This was my testing procedure.
The lenses were tested on their own disconnected from the camera body since the shutter is built into Mamiya lenses. So I didn't have to deal with the reflex mirror and its noises. The camera wasn't needed for the test. Only the 4 lenses.
The tests were done with the mirror up knob on the lenses set to Manual. I cocked the shutter manually on the lens for each shutter speed test. Then I manually released it back to the shooting position. I then set the shutter to the setting I was going to test. Then I turned on the recorder and placed the camera adjacent to the cell phone. Then I released the shutter with a cable release to avoid extraneous sounds and vibrations. I also left the aperture to its widest.
I then emailed the recordings to my desktop and loaded each one into the Audacity program for analysis. As you can see in the above 4 samples, the slowest shutter speeds were the easiest to mark their length. The faster shutter tests became more difficult due to the "hash" and overlapping noise . So it was hard to tell when the shutter opened and closed on fast shutters. I guessed a lot on those. These lenses have T, 1 sec, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250 and 1/400. YOu can see the results on the handwritten charts above.