He puts the analogue gain up, takes off the digital gain and, well, that's it. It's exactly 3 years old at time of writing, ML was in very early stages of development yet using an external mic with 0db of digital gain, the sound is clean and very useable.

Now, before people jump on my back and start hitting me on the head with a monopod, repeating over and over 'it's the AGC', 'all DSLR's on-board sound is awful - record externally' etc, may I direct you to this video by the wonderful Dave Dugdale. I have tried with and without ML with no difference (thus seemingly eliminating the hack as the culprit - unless it was ML that screwed up my camera in the first place), so I am using Magic Lantern to try and get to the bottom of the problem as I can manually adjust analogue and digital gain with it enabled. The camera relies heavily on digital gain to get a decent level, which introduces a constant gain 'hiss'. I've run in to a major problem however and can't find a solution - the sound recordings are absolutely awful (see thread 'Audio Problems with Magic Lantern 2.3 & 60D' -, now at nearly 2.4k views, for an indication about how widespread this seems to be). All was well, I was excited to find out about Magic Lantern (especially the ability to change bitrate) so eagerly installed it and went off on jobs.

I recently bought a second-hand Canon 60D. Thanks in advance for taking the time to look at this.

Magic lantern canon 60d issues