Videomaker – Learn video production and editing, camera reviews › Forums › Technique › Miscellaneous Techniques › Defeat the AGC with 15KHz tone › It seems like you are prop
It seems like you are proposing a complex solution for a simple problem. The obvious answer is to turn off the AGC and use the camera’s manual volume controls. If you can’t do that, maybe it’s time to upgrade your camera.
Addressing your suggestion, your proposal may be more difficult than it seems. Basically, you are saying that a combination of a 15KHz tone and the mic audio would keep the AGC from raising its gain during quiet periods. That means that during quiet periods the 15KHz tone will be recorded at full volume on the tape. Note that the voice isn’t exactly being held constant, the sum of the mic audio and the tone are being held constant by the AGC adjusting the gain.
To try this you will need a good low distortion sine wave generator and a high quality mixer. Low distortion is essential because distortion of the sine wave will give rise to harmonic components that may be audible after going through the digitation process inside the camera. After all, during quiet periods, the 15KHz tone is being recorded at full volume because the AGC has brought it up to that.
The low pass post filter to remove the 15KHz tone from the audio output of the recorded program is probably not too critical in that 2nd or 3rd order filter with a 7KHz knee would probably reduce the 15KHz tone enough to prevent it from overloading downstream equipment.
By the time you buy a low distortion sine wave tone source, a low distortion mixer and a filter, you are well on your way to the price of a new camcorder with adjustable audio levels.