By Jo Brodie and Paul Curzon, Queen Mary University of London
Computer-based musical instruments are so flexible and becoming more popular. They have had one disadvantage though. The sound could drag behind the musician in a way that made some digital instruments seem unplayable. Thanks to a new computer called Bela, that problem may now be a thing of the past.
If you pluck a guitar string or thwack a drum the sound you hear is instantaneous. Well, nearly. There’s a tiny delay. The sound still has to leave the instrument and travel to your ear. The vibration of the string or drum skin pushes the air back and forth, and vibrating air is all a sound is. Your ear receives the sound as soon as that vibrating air gets to you. Then your brain has to recognise it as a sound (and tell you what kind of sound it is, which direction it came from, which instrument produced it and so on!). The time it takes for sound and then your brain to do all that is measured in tens of milliseconds – thousandths of a second. It is called ‘latency‘, not because the delay makes it ‘late’ (though it does!), but from the Latin word latens which means hidden or concealed, because the time between the signal being created and being received, it is hidden from us.
Digital instruments take slightly longer than physical instruments, however, because electronic circuitry and computer processing is involved. It’s not just the sound going through air to ear but a digital signal whizzing through a circuit, or being processed by a computer, first to generate the sound which then goes through air to ear.
Your ear (actually your brain) will detect two sounds as being separate if there’s a gap of around 30 milliseconds between them. Drop that gap down to around 10 milliseconds between the sounds and you’ll hear them as a single sound. If that circuit-whizzing adds 10-20 milliseconds then you’re going to notice that the instrument is lagging behind you, making it feel unplayable. Reducing a digital instrument’s latency is therefore a very important part of improving the experience for the musician.
In 2014 Andrew McPherson and colleagues at Queen Mary University of London aimed to solve this problem. They developed Bela, a tiny computer, similar in size to a Raspberry Pi or Arduino, that can be used in a variety of digital instruments but which is special because it has an ultra-low latency of only around 2 milliseconds – super fast.
How does it do it? A computer can seem to run slowly if it is trying to do lots of things at the same time (e.g. lots of apps running or too many windows open at once). That is when the experience for the user can be a bit glitchy. Bela works by prioritising the audio signal above ALL other activities to ensure that, no matter what else the computer is doing, the gap between input (pressing a key) and output (hearing a sound) is barely noticeable. The small size of Bela also makes it completely portable and so easy to use in musical performances without needing the performer to be tethered to a large computer.
There is definitely a demand for such a computer amongst musicians. Andrew and the team wanted to make Bela available, so began fundraising through Kickstarter to create more kits. Their fundraiser reached £5,000 within four hours and within a month they’d raised £54,000, so production could begin and they launched a company, Augmented Instruments Ltd, to sell the Bela hardware kits.
Bela allows musicians to stop worrying about the sounds getting left behind. Instead, they can just get on with playing and creating amazing sounds.
Featured image credit: Andrew McPherson.