One of the pitfalls of audio testing is loudness between devices under test. One must be scrupulously careful to gain match anything you’re comparing to. If a new amplifier, even a dB or so difference in gain can make a noticeable performance change. And, you certainly don’t want to choose one piece of kit over another when a simple twist of the volume control can make this right again.
When we test various designs or wish to listen to the works of others it’s pretty easy to gain-match since we have access to a lot of fancy audio test equipment. You, dear reader, probably do not have that same access and so it can be a little more difficult.
You can often go to a manufacturer’s website and get their specs. There, you can see at a fixed frequency how much gain an amplifier has. If it’s off by dBs, then your next challenge would be how to compensate. With many preamps, such as our own, we specify our volume in predefined steps: 0.5dB for most of the range.
You can also gain match with a test disc and microphone setup. On my iPhone, I have several dB meter apps. Decibel X is one that’s worked well for me, but truth is, you can use just about anything and it’s fine. The key to gain matching is making sure the microphone is in exactly the same spot each time and the tone played is the same too. I still use the Stereophile test disc as my reference standard.
However you manage to gain match equipment, just make sure you do when evaluating for sound quality.