I never really thought about this one. We have a bard who uses this and we let it continue.
After properly looking at it I think it works ...
Benefit: Whenever you are using bardic performance to create a spell-like or supernatural effect, allies within 30 feet of you deal an extra 1d6 points of sonic damage with successful weapon attacks ...
The effects of your bardic performance carry on, even after you have stopped performing.
...
Benefit: The bonuses and penalties from your bardic performance continue for 2 rounds after you cease performing. Any other requirement, such as range or specific conditions, must still be met for the effect to continue. If you begin a new bardic performance during this time, the effects of the previous performance immediately cease.
Because they both use the term "effect" I'm giving it the benefit of the doubt.
I'm probably not 100% un-biased though, so if anyone else wants to weigh in I'm open ...?
Discordant Voice is a feat not a bardic performance. Lingering Performance specifies that it extends the effects of your bardic performance.
Starting a bardic performance is a standard action, but it can be maintained each round as a free action. Changing a bardic performance from one effect to another requires the bard to stop the previous performance and start a new one as a standard action. A bardic performance cannot be disrupted, but it ends immediately if the bard is killed, paralyzed, stunned, knocked unconscious, or otherwise prevented from taking a free action to maintain it each round. A bard cannot have more than one bardic performance in effect at one time.
Discordant Voice only works when you are using a bardic performance. Since you cannot have more than one bardic performance active at the same time it is obviously not a bardic performance. If it were a bardic performance it would not work because that would mean you have two performances active at the same time.