Instrument or line level for recording amplifier through headphone jack?

Question

I just got a digital combo amplifier and the only outputs it has are USB and a headphone jack. I am trying to record it by using a 3.5 mm to dual 1/4 inch adapter and plugging it into my interface. The USB out does not work well because I already have an audio interface.

My question is do I need to engage the Instrument level button on my interface?

I am not familiar with how line/inst level and things of that nature work. I read somewhere that impedance can affect sound quality. I want the best quality I can get although this isn't the optimal setup.

Hope this is not too confusing, Thanks.

Answer 1

As you said, that's a story of impedance: in short instrument level is generally used when the signal is coming from a high impedance source (guitar pickups) and the line level for low impedance or preamplified sources (DI, electronic keyboard and so on). The main reason for these two levels is that a high impedance will have an hard time driving a low impedance input (you can have a look at impedance adaptation for instance) hence resulting in very low levels of sound, resulting in more noise with respect to the signal.

The headphone output is designed to drive headphones (hence the name) and headphones have usually fairly low impedance (ranging from a few ohms to a few hundreds). Furthermore, this is coming from an amplifier which surely can provide the current to drive a line input so..

TL:Dr

You can safely put it in the line input and this is how, in theory, you'll achieve the best sound.