Most of these samples are re-used (with permission) from the C-47A Skytrain package for FSX. But we didn't stop there! FMOD allowed us to add some novelty sound effects as well such as realistic rain effects, stall buffeting and dynamic wind noise.
For the exterior portion of the sound package, the end results are even more dramatic as you'll discover viewing the videos shown below.
Video 2: An evening takeoff and overhead fly-by
Video 3: Runway side and cockpit takeoff
Highlighting one of the major features of the sound package; Video 2 demonstrates the sound realistically fading into the distance. Notice the supercharger whine as the aircraft approaches the camera and how quickly the sound changes when the aircraft flys overhead.
Next, Video 3 shows another takeoff recorded from different perspecives; runway side and in the cockpit. In the exterior perspective, note how the loud "propeller slap" subsides when the aircraft starts rolling and the powerful blast of propeller noise hits the camera as the aircraft moves in front of it. This is the stuff we dreamed about but could never achieve before!
The cockpit perspective shown in Video 3 the previously mentioned propeller slap is even more prominent as engine RPM increases. Recall the captain's ear is very close to the propeller blades... Again, as the aircraft starts moving, the propeller slap subsides and when engine speed is reduced to 2050RPM after takeoff we settle in a smooth and gentle humm, awesome! :)
In conclusion we hope this article has provided you with some insights into our development process. That being said... on to the next one!
Oh, and if you use either FSX, P3D or X-Plane 11 well... what are you waiting for? Give it a go! Scroll down to the bottom of this page for the download links.
sources and links
- Aeroworx DC-3 Development Log at X-Plane.org forums
- David Andruczyk's YouTube channel
- Pacific Dakota Restorations on Facebook
- Trevor Morson's DC-3 website, contains a wealth of information
- Vintage Aviation Pictures website by Michael Prophet