1. Home
  2. Electronics Design
  3. Defeating audio AGC?

Defeating audio AGC?

[This may be a duplicate post. After posting it the first time on Cox, I saw that Cox may have been UDPed because of spam, so I'm posting it again on Octanews to make sure it gets out.]

This isn't really a design question as such, but I hope someone will have an idea about it.

I have an Canon Elura 100 miniDV camcorder, which has automatic gain control on audio. I'm sure Canon thought they were doing a good thing with this, but it causes motor noise to be picked up quite noticeably during times when the audio level is low and the gain is ramped up to the maximum.

This model also has an external mic input, but the mic needs to be a "self-powered" electret. So, I built a little amp for that, powered by a 9V battery. Unfortunately, it appears the AGC is still there. And while I don't get motor noise, it appears the amplifiers in the camera aren't exactly low-noise, so when they crank up looking for something to hear, Or it may be noise from my amp that gets amplified, but I don't hear that when I use this setup on the computer mic input.

Anyway, since I've already built this amplifier, I just wondered if there's anything I could add to its output that wouldn't be audible to humans, but would fake out the camera AGC. Or maybe center the output level a bit above ground - well, ok, that's not likely to work assuming the camera inputs go through capacitors.

Well, I don't have my hopes up on this, but just thought I would ask in case there was a solution.

Of course I could record the audio separately on another device, but that's a lot of trouble since the streams would have to be synced at some point.

Thanks for any ideas.

Reply to
George
Loading thread data ...

try a lower impedance to the input of the mic of the camera.

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
Reply to
Jamie

Not sure I uderstand what difference it would make. Anyway, the amp I built has a 100-ohm output impedance as it is. I thought that was already pretty low.

Reply to
George

Can you roll-off some of the low end? (I assume this is where the motor noise resides) Maybe by using a couple series .022uF capacitors?

-mpm

Reply to
mpm

The idea was to lower in the input to the camera in attempt to not allow the input to be so sensitive to white noise when gain was maxed out. or. Experiment with injecting high frequency audio to see if the gain loop will drop back. It's very possible the high freq will get removed in the cam further down the line.

--
"I\'m never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
Reply to
Jamie

mpm snipped-for-privacy@aol.com posted to sci.electronics.design:

I suspect that the issue is mechanical noise rather than electrical noise.

Reply to
JosephKK

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.