Steve, I thought of a ground loop as you did, but I never heard a high
pitched one, only a 60 cycle one, that is why I ruled it out. you gave him a
lot of good suggestions to try.
----- Original Message -----
From: "Steve Jacobson" <steve.jacob...@visi.com>
To: "PC Audio Discussion List" <pc-audio@pc-audio.org>
Sent: Wednesday, September 11, 2013 10:07 AM
Subject: Re: AC line filter question
John,
Here are a couple of thoughts on this, although Gary may have some better
ideas.
First, have you been able to establish whether you hear the high-pitched
sound when recordings are being monitored? I have seen
it happen where sounds like this are introduced particularly when playing
back a recording made at a lower sampling rate.
If you can hear the sound while monitoring the mixer through your
computer, then check each of your inputs by turning all of the
gains down to see if this problem is being introduced by a particular
input. Extraneous noise can easily be introduced by a
microphone input if nothing is plugged in but the gain is up for example.
If you find that a particular input is causing the
problem, then determine if it remains if you disconnect the cable to that
input. Knowing which device is causing the problem
might help us come up with ideas.
Make sure your mixer isn't sitting on top of or just underneath another
device such as a modem or router.
If you find that you still hear the pitch even with all inputs durned
down, the problem is harder to find. However, it is still
worth unplugging all cables to the mixer except the USB cable that
connects it to the computer to see if the sound disappears. If
it does not, you should look at options that affect the USB interface to
your computer. Even trying another USB input or another
USB cable is worth while. If disconnecting all cables even with the gain
turned down removes the problem, reconnect each cable
until you figure out which cable starts the problem. If a digital device
is connected to that cable, it is possible that the
analog output of the digital device doesn't have remaining digital signals
filtered out very well. Another possibility is that
you have what is called a ground loop. Ground loops most often cause AC
hum to be added, but they can cause digitial interference
as well. They result when a device has two separate ground paths going to
a computer. For example, if you had an audio player
connected to computer speakers that are also connected to your computer, a
ground path will exist from that device to your
speakers and then to your computer. If that device is also connected to
the mixer, a second ground path exists from the device,
through the mixer, and then to your computer through the USB cable. This
isn't an exact science, though, and it can depend some
on how various devices are designed, and whether your mixer accepts
digital inputs as well as analog inputs and on and on. But
you have to narrow down the cause before you can attack it.
Another thing to check is whether you have other devices that might emit
interference that is getting into your system. For
example, older computer monitors or televisions can emit interference. If
such a device is too close to your equipment, this can
get into your system and result in audible interference when it mixes with
other digital signals.
Good luck.
Best regards,
Steve Jacobson
On Tue, 10 Sep 2013 22:45:44 -0400, John Chilelli wrote:
Gary,
I'm using a new Allen -Heath Zed 10Fx mixing board with usb interface
and my cableing is brand new as well. My Win 7 I3, 8gb computer is also
brand new and I'm using Audacity 2.0.3. In a way I'm glad you don't
think that it is line noise interference. But how do I go about
finding the problem? Oh I forgot to mention that I'm using one of two
new EV voice quality mics and a Kurzwell K2600. Any suggestions on how
I go about finding where the problem may be is appreciated.
Thanks,
John
On 9/10/2013 10:14 PM, Gary Schindler wrote:
That doesn't sound like an AC line problem. If you had an AC line
problem you would hear a 60 or 120 HZ hum. it wouldn't be high pitched.
It may be noisy circuitry in your mixer, coupled with a cabling
problem, such as poor shielding or an impedance mismatch.
----- Original Message ----- From: "John Chilelli" <j...@neo.rr.com>
To: "PC Audio Discussion List" <pc-audio@pc-audio.org>
Sent: Tuesday, September 10, 2013 5:48 PM
Subject: AC line filter question
Hi all,
I am experiencing some sort of high pitch line noise in my
recordings. I am using an Allen - Heath mixing board with a usb
interface into my Windows 7 computer using Audacity 2.0.4. I was
told that I should look into an AC line adapter, but I'm afraid that
the entire electrical system for tha room I am using is on one
circut, including overhead lights and fans. I wish to be able to get
rid of this line noise that exists even with the overhead fan off.
Can anyone make a good suggestion as to what I should do for this
problem?
Thanks,
John
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