Said stenographers shall be under the control and direction of the prosecuting attorney of the said county, and it shall be the duty of such stenographers to be present at all preliminary examinations when so requested by the prosecuting attorney, to take and transcribe the testimony of all such witnesses in said examination, and to certify the same as true and correct, which said certificate shall be sufficient proof of the correctness of said depositions, the reading of the same to or by the witness and the signing of the same by the witness being hereby dispensed with. Said stenographers shall also perform such other duties as may be required by the prosecuting attorney in the conduct of his office, and other county business. Nothing in this section shall be construed to provide an exclusive procedure for the taking of testimony at preliminary examinations, and such testimony may be taken by means of a mechanical recording device if the committing magistrate shall so order. In the event such mechanical recording device is used, one of the county stenographers shall upon completion of the hearing forthwith transcribe such testimony and certify the same to be true and correct as elsewhere in this section provided, and such certificate shall be sufficient proof of the correctness of such transcript and depositions and the reading of the same and signing of same by witnesses is hereby dispensed with.