I met up with Gareth Jones at the Bioacoustics department at Bristol University – to show him what I’ve been doing, and to get his feedback on how I can develop the functionality of the device, inspired by how Bats use sound to navigate.
I started off by demonstrating how a sonar distance sensor could effect the ‘echo repeat rate’ of my voice – just using my laptop, arduino and the sensor. I explained how we plan to develop it into a mobile, battery powered box, and that it would be used by a choir of approximately 10 singers. I also showed him a mock-up video that just visualizes (from above) how the choir could move around having their voices effected by proximity to each other. (Each arrow represents a singer – with their sonar sensor facing in the direction of the arrow). Have a look here.

It was good to be able to show Gareth a more practical demonstration of my idea, and we went on to discuss what aspects of Bat’s sonic behaviour could be modeled in this manner.  We had a really interesting chat – and, again, I learn a huge amount, as Gareth is very clear in his explanations and descriptions.

To summarise – these are the sound transformation and bat behaviours we thought could ‘read’ most effectively.
1 – Echo repeat rate  - As you get closer to someone, your voice echoes at increasingly faster repeat rates.
This is an analogy to how bats increase the rate of their echo location pulses wen they get close to an insect. This is so they can get a more accurate ‘update’ on where the insect is and be able to accurately locate it. When listening to bats on a bat detector, you can hear the pulses get closer and closer together, until the pulses almost join up into what is known as a ‘terminal buzz’.

2 – More Notes added – as you get closer to someone, the echo repeats start to modulate to different notes to the one you are singing – changing note more frequently the closer you get to someone. 

This is an analogy to when Bats use  ‘Jamming Avoidance’. When Bats fly close together, they adjust the pitch of their pulses so as not to get confused with each other’s echoes. This is a strategy for insuring they don’t’ crash into each other when flying in groups.  (in addition to the ‘strangeness filter).

3 – Harmonising  – as you get closer to someone, another note (from the harmonic series) is added at the same time as the one you are singing. 

This is an analogy to when Bats fly in busy areas – such as woods and foliage. They add in more harmonics and overtones to their call, so there will be a wider range of returning echoes to give a more detailed ‘image’ of the surrounds.

4 – Note bending – your sung note gets modulated slight higher – the closer you get to someone.

This is also needs to happen in conjunction with slowing down when getting close to someone – and is an analogy to how horseshoe bats use Doppler shift. Their ears are tuned to be most receptive to a specific frequency, so they adjust the pitch of their ‘call’ based on how fast they are flying so the echoes will be closest to the pitch they are tuned to hear most clearly.  As they approach prey, they will tend to slow down, and therefore slightly raise the pitch of they call.

A really interesting meeting, which highlighted a lot of ideas to work with, ....  maybe not all these transformations will be in the piece, but it is certainly a rich starting point for creative exploration with the choir.