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As much as I love the written word, I can't explain this properly in text only, so please take a listen (and look) at the video that accompanies this article. But for text-lovers everywhere, there's a transcript below.
Here I am in the lovely, warm acoustic environment of my living room. Well, it's nice and warm but the acoustics could use some work. I chose this space to record in because often in film and TV drama it is useful to be able to hear an acoustic environment that matches the space that you see in the images. Whether this is recorded for real or simulated in post-production, hopefully you won't be able to tell. But in this instance the acoustic is definitely real, including some traffic noise in the background.
The microphone that I'm using is sometimes known as a bit of a 'magic mic'. I'd say that it's good at its job, which is mainly for recording dialogue. It's the Sennheiser MKH 416 short shotgun mic, and I have it positioned at the level of my forehead, pointing down at my mouth at a distance of about 20 cm.
So my voice should sound great, and my Northern accent clearly and cleanly recorded. And you should hear some of the ambience and background noise too.
But listen carefully. Listen on headphones to get a crystal-clear audio experience. Notice that everything is exactly dead-centre in the stereo image. My voice, the ambience, the background noise. It's all mono. It sounds good, but it doesn't sound like it would in real life. For that, we need stereo...
I've changed mic. Now I'm using a Beyerdynamic MCE 72 PV. It's a stereo mic that uses the coincident crossed pair principle. I've positioned it as closely as I can in the same way as the 416.
You will hear my voice in the centre of the stereo image as before. But now you can hear the ambience and background noise in wonderful stereo. It's much more realistic and much more like actually being here in the room.
So stereo is better then?
Er... It is up to a point. But the problem is in the steadiness of the centre image, which is my voice. If I sway just a couple of centimetres to one side or the other, my voice moves in the stereo image. I can make it more obvious, but even small changes in positioning are extremely distracting for the listener.
The moral therefore (and yes, I'm back on the 416) is that dialogue should be recorded in mono, which can be panned anywhere in the stereo sound stage in post production. This applies to vocals in music too as a wandering stereo image would be hard to listen to comfortably.
But what about the stereo ambience and background noise? Listen closely. Can you hear it now, with my voice dead centre?
This time I've used the 416 as the main mic, and positioned the MCE 72 PV pointing away from my mouth so that it picks up the ambience in stereo. I've mixed in the ambience to what I consider to be a realistic level.
So the moral of my story is that the human voice is is usually best recorded in mono, with stereo ambience mixed in when you want it.
One more thing... If you look up this topic on the web, you will find that it is often said that stereo causes phase issues. Well with a coincident crossed pair stereo mic setup, that won't happen. But the wandering centre image will always be a problem.