You can easily double-check the Control & Voice Channels by tuning into them as conventional frequencies and opening squelch, and then listening to them to hear if you are getting dropouts or audible interference. If you have bad receive, you'll have bad decode, regardless. The other side of that coin is, that the maunal adjustment(s) do absolutely nothing to fix reception issues. The adjustment(s) mentioned below must be done while you have good reception. There are the additional caveats explained further in this article. It is likely "the most important thing," besides good reception, of how well, the digital system, will be decoded. In some scanner models it is System/Site specific, in other models it is a hidden feature. There's three variants in the Menu to help for the "novice", the "intermediate," "advanced' users, at least try to enable a 'bit' better decoding than standard Auto settings. The P25 Threshold is a kind of "digital squelch setting". P25 digital decode threshold adjustments allow user to control of how digital system are decoded inside the scanner.