Friday, 30 March 2012

Got your ears on?

I just updated my audio editing/mixing software. As part of my ongoing tidying and rationalisation I found a fair number of old audio tapes and so I've been slowly digitising them ... and this got me thinking about podcasts. The range of material available, basically as an MP3 audio file which you listen to on your computer or mobile device, is staggering. Even we got in on the act since there are a few project management interviews available on our web site.

I'm not a big consumer of podcasts, I must admit; but when I listen I listen on headphones. One thing they tell you when you work in audio is that you should never do critical work on headphones, so things do sound different that way: different from speakers that is. One thing you'll notice is that everything seems to be inside your head. Now this might not bother you, but for some people it's a big source of fatigue, and one reason why you're unlikely to be completely comfortable listening on headphones for several hours at a stretch.

This can be alleviated by adding some 'space' into the sound. Stereo helps (our podcasts have some stereo music although the voice is mono) but still doesn't replicate what we would hear if we were actually there. For that, the enthusiasts say, you need true binaural recording. In this, microphones are placed at the end of (real or synthetic) ear canals ... just where the headphones would go. This is known as dummy head recording and it is possible to buy special dummy heads for this purpose ... at a price. The reasoning behind this is all down to how we determine where a sound is, which is the result of a combination of relative volume and time delay (phase) between our two ears. The physical structure of our ears affects this as sound bounces around our outer ear's shape as it makes its way into the ear canal and hence to the rest of our auditory apparatus.

To be honest, you can improve the headphone-listening experience a lot without going to the extremes of a dummy head. You can record the voice with a stereo pair of microphones so that the sound of the voice is heard with ambient sounds and reverberation around it. (If you do this then you should still record close to the person speaking since it's very easy to get too much ambience around the voice.) For two people chatting you could position them a few feet apart (sitting next to each other on a sofa is good) and have each hold a mic. It's extraordinary how realistic what I'd call the sound field sounds on headphones when the mics are a little way apart.

Which leaves you asking why the voices on our podcasts are mono. Good question. In this case it is because the recorder I used was a little more hissy than I would have liked, and making the sound mono reduced the hiss. The background hiss wouldn't have been a problem when listening on speakers, but on headphones it was more obtrusive.

There's more in the chapter on audio asset production in the third edition of our book. This is a few years old now, but the basics still apply.