Arduino will only handle very low sample rates compared to the standard 44.1khz which you would require minimum for audio (for musical purposes). It's due to the clock speed and the inbuilt analogue-to-digital converter. Here... read this article: -
In particular, the section entitled 'Successive Approximation'. It explains how the ADC in an Arduino actually works and then goes on to show how, due to 'Niquist Theorem' the highest possible sample rate you can achieve with an Arduino UNO R3 is 4.8khz which in comparison to CD-quality (44.1khz) is pretty bad.