Lab 4 is the "Volume" folder and it modifies the volume of an audio file, where INPUT.wav is the name of an original audio file and OUTPUT.wav is the name of an audio file with a volume that has been scaled by the given factor. The "Filter" folder is part of problem set 4, it is a program that applies filters to BMPs, where IMAGE.bmp is the name of an image file and REFLECTED.bmp is the name given to an output image file, now reflected. "Recover" is also part of problem set 4, it is a program that recovers JPEGs from a forensic image.