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Even with the AGC Disable technique, there are limitations in usability and
performance. The technique greatly improves signal to noise performance, taking
what was unusable audio, and providing you with something that you can work
with. But, it generally will not provide as high quality signal-to-noise performance
compared to a camera which already has manual controls. Additionally, there is a
good chance that you will have to abandon one of your recording tracks (the
camera’s right channel where the AGC Disable signal is routed). If you have not
yet selected a camera, we recommend that you consider one which already has
manual control of its audio.
Tone
The TONE setting injects a ~20KHz tone into the right recording track of the
camera.
This frequency is selected since it is beyond the audible range for most people,
and is an attempt to continue to use the camera’s right track for recording. This
may work OK on some cameras, and may not work at all on other cameras.
Continued use of the right recording track depends on the camera’s Nyquist Anti-
Aliasing Low-Pass Filter to be working extremely effectively. Otherwise, the
inaudible ~20KHz tone can produce aliased artifacts in the audio band. You will
need to run tests to validate the effectiveness of this approach with your
equipment. Evaluation of these tests must be done with the clip pulled into your
computer or with playback monitoring, since the headphone monitoring takes
place before the recording device.
If the evaluation of recorded audio is not to your satisfaction, then you will either
abandon the right recording track while using the TONE, or use the Safety Mode –
NOISE approach. In either case, if you are using right channel microphones
(XLR-R or RING-R), then you will use the PAN TO L switch to route those mics to
the clean recording channel (left).
If you are going attempt to use the right recording track, then you should test this
out before each shot. Some AGC algorithms which not only change their gain
settings, but also play around with filter roll-off frequency settings. This not only
effects aliasing which can produce in-band tone effects, but also creates audible
pops and clicks as the parameters get adjusted by the firmware.