Re: Devices for recording and impulse response measurements: revised version (UNCLASSIFIED)

[Bob Masta <audio@xxxxxxxxxxx>]

Angelique:

My Daqarta for Windows software does the basic operations 
you mention, using a standard Windows sound card (which can 
be a USB type).  It includes an Auto-Calibration facility 
to calibrate the mixer attenuator steps via a loop-back 
cable, after which you must perform a single full-scale 
range calibration on each line or output.  That will allow 
Daqarta to display absolute Volts.  If you want to see SPL, 
you need to supply a frequency response calibration curve 
for the microphone and/or speaker involved. (A simple text 
file is OK, or you can measure it with Daqarta.)  

Sound cards in general don't respond down to DC, and few 
even go down to 1 Hz.  However, if I understand your needs 
correctly, you are not concerned about continuous 1 Hz 
tones, but only impulses.  In that case, the sound card's 
coupling capacitors will pass brief waveforms just fine; I 
don't think you will have any problems there. 

145 dB SPL is rather a lot to capture without distortion.
I don't recall exact numbers, but I think this will require 
a small condenser mic, maybe 1/8 inch.  (Smaller mics 
handle higher SPL.)

Daqarta can do real-time waveform, spectrum, or spectrogram 
analysis.  It can capture impulses and can perform 
synchronous waveform averaging to reduce noise.  HOWEVER, 
it does not at this time have a built-in MLS facility.  
Spectra are limited to 1024 samples (512 lines) but there 
is a special interpolation option that can read a peak's 
amplitude and frequency with resolution similar to a 64K 
FFT.

You can supply weighting curves to make specific 
measurements. (An A-weighting curve is supplied in the 
package.)  You can set the cursor readouts to Sigma mode to 
read the RMS energy or power (including SPL) between any 
two frequencies.  There is also a large-readout Voltmeter 
option with a Peak mode, and you can set its dB reference 
for relative measurements.

There is an extensive Help system built in (several hundred 
pages), and a complete copy in conventional HTML pages is 
available to browse on the Daqarta site.  

I'd be glad to answer any specific questions.

Best regards,


=================================================
On 2 Nov 2007 at 15:13, Scharine, Angelique (Civ,ARL/ wrote:

> Classification:  UNCLASSIFIED 
> Caveats: NONE
> 
> I've gotten several very helpful suggestions - but so far, I'm only
> clearer on what we need - not necessarily on what to get! I'm hoping
> that if I clarify and revise my original request for suggestions, that
> some of the suggestions will be nearer to what we need. 
> 
> We're looking for a portable system or two portable systems to do the
> following tasks:
> 
> 1. Record sounds in the environment, including weaponfire at levels of
> approximately 145 dB SPL (peak), and do real-time analysis, including
> measurement of various kinds of SPLS.
> 
> 2. Record (binaural) impulse responses, mostly for the creation of
> virtual environments, but also for characterization of research
> laboratories, etc.
> 
> We have quality microphones, loudspeakers and amps that should suffice
> in most cases, although specific considerations and suggestions are
> welcome. 
> 
> What we are really looking for is a user friendly software package that
> does the real-time analysis and recording and an external sound card to
> use with a laptop. Ideally, this system could be calibrated so that the
> software gives absolute values - but this isn't essential. Our current
> system does allow for this. However, when used for recording of very
> loud sounds, there seems to be no way to turn the autorange feature off,
> which means that the resulting recordings are severely clipped. 
> 
> We've gotten some good suggestions for the room acoustics features
> described in #2, but I'd like to be sure that we cannot get a single
> system that will do both tasks before proceeding.
> 
> Thanks again for the useful suggestions!
> Angelique
> 
> They laughed when I said I was going to be a comedian. They're not
> laughing now. -Bob Monkhouse, comedian (1928-2003)
> 
> Angelique Scharine PhD
> Army Research Lab - HRED
> AMSRD-ARL-HR-SD
> APG, MD 21005-5425
>  
> (410) 278-5957 (landline)
> 298-5957 (dsn)
> (410) 278-3587 (fax)
> 
> Classification:  UNCLASSIFIED 
> Caveats: NONE

Bob Masta
 
            D A Q A R T A
Data AcQuisition And Real-Time Analysis
           www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!