I’m in the process of developing a listening test for a school project. The goal of the project is to develop system for evaluating listener skills on a predefined set of listening material. I plan to do this using the ABX methodology and I was wondering if anyone could give me some pointers on artificially introducing various types of distortion into my reference material.

Ideally, I’d like to modify the tracks such that they approximate the response of slightly different audio playback systems. Again, I’m looking for ways to introduce subtle realistic tonal imbalances, colorations, changes in articulation, etc.

Thanks

try Distorder, you can add various types of distortions and listen in real time, it also includes an ABX tester. It's easy to use.
Other softwares are available at same website to listen to some other audio effects (phase distortion, box diffraction, early reflections, room modes,...)

Latest edition of Fastl & Zwicker 'Psychoacoustics' has a CD with samples and there are some distortions on it.