OT: S/N-Ratio measurment - help

[Magnus Danielson]

From: Martin Czech <martin.czech at intermetall.de>
Subject: RE: OT: S/N-Ratio measurment  - help
Date: Tue, 8 Feb 2000 15:04:24 +0100 (MET)

> :::Don't forget the dirt that comes from the powersupply. 
> :::Digital and analog GNDs must meet at the edge connector, not at the mains
> :::GND terminal, some manufacturers don't even include on card regulators, etc. 
> :::(Look for a computer with star-grounding and linear PSU ;->) 
> :::Best thing to do would be to power the card from an extra linear PSU, or
> :::via a DC/DC convertor. And I wish they would float the in/outs, I get
> :::groundloops everytime I plug something into a soundcard.
> 
> The manufacturer must earth the chassis to protective earth, and as
> ISA bus cards are made that way they are, signal ground is protective
> earth then. A nice groundloop which is not improved by the fact that
> a PC is a HF sender, i.e. the whole chassis jumps up and down with
> the clock and it's subharmonics and other bands, since the connection
> to protective earth works for dc, not for these transients.

Actually, floating ground is a really stupid thing in EMC related issues, at
least most of the time. That the chassi ground is hardbonded to signal ground
with multipoint grounding rules is not a bad thing in that sence, but it does
create a nuicance for audio range signals.

> I'd like to test one of my audio transformers with my friend's PC,
> I guess much of the noise will go away then. Other problems
> may come up then, low frequency impedance and response?

A good audio transformer virtually cures some of these problems while not
taking too much out of the intended signal.

> I think the useable cards contain only the ISA interface and optical
> connectors to an external ADC box, with seperate supply.
> This way very high quality is available today.

Yeap, I also beleive this is a possible way.

> Isn't there any optical/coaxial SPDIF interface card on the market.
> It think so. Combine it with your portable DAT, or maybe a second
> hand DAT with broken mechanics (ADC still working), a lot more
> fun for the money.
> 
> Removing any kind of noise out of recordings is such a sh*t that
> allmost any effort is worth to avoid it right from the start.
> Been there and suffered a lot from *quick and dirty* recording.

Right. It is not too hard to get it right....

Cheers,
Magnus