Yes, you can. You can do this very easily and for free using a program called dbPoweramp. dBpoweramp

How much to compress depends on the type of music. I would not go too low on classical - it really effects the sound. 128 is the normal "low" setting. 192 is a "mid-range" setting and 320 is the "audiophile" setting. So you see you are already near the low end. You could go as low as 96, but I would not go any lower than than.

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Fredrick T. Greco
Senior Pastor, Christ Church PCA (Katy, TX)
Christ Church Blog

"The heart is the main thing in true religion...It is the hinge and turning-point in the condition of man's soul. If the heart is alive to God and quickened by the Spirit, the man is a living Christian. If the heart is dead and has not the Spirit, the man is dead before God." (J.C. Ryle)