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Re: Use of a laptop / sound card for field recording

Subject: Re: Use of a laptop / sound card for field recording
From: Mike Macaulay <>
Date: Fri, 11 Feb 2005 12:58:49 -0800
<pre style="margin: 0em;">I have used both PC's and notebooks with A/D cards, 
some from NI and
 some from other manufacturers. If you need multiple channel samples,
 you have to watch out for inter-channel sampling rate, for which some
 cards have larger time intervals than others. The fix then is to get a
 simultaneous sample-and-hold, which samples all channels at the time
 the first one is sampled (freezing the samples on all the others) and
 then fills the multiple channel buffers at a rate faster than the
 interval between within channel samples.  Noise can be controlled by
 using differential input; this provides effective noise cancellation
 but cuts the number of available channels in two (typical 8 channel
 cards are only 4 channel differential). A/D cards now can sample at
 mega-samples per second, but these are often only available in PCI
 internal card format. PCMCIA cards continue to improve in 
 <pre style="margin: 0em;">I suggest using USB2 or Firewire removable drives 
since these are much
 faster and larger capacity. The problem with removable disks is that
 they generally need more power than a notebook can provide. Also, many
 notebooks use low rpm drives -- 4400 or 5400 rpm -- and this slows
 their performance. Depending on the notebook, you can replace the
 internal disk with a faster and larger one.</pre><br>
 <pre style="margin: 0em;">As has been pointed out, many "Sound Cards" have 
issues associated
 with acquiring signals in the audio spectrum. These issues include
 low-frequency drop off, capacitor input (assumes signal is AC), and
 other "features" that make audio sound acceptable to our ears but may
 alter the basic signal. As a rule, A/D cards make no such compromises;
 their job is to record anything from DC to the Nyquist limit of their
 sampling rate and induce nothing on the signal amplitude.</pre><br>
 <pre style="margin: 0em;">Rugged notebooks are available, but the ruggedness 
add thousands of
 dollars to the price. These models can take being dropped and immersed
 and exposed to dust without much concern. The issue of power remains
 an issue. On boats or vehicles you can carry extra batteries. In fixed
 spots you can set up solar/battery systems, but when you have to
 travel light, then the CF memory recording systems will be the 
 <pre style="margin: 0em;">Mike Macaulay
 [EMAIL PROTECTED]</pre><br>
 <pre style="margin: 0em;">Michael C. Macaulay, Sr. Oceanographer
 Applied Physics Laboratory, University of Washington
 1013 NE 40th St., Seattle, WA 98105-6698
 206-543-7105; FAX 206-543-6785; [EMAIL PROTECTED]</pre><br>

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