Legal Question in Civil Rights Law in California

Many uses of sound recordings are inadmissible in court -- if he recorded your voice without your consent, it won't be admissible, and he might have violated the law in making the recording. This could subject him to possibly being arrested or being sued by you for making the surreptitious recording, It depends on who was recorded and the circumstances under which the recording was made, facts you did not provide in your question.

Mr. Stone's answer regarding your voice is well stated.

You may also argue, if the the "voice evidence" is of another party, that the statements are hearsay and not admissible to prove the truth of the statements. In court you would raise such an objection.

Small claims judges are usually very quick to clarify that. You may wish to repost your question with more facts about the nature of the evidence.