Possibly defeat the audio AGC on your Sony or other cam?

[Vic Morris]

Possibly defeat the audio AGC on your Sony???

Has anyone had any luck defeating the audio AGC on Sony Mini-DV and Sony
Digital 8 camcorders?

With the 16bit two channel stereo, there is the potential for great sound...
what if you split the mic input with a y-adapter?

Say, have a MKE300 shotgun mic feeding the left channel and a constant mid
level tone feeding the right channel, coming from a portable MP3 player.

Would the constant tone on one channel keep the AGC at bay?

Then just take out that unwanted audio channel in your editing program...

Has anyone tried this? Anybody see any flaws in the setup?

Peace,
Vic Morris
http://vicmorris.blogspot.com

[Scott Dorsey]

Vic Morris > wrote:
>Possibly defeat the audio AGC on your Sony???
>
>Has anyone had any luck defeating the audio AGC on Sony Mini-DV and Sony
>Digital 8 camcorders?

There are some published modifications out there to disable the AGC circuit
and install a line-level input on some of the DV camcorders out there,
courtesy of the BBC. I don't know who is doing them, but you might try
asking on rec.arts.movies.production.sound for a pointer.

Be aware that without AGC, you will also need accurate metering, something
most camcorders are still sorely lacking in.

>With the 16bit two channel stereo, there is the potential for great sound...
>what if you split the mic input with a y-adapter?

Well, you're still in a box full of motors and digital electronics, so I
would not expect anything approaching the theoretical noise floor on these
things.

>Say, have a MKE300 shotgun mic feeding the left channel and a constant mid
>level tone feeding the right channel, coming from a portable MP3 player.
>
>Would the constant tone on one channel keep the AGC at bay?

Maybe, BUT what you are doing is going to be forcing the gain control down
to the lowest possible level, and then you're going to have to be recording
at a very low level as well. This may reduce the pumping but it sure is not
going to be good for your dynamic range.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Ty Ford]

On Sun, 18 Jul 2004 00:51:57 -0400, Vic Morris wrote
(in article >):

> Possibly defeat the audio AGC on your Sony???
>
> Has anyone had any luck defeating the audio AGC on Sony Mini-DV and Sony
> Digital 8 camcorders?
>
> With the 16bit two channel stereo, there is the potential for great sound...
> what if you split the mic input with a y-adapter?
>
> Say, have a MKE300 shotgun mic feeding the left channel and a constant mid
> level tone feeding the right channel, coming from a portable MP3 player.
>
> Would the constant tone on one channel keep the AGC at bay?
>
> Then just take out that unwanted audio channel in your editing program...
>
> Has anyone tried this? Anybody see any flaws in the setup?
>
> Peace,
> Vic Morris
> http://vicmorris.blogspot.com

1. Not all 16-bit stereo is the same quality.

2. Why not buy a camera with enough technology to allow you to dial out the
AGC?

3. I wonder what the crosstalk figures on sony mini cams are. Using tone on
one channel in an unbalanced audio section will usually result in crosstalk
problems.

4. AGC is only activated when the audio level rises above it's threshold. By
adding tone at a level that would activate it would be a pretty loud tone and
pretty likely to bleed. In that case, the ACG would be ON and do what you
don't want it to do.

5. Low level tone wouldn't really have any effect since it wouldn't trigger
the AGC.


Regards and have fun with that.

Ty Ford


-- Ty Ford's equipment reviews, audio samples, rates and other audiocentric
stuff are at http://home.comcast.net/~tyreeford

[Kurt Albershardt]

Ty Ford wrote:

> On Sun, 18 Jul 2004 00:51:57 -0400, Vic Morris wrote
> (in article >):
>
>
>> Would the constant tone on one channel keep the AGC at bay?
>> Then just take out that unwanted audio channel in your editing program...
>> Has anyone tried this? Anybody see any flaws in the setup?
>
>
> 3. I wonder what the crosstalk figures on sony mini cams are. Using tone on
> one channel in an unbalanced audio section will usually result in crosstalk
> problems.
>
> 4. AGC is only activated when the audio level rises above it's threshold. By
> adding tone at a level that would activate it would be a pretty loud tone and
> pretty likely to bleed. In that case, the ACG would be ON and do what you
> don't want it to do.
>
> 5. Low level tone wouldn't really have any effect since it wouldn't trigger
> the AGC.

I wonder if you could use something like a 30Hz or 40Hz tone? It would be easy enough to highpass in post and might do the trick...

[JoVee]

Kurt Albershardt at wrote on 7/18/04 4:21 PM:

>> 4. AGC is only activated when the audio level rises above it's threshold. By
>> adding tone at a level that would activate it would be a pretty loud tone and
>> pretty likely to bleed. In that case, the ACG would be ON and do what you
>> don't want it to do.
>>
>> 5. Low level tone wouldn't really have any effect since it wouldn't trigger
>> the AGC.
>
> I wonder if you could use something like a 30Hz or 40Hz tone? It would be
> easy enough to highpass in post and might do the trick...

some AGC's can/would actually try to TRACK a 30hz tone...!


--
John I-22
(that's 'I' for Initial...)
Recognising what's NOT worth your time, THAT'S the key.
--