AT&T DSL causing static on VOIP line

We recently changed from Comcast inteet to AT&T DSL. Since then we're having static on our phone line, which is a Vonage VOIP line. I'm assuming I need a filter, but I'm not sure where to put it since the phone line doesn't actually plug into the wall. Should the filter still go between the wall and the AT&T line? Or between the phone line and the Vonage modem? Or between the Vonage modem and the AT&T modem? And is it just a single filter that I need, or one with a splitter? Thanks

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