Ray West (Consultancy)
| Microphone mount|
The inbuilt microphone, and automatic volume gain control (AGC) combination in most small video cameras combine to amplify the motor noise during quiet scenes. Many of these cameras do not have the facility for switching off AGC.
Using an external camera mounted microphone will only slightly reduce this noise, since the microphone mount will serve to mechanically transfer the camera vibration to the microphone. Also, for many of the small pocket cameras, such as the Sony PC7 and PC10, the mounting shoe is close to the rear of the camera, which means that mounting a microphone directly to this shoe prevents the use of the viewfinder.
We have developed a vibration absorbing sandwich material which succesfully prevents the transfer of most of the mechanical noise. The microphone mounting point is shifted forward so that the viewfinder can be used, and it is also raised so that the front of many microphones is outside the normal field of view of the lens (unless you use a windsock, or ultra wide angle lense).
The screen shot shows the waveforms of the audio tracks recorded from a PC7 camera (sorry about the quality, the photo was taken with a small digital camera straight from the computer monitor!). The top pair of tracks is for a microphone mounted on our adapter, whereas the bottom pair is for the same microphone mounted directly to the camera shoe. I have tried to ensure that the background ambient sound was the same for both recordings. The tracks consist of a short period of speech, followed by silence. It can be clearly seen that the bottom pair of tracks have much more backgound noise, as compared with the upper tracks.
Both recordings were passed into Sound Forge, for the purposes of viewing the sound files on screen, and absolutely no editing has taken place.