Re: Max input level of a PC soundcard?

Late at night, by candle light, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> penned this immortal opus:

Rich Grise wrote:

On Tue, 03 Jul 2007 12:47:29 -0700, Joerg wrote:


Hello Folks,

What's the max for soundcards? I have read specs of some where it says
22dbu which sounds wrong to me. A Via AC'97 I have seems to max out at
10mV RMS but no clue if that is a standard. There was no data*** on the
Via Technologies site. Also, anyone know the "frying level" where it would
go kaputt?

The motivation here is that I want to build a "noise sniffer" preamp.
20-40dB or so, plain old transistors. Here's hoping I'll get by with a
single AAA alkaline as the supply because that would allow a pen type
enclosure.


I'd say it should be good for "line in" levels at the "line in" input. ;-)

I've heard somewhere that this can go to .7 or 1VRMS; I'm sure you or
someone could look up the standard for "audio line level" or some such.
If you're building a 20-40dB preamp, then you could just clamp its
output at 1.4VPk or so if you're paranoid or anything. ;-)


Hmm, that would mean I need two AAA cells. Dang. But for some reason my
card starts to clip at 10mVrms. Thing is, I will use that on other
people's (client's) PCs as well so I want to play it safe.

No idea why mine clips so early. Maybe they have some kind of PGA on
there. Probably buried in a driver and there is next to nothing in
documentation. In the good old days PCs were extensively documented.
Nowadays you get a packing list and numerous lawyer pages, that's it.

The mic input is a lot more sensitive than the line input. BTDT, you
need to open up the advanced sound controls and select the active
input. Most laptops have only mic inputs, tip is signal and ring is
power (5 Vdc) so if you nees stereo inputs you're in a bind. Whichever
you choose make sure to select "no sound" unless you want it fed back
to the output.

Download Winscope or something similar and generate externally a
signal and watch when it starts to clip.

- YD.

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