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RE: how best to connect a hydrophone to a laptop?

Subject: RE: how best to connect a hydrophone to a laptop?
From: Eric Delory <>
Date: Thu, 15 Jan 2004 09:30:55 -0800
<tt>Hi all,</tt><br>
 <tt>I thought two notes could be added to the suggestions made about hard- and 
 software audio recording machines for bioacoustics, now that digital audio 
 is beating records at attractive prices.</tt><br>
 <tt>Watch out.</tt><br>
 <tt>1) On the hardware side:<br>
 I've come through an excellent audio acquisition board, famous brand, with 
 96kHz SR & 24 bit resolution, and was astonished that the device was 
 actually cutting at 20kHz. High end audio systems like the previously 
 mentioned Pro Tools Digi 002 have specs only until 20kHz (see , above which nothing is guaranteed and I would not bet 
 that they don't filter above 20kHz too to secure dynamic range and only use 
 the high SR to reduce the AD/DA converter distortion. High SR (96-192 kHz) 
 audio boards do not mean "ultrasound enabled" or "can record up to half the 
 sampling frequency".</tt><br>
 <tt>2) On the software side<br>
 Audio software generally provides a plethora of attractive filters, down-up 
 sampling, interpolation, file format conversion tools, etc... for which 
 very little is guaranteed or documented at "microscopic" level (phase 
 distortion, for example) and although to your ear and on your spectrogram 
 the job sounds and looks good, your data may be irreversibly unusable for 
 fine analysis, like vocalization pattern recognition etc... Lots of tricks 
 on audio softwares are pure and hardcore signal processing but meant for 
 audio, human hearing, that the manufacturer won't even want to disclose 
 information about when you need it.</tt><br>
 <tt>This is where, for example, on both hardware and software sides, 
 instrumentation brands find a niche on the acoustic market - and are not 
 always that expensive, why softwares like Ishmael were created (free, if i 
 remember), and why lots of bioacousticians work with their well-known, 
 regularly calibrated DAT machines (even if they sound old fashioned) or 
 rough ten year old A/D acquisition boards, and process everything under 
 Matlab - expensive or Octave -free!. The learning (and the initial expense) 
 is tougher but always worth it eventually.</tt><br>
 <tt>Still, an excellent audio recording station like a Pro Tools system may be 
 turned into a scientific instrument for some applications that find its 
 specs sufficient and adapted to the task. But, although i wish it were - 
 and I am thinking of getting one for my home-studio, it is not aimed for 
 acoustics but ... audio recordings, our human ears. Eventually, audio 
 systems are not designed to provide more precision or signal integrity than 
 what human hearing needs, and not the precision and integrity that your 
 analysis may find necessary.</tt><br>
 <pre style="margin: 
 Eric Delory
 Laboratori d'Aplicacions Bioacustiques
 D164, Escola Politécnica Superior d'Enginyeria de Vilanova i la Geltrú
 Universitat Politécnica de Catalunya
 Avda. Víctor Balaguer s/n
 08800 Vilanova i la Geltrú
 Barcelona, España.
 Tel. (34) 93 896 27 72
 Fax.(34) 93 896 77 00
 H/P.(34) 655 33 0196
 [EMAIL PROTECTED]</pre><br>

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