I see this question asked fairly often around here, so I put together a couple samples to try and demonstrate. The files: https://www.dropbox.com/sh/qim2nl2zeobcix8/AADx9sS6XYgDTEJRfHJfrspRa?dl=0 The two interfaces are: iK Multimedia iRig HD. Cost £80 new. A small, USB-powered, single input dongle. Their website says: "iRig HD features superior digital audio quality, and offers a premium 24-bit/96kHz A/D converter for a crystal clear digital signal that’s free from noise and crosstalk". They make a big fuss of this being a Hi-Z input specifically for guitar. I used this thing for years, jamming through free plugins and it always sounded fine to me. http://www.ikmultimedia.com/products/irighd/ Apogee DUET. Cost £500 new. Two inputs, monitor and headphone out. It's a reasonably high end interface, probably at the http://www.apogeedigital.com/products/duet "Duet features legendary Apogee AD/DA conversion, 2 world-class microphone preamps, USB MIDI I/O and ESS Sabre32 DAC technology". The comparison Gain on each interface was turned to the lowest setting. The iRig still clipped a tiny bit. Guitar is an ESP Horizon with SD 59/custom pickup. I used the lowest possible buffer setting in Logic that didn't result in hangs. Guitar, cables, pick etc etc were all the same. The files: 1. Processed double tracked guitars. 2. Raw DI tracks (double track mixed down to one stereo file). 3. Background noise with guitar volume at 0 My observations: Higher buffer settings meant latency was worse with the iRig. You can hear my double tracking is much worse. Latency was around 40ms with the iRig and 10ms with the DUET. The DUET has WAY less background noise. Set to the lowest input gain, the iRig is still louder and clipped a couple times. I compared the EQ of the two DI files, and the iRig has 6 to 9dB more signal at 15-20khz. I can only presume that is noise, since I don't think guitar DI would really have frequencies that high. The DUET also has a bit more low end. The headphone output in the DUET is far better than the one built into my Mac. Is it worth it? Look at the files, consider the noise levels, the latency and decide for yourself. I suspect that something in the middle like a Focusrite 2i2 would have most of the benefits and less of the cost of the DUET.