An analog signal that has been digitized and stored can never be returned to the original analog signal exactly as it was in analog form. The sampling rate (bitrate) and sampling width (number of bits) set the limit of how much information is lost. So remember always that all digitized signals have information loss, and all are therefore "lossy" systems. A compresion system that is "lossless" cannot overcome this limitation, it just uses a compression system that preserves the digital data without further data loss.

Even analog systems suffer from information loss. They all have a noise floor that describes the lower limit of their ability to store and reproduce a signal. Signals that are below that threshold are lost, or at least mofified by noise. Most analog systems suffer from outside noise sources too, like mechanical vibration and what not.

I felt the need to remind everyone about this. MPEG/JPEG compression is a lossy compresion system, that is true. But you can set the level of loss. If set low enough, there is less loss in the compression system than there is in the digitizing process. At that point, it's mute. Because of that, I'd suggest that all other factors (bitrate, sample width, etc) be considered, not just the compression system used.