What is the test for obtaining a transcript of a witness' pre-trial statement?

In every case, however, the statute must be interpreted with a mind to the fact that only a substantially verbatim, not a precisely verbatim, recital of the witness' pre-trial oral statement is required; and the recording made of this statement of which the document sought may be either the original or a "transcription" need be only contemporaneously, not simultaneously made. Moreover, the statutory language should not be construed so narrowly as to lose sight of the congressional purposes to exclude the subjective impressions and opinions of the person making the report and to prevent the use of "statements to impeach a witness which could not fairly be said to be the witness' own," Palermo v. United States, supra, 360 U.S. at page 350, 79 S.Ct. at page 1223.