Billed as ‘the ultimate Raspberry Pi 3 microphone’, the Andrea PureAudio Array Microphone Development Kit (MDK) is a three-part product. The first is an Andrea SuperBeam stereo microphone. The second is a PureAudio USB sound card with 3.5 mm microphone and speaker jacks, without which the software – the third part of the bundle – won’t run.

This article first appeared in The MagPi 69 and was written by Gareth Halfacree

The USB sound card is used as a hardware token to prevent unauthorised redistribution of the software. It does not, however, provide special processing functionality.

The absence of hardware implementation has an impact on performance: while recording or listening for its activation phrase, the sample application caused a 60 percent increase in power draw and a sustained 30–40 percent single-core CPU load – a big impact for anyone working on an embedded design.

Audio filtering

The primary feature of the MDK is an audio filter library which uses Andrea’s various technologies to improve the performance of the microphone in various conditions. Active noise cancellation drops background noise considerably, a beamforming mode helps when the speaker is off-centre from the microphone, and echo cancellation works to prevent speaker audio intruding on the recording. All these work well.

However, software must be specifically built to use the library. The only software that makes use of it at present is the extremely limited PureAudioPi sample application included in the bundle as source code, which listens for the preset key-phrase “Hello Blue Genie”, then triggers a ten-second recording.

The functionality of the kit can be extended, at a cost: add-on ‘vocabulary packs’ are available for £9/$10 each. These add the ability to recognise simple commands such as ‘up’, ‘down’, or ‘today’s weather’, but they come with no built-in functionality beyond printing confirmation to the Terminal, and you can’t build your own vocabulary packs either.

Last word

2/5

While the filter library is smart, being tied to a specific USB sound card and requiring significant resources make the MDK hard to recommend.