Hi,
so tone controls and EQ generally has had a bad reputation in HiFi for a long time - many pre-amps don't have tone controls at all.
All analog EQ, including tone controls, graphic and parametric equalisers, obviously muck with phase and group delay.
Not always in a bad way though - a parametric EQ used to tame a peak in room response will fix amplitude and phase response for the better, if the EQ is applied to fix a "minimum phase" peak.
That's not the reason for this post though...
Assuming a DSP based setup (MiniDSP, DEQX, whatever), and you've got the room under control with treatment and minimum phase EQ as required...and you want to tweak the bass or treble on a particular song or album...
...in a DSP world, why wouldn't this EQ be linear phase?
I'm unsure about MiniDSP and others, but I'm pretty sure that the DEQX EQ on the remote is minimum phase, not linear phase ( @artaudio ?).
These days all digital mixers (Digital Audio Workstations - DAWs) have the option of applying EQ in either minimum phase or linear phase, and there's reasons for choosing either one depending on the scenario.
But in a home audio context using DSP, why aren't tone controls always linear phase?
cheers,
Mike