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Re: Data Acquistion Standards

On 14 Jun 01, at 15:43, Bradley Wood Libbey wrote:

> 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

         D A Q A R T A
Data AcQuisition And Real-Time Analysis
 Shareware from Interstellar Research