Nope, it does not lower the trebles, neither does the bass. It doesn't add bass or trebles either, there is no cables that can do it....only "in-efficient or efficient" cables, and Pure silver is more "Efficient". Therefore, more air, and extensions can be observed. Probably due to this extensions efficient, the trebles has more texture, and smoother. It just sounds better period.
Personal opinion on my side, quality pure silver is the best of all cables. But I will stop here in the cables science kind of things. So, for anyone that asked. This is my personal opinions and experiences. Have fun picking your cables out