I’m an amateur guitar player starting in the world of audio recording with a simple objective: record a nylon string acoustic guitar at a decent quality.
Using a SHURE PG-48 connected to a Focusrite Scarlett 2 I noticed the recording levels are low, even after increasing levels in the interface controls.
I’d like to know if buying a SHURE SM-57 would increase the audio recording level or if it would be better to invest in a pre-amplifier.
Getting a SM57 will not help. According to the datasheets, they are about the same sensitivity (the SM57 actually is slightly less sensitive).
The problem you have is that your Scarlett probably has to little amplification (unless you have the 4th generation which has more gain).
Your options would either be to get an amplifier or select a different type of mic. As to amplifiers there are a number of "Cloudlifter" type of inline preamps to select from quite a few brands.
I would however suggest you get a pencil condenser microphone instead. The cost is about the same and the higher sensitivity will work with your interface. I find it difficult to recommende exact types as I have not tried very many in the budget range lately. This youtube might indicate one type:
