Originally Posted by lorriman
You may not need an app. the equalisation on older ipods was truly dreadull; distortion even at just a few dB's of extra bass. But newer devices have decent equalisation. Some equalisers do introduce aliasing, however. The rockbox equaliser did this, for example with very high frequency sound. You can test yours with a sine/tone sweep. As it goes beyond 15K Hz you hear lower frequency 'zipping' sounds.
How recent have you tested this? I know that newer builds have been changing the way they do interpolation, now using Hermite polynomials instead of simple linear interpolation. Saratoga pointed this out to me in a thread some time back. Aliasing is tied to the interpolation method, so as Rockbox migrates their interpolation method, this sort of thing might change.
I use Rockbox EQ often for lower quality headphones, and generally am satisfied. I really like the sound of the Onkyo app on iOS, though, especially when using its 64-bit setting. The EQ interface for the Onkyo app is not as good, though -- I prefer traditional parametric controls over a "draw your own curve" type interface.