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CIRRUS LOGIC AUDIO CARD FOR RASPBERRY PI COMPUTER
Cirrus Logic recently introduced a new audio board for the Raspberry Pi educational computer.
Price just £25! You can listen and record hi-res digital, so Noel Keywood did...
The Cirrus Logic audio card for the Raspberry Pi computer is, quite simply, monstrously complex in underlying structure and beyond easy description. I will keep this review short and sweet and non-technical, so you get the hang of what it can do from a high-fidelity perspective – and whether it may suit you or your son/daughter, bearing in mind Raspberry Pi is an educational computer that has sold 4 million units around the world to date – and is probably better known to those under 20 years old than those over it.
The Cirrus Logic audio card we reviewed (Version A1.01) is relatively new, taking over from a Wolfson predecessor and sent to us by element14 of the UK, who produce it, so it’s recent and representative. My 15-year-old son Douglas was given the task of getting this new Raspberry Pi 2 Model B up and running since he is part of its target educational audience, knew about it and has a view. You can read his experiences and views separately HERE.
This tiny audio card, price £25, will play digital music files stored in Raspberry Pi’s microSD card memory, using a music player bundled with the Cirrus Logic audio card drivers named LXmusic. Both analogue and digital outputs are available to drive headphones or hi-fi. We are talking about being able to play top quality, high-resolution digital audio files here (24/192): the board is a full blown hi-fi product, not just a geeky MP3 player.
But that is far from all – this little board will also record analogue audio to a digital file directly, since it possesses internal analogue-to-digital convertors (ADCs) as well – and that means it can record LP, radio or anything else – even speech. It can record digital direct too, through a normal (phono socket) electrical S/PDIF input.
And there’s even more. Two on-board miniature (MEMS) microphones enable it to record stereo sound direct, and a tiny on-board Class D 1.4 Watt per channel power amplifier can drive loudspeakers. Awesome at the price!
The card has three major silicon chips on-board, the key item being a Wolfson WM5102 audio Codec (coder/decoder). It is a fiercely complicated chip designed for mobile phones, tablets, what have you. The remaining two chips are a WM8804 S/PDIF transmitter and receiver, showing that digital audio connectivity has been taken seriously, and a WM7220 digital microphone module.
The WM5102 audio codec possesses no fewer than six ADCs and seven DACs on-board, all with a respectable hi-fi specification, even though this is a mobile ‘phone chip. The 24bit resolution DACs have a quoted 113dB range – better than CD’s 102dB – and they met this under test. The 24bit ADCs have 96dB range.
There is a Digital Signal Processor (DSP) to handle audio manipulation, and standard sample rates quoted are 4kHz up to 192kHz.
The two Class D loudspeaker power amplifiers need their own 5V, 2A power supply – if they are used. This explains the audio board’s d.c. input socket. You must also solder in loudspeaker connecting pins, so some DIY is involved – plus the ability to use a small 15W soldering iron, steady hands etc!