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Recording Cars

April 27, 2009

Tim Prebble’s recent Music of Sound posts, about recording the sound of an old V8 motor, have got me thinking tactics for a car recording of my own which I’ve got coming up in a few weeks time.  As I mentioned in my last post, I’m interested in experimenting with dynamic mics and, specifically, kick drum mics to try and capture extra ‘punch’ and low-end in certain types of sounds I record.  I think cars are definitely one such type of sound.  This is partly due to the results from my last car recording session.

This previous recording took place a couple of years ago for a film called “Doomsday”.  I only had a morning to record four different muscle cars, so I used the  same setup on each car as, unfortunately, there was no time to do tests, tweaks and sound checks.  Part of this setup included using DPA mini omnis on the exhaust and engine.  As an experiment, I also placed a Schoeps boundary mic inside the car, taped down to the carpet in the footwell.  This meant it was quite close to the exhaust which was generally at the side of the car.

The results were great.  The DPAs are obviously great for tucking in any nook and cranny but most importantly their low sensitivity is great for isolating the high velocity engine or exhaust sound from the lower level wind and road noise, and the subsequent recordings had excellent clarity in the mid frequencies.  The only slight disappointment was that the DPAs maybe didn’t quite capture the low end grunt of these cars’ exhausts as well as I’d hoped.  Interestingly, the boundary mic picked up these lower frequencies the best of all the mics I used, and I’d be tempted to try using one again.

The problem here is the inability to listen for a ‘sweet spot’ on the exhaust or to truly test whether the DPA is giving an accurate record of the sound that is emitted that close to the exhaust.  As Tim mentions in his post, when setting up a mic on the engine, you can stick your head under the bonnet and listen for what aspect of the sound you want to focus on (or avoid).  However, if you value your eardrums, that simply isn’t possible with the exhaust.  

Therefore, my only experience of the exhaust sound is either from a considerable distance or as a massively gain-reduced version, monitored through headphones.  

With regards to distance, listening from even a few feet further away does sometimes seem to allow the full character of the exhaust sound to manifest itself better.  I know that lower frequency sound waves travel further than higher frequency ones, so maybe this explains why the DPA recording taken from the mouth of the exhaust seems to contain more mid and high frequency content than the sound I hear with my own ears ten or fifteen feet further away.  In that case, maybe the technique of putting the mic on the end of a fishing pole boom which is somehow attached to the back of the car could be the answer.  This is definitely something I’m going to look into for my upcoming recording session.  

With regards to monitoring through headphones, this won’t really give you an accurate representation of what you’re recording anyway, as the sound from your headphones will inevitably be coloured by the sound coming directly from the car.  This effect is described here in an interesting commentary by Al Fasoldt.

I think the best bet could be to try and set up combinations of DPA omnis and kick drum mics close to the exhaust and on the boom pole, otherwise there’s no way of doing accurate A/B comparisons and, therefore, no way of knowing whether a kick drum mic handles the exhaust sound any better than a DPA mic does.   At this rate, even with two recorders I’m going to be struggling for inputs!

From → Post Production

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