Audio Delay Calculator

Sound moves through air much more slowly than light. While light travels at around 299,337 km (186,000 miles) per second, sound covers only about 342 metres (1,120 feet) per second. This relatively slow speed is what makes echoes possible. When a sound reflects off a surface such as a wall or a mountain, the delay you hear depends on the distance. Close to the surface the echo is short, but as the distance increases the echo time lengthens. To work out the true echo time, remember that sound has to travel to the surface and back again, so the distance is effectively doubled.

Public address systems give a good real-world example of this effect. In places like railway stations, speakers are often placed in a line along a platform. A listener first hears the sound from the nearest speaker, then slightly later from the ones further away. When several arrivals overlap, announcements can become hard to understand. For safety-critical messages, performance standards such as RASTI are used to measure and ensure speech intelligibility.

To overcome these problems, engineers use signal delay units. Modern versions are digital processors that hold back the audio feed to more distant speakers by a few milliseconds so everything stays in sync. Some units can be configured simply by entering the distance between the speakers, which is then converted to the required delay time. More advanced DSP systems can also apply functions such as compression, equalisation, filtering, and routing, alongside time alignment.