David Drumm, a guest blogger on the Jonathan Turley Blog, addresses this question in the context of interviews by FBI agents. Why the FBI Doesn't Record Interrogations (Jonathan Turley Blog 5/11/13), here. He starts off:
At a time when recording a conversation is as easy as whipping out a cellphone or iPod, the FBI policy on electronic recording of witness interviews is: “agents may not electronically record confessions or interviews, openly or surreptitiously, unless authorized by the SAC or his or her designee.” Instead FBI agents take notes and later type up a summary report called a form 302. The interview takes place with two FBI agents and the single interviewee. The FBI has eschewed the objective for the subjective.Mr. Drumm then discusses the policy, its rationale and problems that have arisen in the Form 302 context and offers a very good video discussion by a lawyer named Harvey Silvergate. I strongly recommend that you read Mr. Drumm's blog and watch the video (and for those with the time, the comments to Mr. Drumm's guest blog are pretty good also).
The bottom line is that uncounseled interviews are risky business, which is, of course, why CI agents like surprise uncounseled interviews. And even counseled interviews are risky. Although there is no iron-clad rule, the better part of wisdom in an interview is to insist upon a voice recording or, if refused and the taxpayer still wants to participate in the interview (properly counseled, of course), to have two witnesses other than the taxpayer present in the interview to take notes that can be incorporated in a memorandum and attested by both of the witnesses.