Although you may not have thought this was possible with an Arduino alone, an Arduino Mega can in fact record analogue audio to a memory card in real time. This process has been researched and demonstated by Richard Patterson who enables a Mega to capture 8-bit mono audio with a sampling rate of 9.4kHz.
Some external circuitry is required to attenuate the incoming signal, and the Arduino sketch is an interesting learning exercise in timer interrups and analogue-to-digital conversion. Furthermore the audio can be saved in numeric values to be analysed with other software if required.
Overall this is an interesting exercise and well worth studying if you're interested in pushing the limits of your Arduino - so visit Richard's Instructable to get started. And for more, we're on facebook, Google+, and twitter - so follow us for news and product updates as well.
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Quite simply the EtherMega is the fully-loaded Arduino-compatible board on the market today. Apart from being completely Arduino Mega2560-compatible, it includes full Ethernet interface, a microSD card socket, full USB interface, optional Power-over-Ethernet support and still has a circuit prototyping area with extra I2C interface pins. So if your project is breaking the limits, upgrade to the EtherMega today.