I have a 2012 Retina MacBook Pro running Arch Linux with GNOME. Normally, I listen to music using the analog audio I/O interface -- the 3.5mm socket.
Recently, I had to attach a USB microphone to the laptop. While doing that, I used the microphone's built-in 3.5mm socket to monitor the sound I was recording with lower latency and less distortion than what the laptop's internal amplifier, and the backing software, would produce. Because of this, I went into GNOME's sound options and updated the audio output profile to digial, which allowed me to pipe system sounds through the mic and into my headphones while I was monitoring the audio received by the microphone.
After switching back to using the 3.5mm socket on my laptop and reverting the audio output profile to analog (the only option available without the mic), the outputted audio's really distorted. After some tinkering using the ALSA mixer and reproduction of the issue on the laptop's main speakers, I've concluded that the issue is that outputting audio to my headphones now results in the bass part of the spectrum being cut off completely, resulting in a tinny, distorted, and almost downsampled effect.
Unfortunately, I haven't found any settings allowing me to tweak the bass response for the 3.5mm out.
Where can I do this system-wide?