[PLUG] Microphones

Keith Lofstrom keithl at kl-ic.com
Mon Oct 23 17:07:37 UTC 2006


On Sun, Oct 22, 2006 at 07:13:12PM -0700, John Jason Jordan wrote:
> I need a microphone to record speech clips in Phonetics class. The
> usual telephone quality microphones are not high enough quality, but I
> don't need the kind of microphone they'd use to record a symphony.
> Should be unidirectional and noise-cancelling. 
> 
> I bought one today at Radio Shack, but will have to take it back
> because it doesn't put out enough juice to make a loud enough recording
> on my Compaq R3240 notebook with Ubuntu amd-64 Dapper. I cranked all
> the sliders to the max, but it was just not loud enough. For the
> record, the specs on the Radio Shack microphone are:
> 
> 	60-16KHz frequency response (a sheet inside 
> 		had a graph which was fairly flat) 
> 	Impedance 500 ohms + or - 30%
> 	Sensitivity -75 dB + or - 3 dB
...

This may be an electrical, not a software problem.  Most laptop
microphone inputs to laptops are designed to work with "electret"
microphones - these mimic the old-style capacitance microphones,
and have an internal amplifier requiring power and produce far
more signal than an unamplified microphone does.  You can check
my hypothesis by plugging your soon-to-be-returned microphone
into another laptop, perhaps at Radio Shack.  

What to do?  Perhaps a microphone pre-amplifier before the signal
goes into the laptop - this allows you to use the best microphones.
Otherwise, look around (perhaps on the web) for microphones designed
to work with laptops.  I think, but I'm not sure, that microphones
designed for cassette recorders have similar behavior.  

There are people in PLUG that know a lot more about microphones
than I do.

Keith

-- 
Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs



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