Possible fixes for the problem in the order I would do them. This is
not an uncommon problem for any microphone system.
1. Make sure the ground connections on your cables are well attached.
2. Make sure the mic cable is a high quality cable with a good shield.
3. Keep your mic cable as short as possible.
4. Loop your mic cable to form a small coil near to the recorder
using sandwitch ties to form the coil.
5. Add a Toroidal Core on your mic cable close to the recorder.
6. Add a .01 capacitor across the mic cable at the connector of the
recorder.
7. Go to a balanced microphone for the dish.
Rich Peet
--- In Dudley Edmondson
<> wrote:
>=20=20=20=20
> In recent months I have experience a strange thing with my HHB
portadsic
> recorder and parabolic stereo DAT mic.
>
> When I am recording bird audio near a resident or near city limits=20
I can
> hear a low frequency hum or buzz with music or voices in the
background.
> What I am picking up is no doubt a local radio station. In fact
once I
> heard the station say it call letters.....OLDIES 107 FM....... It
is not
> super loud or anything it just at a sound level that gets picked up
in any
> recording you make BUT not loud enough to overshadow the subject
source.
> But Just loud enough to be heard during moments of silence during a
> recording
>
> What the heck would make my recording set pick up radio stations??=20
Has
> anyone else had this problem. This sounds crazy to me and NO there
are no
> voices in my head........
>
> Dudley Edmondson
> Duluth,MN
________________________________________________________________________
________________________________________________________________________
>From Tue Mar 8 18:23:27 2005
Message: 1
Date: Sun, 16 Mar 2003 13:26:18 +0100
From: Gianni Pavan <>
Subject: Re: freq and time resolution in sonogram software on PC
In the windows software I developed (see previous message or the page
http://www.unipv.it/cibra/softw.html) the time resolution one can get in
real-time depends on the sampling rate (up to 192 kHz on standard windows
boards), on the number of channels (1 or 2), on the chosen fftsize (512 to=
16384), on the step among consecutive transforms (2 samples up to the
chosen fftsize) and, of course, on the available processing power. The
window length (16 samples to fftsize) and shape (I like gaussian and
kaiser-bessel) is not relevant for computation time. The computation
efficiency can be slightly modified by setting a proper data transfer
blocksize which affects the latency of the display.
Very few programs allows to modify all these parameters to get the desired=
frequency-time resolution in real-time operation.
Jus to make an example, on a PIII 500 portable I can get in realtime:
1 channel at 48 kHz sampling with FFT 512, Window size 256 (5.33 ms, about=
2.6 ms after weighting) and scan step 96 samples (2ms).
On a PIV 1.6 GHz laptop I can get the same real-time resolution with two
channels at 96 kHz!
In file analysis mode any possible frequency-time resolution can be easily=
obtained, of course the results on real signals are always conditioned by
the frequency-time undetermination principle. An useful solution, in some
cases, could be to overlay a zero-crossing plot (I'll implement it soon).
The display shows how much "cpu free time" is left after each transform.
This free time can be used by other processes (including saving to disk)
without affecting the spectrogram display or the continuity of the data
flow. The software has been developed to be safe and to warn the user if
something is going wrong, i.e. if the program is dropping samples... If
everything is set properly, the program can work continuously for days and=
weeks without dropping a sample! I use it for surveys to record marine
mammals. Surveys may be weeks long and the recording is made on 1 hour long=
files with automatic change of disk when one is filled (I normally have a
RAID array with 4 to 8 disks 80 to 200 GB each).
My software plots on linear freq. scale and now I'll try to add a log scale=
.
A nice feature, available with fftsize greater than 512, is the ability to=
zoom on a frequency band and to move in real-time the zooming window. This=
is useful, for example, to look in detail to low frequencies only (i.e. for=
large whales) or to high ones (i.e. for echolocating dolphins... or bats if=
in air).
Gianni
--------------------------------------------------------------
Gianni Pavan
Email
Centro Interdisciplinare di Bioacustica e Ricerche Ambientali
Universita' degli Studi di Pavia
Via Taramelli 24, 27100 PAVIA, ITALIA
Tel/Fax +39-0382-525234 Laboratori
Tel/Fax +39-0382-526208 Segreteria
Web http://www.unipv.it/cibra
________________________________________________________________________
________________________________________________________________________
|