I'll double the suggestions of products like the Scarlett series mentioned above, though I would suggest getting at least the 2i2 as it allows for more flexibility than the Solo. On the 2i2 you can put 2 microphones in front of your guitar or amp, you can record a direct signal and a microphone signal simultaneously, and of course you can record 2 guitars at once.

Personally, I prefer at least a 4 channel interface, just for the creative possibilities. Acoustic guitar with live vocals - 2 mics on guitar, one on vocals, and guitar on a DI blended with mics, for example, just to record one person.

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