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Re: fostex fr-2le high frequency noise

Subject: Re: fostex fr-2le high frequency noise
From: "umashankar" umashanks
Date: Thu Jun 5, 2008 7:18 pm ((PDT))
it is one of the things that does turn me off phantom power from digital (o=
r even newer analog) equipment. most of their circuits run on five volts, a=
nd the phantom voltage is generated either by an ic designed for it, or wit=
h some kind of an oscillator. things work some of the time, but there will =
always be a mic which will push the oscilator frequency or its harmonics do=
wn to where you can here it. i generally try and run the phantom supply fro=
m a string of nine volt batteries, still the quietest way of going about it=
. and many mics actually are quite happy with anything over 12 volts so it =
is worth checking out to see how many batteries ou have to string.
umashankar

=A0i have published my poems. you can read (or buy) at http://stores.lulu.c=
om/umashankar



----- Original Message ----
From: Carter Scholz <>
To: 
Sent: Friday, June 6, 2008 6:44:09 AM
Subject: [Nature Recordists] fostex fr-2le high frequency noise

Hi,

I recently bought a Fostex FR-2LE and I've been making some test=A0
recordings with it.=A0 I've noticed a steady tone that shows up only=A0
when phantom power is turned on.=A0 When sampling at 96/24, the tone is=A0=

on both channels at about 30,700 Hz; with trim and gain up full,=A0
using AT 3032s, it is about -66 dB (L channel) and -72dB (R=A0
channel).=A0 If the internal mics are used, with phantom on, the tone=A0
is there, but at a lower level.=A0 When sampling at 44/16, the tone is=A0
somewhere around 16 kHz, about the same levels.=A0 If phantom is turned=A0=

off, and internal mics used, there is no such noise at any sample rate.

I assume this is electrical noise from the switching circuit used to=A0
generate the P48.=A0 Has anyone else observed it?=A0 Is this typical of=A0=

the Fostex, or do I have a bad unit?=A0 And why would it change=A0
frequency depending on the sample rate?

It's a small amount of noise, but if you shift the 96/24 file down=A0
three octaves, it is definitely audible.

Carter Scholz


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