Johannesburg, 12 Mar 2020
Here’s a scenario that may be familiar to some of you. The bus to the airport hasn’t arrived, and you start anxiously checking the time. Frustration is starting to build, when you hear the bus station’s public address system make an announcement: “Can passengers waiting for the bus to...[inaudible muffle]...please go immediately to...[indecipherable speech]...as your bus will be leaving shortly.”
In this situation, poor audio quality causes aggravation, inconvenience, and may persuade you to take a taxi to the airport in future. However, the situation could be far worse.
Imagine living in a coastal area at risk of flooding. There is an early warning system in place, so that if water levels rise significantly, an emergency alert is sent out to affected areas. Audio alerts are played through loudspeakers to give emergency instructions to people in danger. In this scenario, hard-to-understand audio doesn’t simply cause inconvenience – it can put lives at risk. For those living with the threat of floods, earthquakes or bush fires, high-quality audio is not a luxury; it can be a matter of life and death.
Digital Signal Processing
Digital Signal Processing (DSP) ensures that all Axis network speakers deliver optimal sound quality.
At Axis, we understand the responsibilities that come with supplying network audio systems. That’s one of the reasons why all Axis network speakers come equipped with DSP capabilities. DSP for public announcement is about analysing and manipulating sound to improve speech intelligibility. In Axis network speakers, several sound optimisation techniques – such as frequency optimisation, loudness compensation and dynamic range control – are built into the speakers themselves to deliver excellent audio quality in any environment.
Danny Smith, a Senior Software Developer at Axis responsible for sound and audio quality, explains that there are many advantages to having everything on the edge rather than the old-fashioned approach.
“Traditionally, you might see a control room somewhere, containing a mixing console, equalisers, compressors, amplifiers and so on. With Axis, these tasks are done through edge processing in the speakers themselves, so you get the advantage of high-quality audio without the need for a control room. It’s reliable too, because the signal doesn’t have to go through multiple pieces of equipment before it gets to the speaker, as it would in an old-fashioned set-up.
“Plus, everything is 100% digital, from source to speaker, so the signal doesn’t degrade. You don’t get distortion from electronic interference, and the sound signal remains strong, no matter how long the cables are. The signal doesn’t weaken over distance, so speakers can be placed exactly where you want them.”
Axis speaker technology – on the edge
The edge processing in Axis network speakers means they are frequency optimised, which gives the same characteristics to every speaker. As a result, they can combine without the need for manual tuning or configuration, and the system can be easily expanded just by connecting more Axis speakers.
Users can also remotely schedule speaker tests to make sure that they are functioning correctly. Every Axis network speaker has a built-in microphone which monitors its output. If the sound coming from the speaker is inadequate, the microphone picks this up and an alert is sent to the administrator. As Smith states: “If speakers are used in remote environments to warn of emergencies or to deter crime, then it’s crucial that you know they are working properly.”
Smith is happy to go into more detail about some of the automatic functions embedded into all Axis speakers.
“Dynamic range control is an important function. An audio signal will often have peaks and troughs in volume, and this feature can balance these to make sure that sound is broadcast at the ideal volume for listeners.
“Loudness compensation is another clever feature. If you have a ‘loudness’ button on your stereo, then you may be familiar with the basic concept. At low volumes, certain frequencies are less perceptible to the human ear. Loudness compensation boosts those frequencies so that the listener doesn’t miss anything. This happens automatically in Axis speakers, so they are great for background music in stores.
“It’s the application of edge processing in our speakers that makes all this possible,” Danny concludes. “For users, it means that there is no need to go on site to control audio quality, there is no risk of equipment interfering with the audio signal, and there’s no reliance on individuals programming speakers according to what they subjectively think sounds good. Axis takes responsibility for all these things. For listeners, it simply means that announcements are easier to understand!”
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