Thanks very much to you and to Bob Paddock. I haven't
started actually building anything yet, but I hope I can either find a
single-chip audio AGC device with a wide input level range
or an amplifier with a voltage-controlled gain adjustment kind of like
the old LM370. I do have some of those, but they add distortion to
the audio and, if I remember correctly, one needs to cascade a pair of
them to get 10 or 20 DB of gain adjustment. I haven't looked at those
in a while, but I remember that they do work all be it roughly.
If one has an audio amplifier with a DC gain adjust, then all
that's left is to rectify the audio and filter that signal to produce
the AGC voltage.
I think the NE571's virtue was it had a rectifier on board and
the adjustable gain stages all in one chip.
The other possibility is a more complex arrangement using a
PIC that contains an A/D converter plus a digital pot. I don't doubt
that that can be made to work, but it will be slightly more expensive
both in parts count and in their actual cost. It will probably need
lots of tweaking to get it right, also.
Declan Moriarty writes:
>On Tue, Feb 17, 2004 at 07:59:19AM -0800, Martin McCormick enlightened us thus
>ly
>> Someone recently suggested using a NE570/571 compander chip
>> for building an audio AGC circuit. This chip has been around for
>> about 25 years or so and has seen wide-spread use.
>>
>> Is it still considered a good choice if one needs level
>> compression or expansion or is there a more state of the art chip?
>>
>> Thank you, as always.
>>
>
>It's not my strong area, but I am aware that compression algorithms have
>improved over the years; IIRC, the Dolby standard was revised with more
>DB of compression/expansion. I would check for later devices.
>
>A good check is to see if it is available everywhere or available in
>smt. Otherwise you can bet there is better out there.
>
> With Best Regards,
>
> Declan Moriarty.
>
>--
>Author: Declan Moriarty
> INET: [EMAIL PROTECTED]
>
>Fat City Hosting, San Diego, California -- http://www.fatcity.com
>---------------------------------------------------------------------
>To REMOVE yourself from this mailing list, send an E-Mail message
>to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in
>the message BODY, include a line containing: UNSUB CHIPDIR-L
>(or the name of mailing list you want to be removed from). You may
>also send the HELP command for other information (like subscribing).
>
--
Author: Martin McCormick
INET: [EMAIL PROTECTED]
Fat City Hosting, San Diego, California -- http://www.fatcity.com
---------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB CHIPDIR-L
(or the name of mailing list you want to be removed from). You may
also send the HELP command for other information (like subscribing).
