ADC signal conditioning

Lucky

Hi all,

I am trying to use an analog to digital converter on the audio out RCA jacks of a T.V. As far as conditioning the audio signal before it gets to the ADC I have a few questions. I know a DC offset will have to be added to the signal and that some type of automatic gain control circuit needs to be used in order to keep the signal with in limits of the Vrange of the ADC. Does anybody have any suggestions on how to go about the AGC part? I know they make AGC ICs, but was wondering if something simpler was an option. Thanks

-I am also having a hard time finding a suitable AGC IC. They have variable gain amplifiers (VGA) but that is not automatic

kwinn

As far as I know the audio out signal is already at a fixed level suitable for input to an external mixer/amplifier or other device. For input to an ADC all that should be required is to add the DC offset and amplify or attenuate the signal so that the highest levels (during a commercial) is in range. Of course if you want to process the audio so you can hear the lowest levels in the program without having your eardrums shattered by the commercials, crappy theme music, etc. then you need to vary the gain/attenuation. You might want to consider a digital potentiometer for that.

Leon

I've never used AGC when sampling audio with an ADC. They are used in some situations, with a programmable gain amplifier, and implemented in software, but you won't need it. An anti-aliasing filter is used in most codecs, and that could be useful.