Re: Data Acquistion Standards (Bob Masta )

Subject: Re: Data Acquistion Standards
From:    Bob Masta  <masta(at)UMICH.EDU>
Date:    Fri, 15 Jun 2001 07:54:22 -0400

On 14 Jun 01, at 15:43, Bradley Wood Libbey wrote: <snip> > > > However, I am concerned about noise. I suspect that a majority of the > noise actually exists as acoustic energy, but I don't want my measurement > system to be adding to this. The first possible source of noise is from > aliased high frequency signals. What is the standard in auditory research > for antialiasing filters? If they are necessary, do most researchers use > stand alone filters or do they simply acquire digital data on acquisition > systems with built in filters? > Probably not the anti-alias filters, because there is rarely much energy above 20 kHz in the first place, and because the filters in a modern sound card are usually pretty effective. (Better than many pricey stand-alone lab-type filters of only a few years ago.) > Secondly is the analog circuitry or the analog to digital converter > noisier on an inexpensive card than on a "professional" acquisition > system? In conjunction with this, the card I am using requires a low > voltage input (making the card susceptible to peak clipping), this isn't a > problem when one considers 16 bits of dynamic range is available, all I > need to do is turn down the gain stage on the preamplifier. However, some > of this range is used up by the internal circuitry noise floor. I'm > either cutting the peaks or burying the quiet in noise. In other words > limiting my dynamic range. > You might want to compare different sound card specs at The guy who runs this site does meticulous measurements. Check out the signal-to-noise numbers for your card's listing, and compare to the rest. Note that you may need to know what chipset your card uses, if it's not a "name brand" card. Hope this helps! Robert Masta tech(at) D A Q A R T A Data AcQuisition And Real-Time Analysis Shareware from Interstellar Research

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