VST/AU developer DDMF released DirectionalEQ for AUv3 on iOS. This "stereo-field wizard" EQ lets you treat all directions of the stereo field independently. That is some seriously granular control. Thanks to reader yactre for alerting me to this one! There's no demo yet, but I look forward to seeing the power of this app in action.
DirectionalEQ iTunes Description:Traditional EQs influence the spectrum of the whole stereo field simultaneously. L/R or Mid-Side-EQs allow you to treat the two channels or the mid and the side signal simultaneously. DirectionalEQ takes this concept one big step further: now you can equalize all directions in the stereo field independently! With five bands, each of them providing state-of-the-art filter types (including 64 bit processing and 2x oversampling) plus the unique ability to specify the direction in which the channel is operational. So you need more bass at 2 o’clock, less midrange at 11 o’clock and a bit more treble from the left? No problem at all, that’s exactly what this EQ has been made for!
This app is intended to work as an Audio Unit plugin within a compatible host app like Garageband, Cubasis or Auria.
Update: There's already a thesoundtestroom demo! Thanks to Tom for commenting here with it.