A Case in Proof
Proving one's case in court involves more than just stating the facts. Unless and until the judge reasonably concludes the evidence you want to admit is admissible, no one's stating anything.
Myriad rules now govern admissibility, including the Federal Rules of Evidence (FRE), the U.S. Constitution, and acts of Congress. While under common law, evidence had to be pristine before it could be admissible, American law evolved, embracing the principle that more is better. The FRE mandate admits evidence with defects bearing on weight and not admissibility as long as the evidence is relevant and authentic, barring other means to prohibit its introduction.
Relevancy is defined by a broad standard. The FRE state that "evidence is relevant when the evidence makes the occurrence of a fact that is of consequence to the determination of the action more probable or less probable than it would be without the evidence." This is a pretty low threshold. As long as the evidence is material (a fact of consequence) and relevant (makes it more probable or less probable), under this standard, it's coming in.
Evidence is authentic when the party seeking to introduce it into evidence can support a finding that it is what he says it is. This can be done several ways. A witness can testify to its authenticity or a chain of custody can be established. In the case of recordings, even if the recordings contain anomalies, the anomalies will not be dispositive if the proponents can provide an explanation.
Once the judge believes a reasonable jury could find a recording to be authentic, it becomes admissible. After it is admitted, if the opposing party still has a genuine concern as to its authenticity, the burden shifts to the opponent to prove the recording is not authentic. This may be accomplished through cross-examination, rebuttal witnesses, closing arguments, and jury instructions.