Let me suggest a project for you that I think will fit with what you've learned and with the scope of the project, as far as I can judge it: Denoising of audio signals by spectral subtraction techniques.
The basic method is relatively simple. You need to cut your signal into overlappling blocks, you window each block, compute an FFT, and modify the magnitude of the FFT coefficients according to the estimated SNR in that frequency bin. High SNR means no modification, low SNR means attenuation by some gain factor $g$ satisfying $0<g<1$. For reconstructing the signal you combine the overlapping blocks (after IFFT) and you use the phase of the noisy signal, so only the magnitude is modified.
The nice thing about it is the simplicity of the basic method, but also that you can tweak a lot of things (gain computation, SNR estimation, etc.) to improve the perceptive quality of the denoised signal. If you do it in a very simplistic way you'll hear many artefacts, such as musical noise.
Also have a look at this and this answer for some more information on spectral subtraction.