A BBC EARTH BLOG: NATURE COMES ALIVE! How binaural 3-D audio is transforming our listening experience
With the rise of digital media we are listening to an increasing array of audio content that includes music, digital radio, audio books and podcasts. Listening to these audio sources by cranking up the volume on our personal headphones is a way to escape the stresses and tensions of our noisy urban lives by shutting out the world around us, and tuning in to something else. As part of this personal audio revolution many of us are turning to nature for solace and relaxation, and demand for field recordings of our natural environment to listen to at home, at work, or ‘on the go’ has increased. At the other end of the spectrum, the rise of virtual reality hardware, has created simulated environments to explore, designed to immerse us in alternative worlds distinct and apart from our own. Both require a ‘surround sound’ audio experience, which has led to a resurgence of interest in 3-d binaural audio, technology that has been around for over a century but has had a renaissance due to its ability to reproduce an immersive audio experience.
So what exactly is binaural 3-d audio? Professional nature recordist Lang Elliot explains binaural as “hearing with two ears, as we humans do”, and goes on to define binaural recording as “using a microphone setup that simulates the human listening apparatus”. The sound is ‘captured’ exactly as we hear it, with every element of our 3 dimensional hearing experience recorded by two special microphones, set apart from each other like ears, which emulate the functions of the human head, and can pinpoint and record the sounds we hear in the exact location that we perceive them. As our ears are located on either side of a dense skull, with a sponge-like brain in between, each ear hears the same sound at a different time. Depending on how loud and in which direction the sound emanates from, the brain is able to process and assimilate these tiny fractions of strength and time to map out an accurate signal location. Similarly, the microphones used in binaural recording are designed specifically to replicate these functions, and to be more effective, can be placed within a soft head shaped mould complete with ear canals. By being so close in structure to the human head, all the complex audio frequency variations that occur (which are known as head-related transfer functions – or HRTFs), are recorded to create the 3 dimensional effect of ‘normal’ hearing when we listen back on 2 stereo speakers, or headphones. Of course we are not actually listening to the sounds recorded from the multiple locations and directions that we would be hearing in real life, so the 3-d audio processing used in the binaural recording is in effect, tricking our brains into believing we are actually experiencing this multi-dimensional soundscape, whilst listening back only using binary stereo speakers.
When it comes to listening to the sounds of nature this method is extremely rewarding, and very effective. The sound of a bird swooping overhead, crickets chirping in unison from multiple directions, insects buzzing, and the gentle audio ambience of the natural environment with it’s multiple sound sources can be recreated perfectly using this technique. Tuning in to field recordings made with 3-d binaural audio, it is possible to completely immerse oneself in the sounds of nature and reap the benefit of these often soothing sounds which have been proven to alleviate stress and improve general wellbeing.
There are some challenges however. Binaural audio recording is usually enacted using soft head microphones to replicate the ears and head, but each person’s ears and head are different, and this can affect the timing and distance of the sounds we hear. If the person listening back has a different head shape to the original soft head microphone set up, then the recording won’t seem as effective to them.
Doing accurate field recordings also presents difficulties beyond just the microphone technology, as German field recordist Sebastien-Thies Hinrichson says – “When you do nature sound recording with binaural microphones you have to find locations that are free of human-made noise.”-
Microphones are extremely sensitive and can record sounds from miles away, such as traffic and high altitude aircraft noise. But there are some useful tips for minimising these unwanted noises, which when adhered to, can improve the recordings immensely, such as recording nature at dawn – the dawn chorus is not only loud, but occurs at a time in the early hours when human activity is at a minimum. Also following nature’s pointers can help – a warm, still summer’s morning will yield better results than a windy, rainy one where the ambient and delicate sounds of wildlife will be obscured by the noise of the weather (unless the sound of heavy rain is what you are aiming to record!). And of course, being as far away from human activity as is possible. After all, the aim of binaural 3-d audio, especially when recording the intricate and unspoiled sounds of nature, is to improve a listener’s experience, and by doing so, create an audio world that is wholly satisfying and completely immersive.
Written by Chris Knowles