There are two paths to resolving mix conundrums. Before attempting either, walk out of the sanctuary for five minutes so your ears can re-boot.
Check the channels- The mix may not sound right because of a single channel or multiple channels. Mute a channel, listen for impact, and then un-mute and move to the next channel. If the problem is related to a single channel, this method will identify it.
Kill group and board-wide Effects Gates, compressors and other effects can be applied to groups or a board-wide mix. Turn off these features one at a time. Listen to the mix difference.
Look for conflict - Look for cross-channel conflict. A mixing rule of thumb is each instrument / vocal should own their defining frequencies. Two channels should not be competing for the same defining frequencies. I have inadvertently boosted the same frequency area in two different instruments. It wasn’t until reviewing the changes that I realized my bone-headed mistake.
- Rebuild it from scratch
Turn off effects; reverbs, compressors, gates, etc. Re-set channel EQ’s. Push faders to unity and check all channel gains. Think clean slate. Balance the channels so instruments and vocals sit in the right spaces. Clean up channels; notch out those offending frequencies. From here, use YOUR standard mixing process. For example, add in gating before setting channel EQ’s. Or, set the channel EQ’s and then use gating. Use your standard process.
Sometimes a mix doesn’t come together. The problem can be a single mis-mixed channel, conflicting channels, group or board-wide problems, or a foundational mixing mistake. Isolate the potential problem area and listen for a dramatic difference. Once the area is identified, work on a solution. If that doesn’t work, rebuild the mix. Just make sure to first reset your ears by spending five minutes outside the sanctuary, this cannot be emphasized enough.