Re: Noise when downloading files

On Mon, February 4, 2019 2:56 pm, jonetsu wrote:
> I forgot to mention networking.  It's directly connected by wire.  That
> network wire though is one I had left, it's a 25m long wire that's
> rolled up near the desk to pick up the extra length.

It would be tedious, you could probably move wires around to try to
determine if the noise is picked up by cabling to the amplifier or
speakers, or if the noise is picked up internally by the sound card or
audio interface you are using.  An  interface built onto the computer
motherboard could pick up noise directly from other components (power
supply noise, or high frequency noise modulated down at the line level
amplifier components), or noise picked up on the cables to the speakers. 
If the audio cable runs near or across the network cable you could start
by just increasing the separate between the network and audio cables.
To really determine the source, since the speakers have the amplifiers
built in, you would have to disconnect the speakers and connect a battery
powered headphone amplifier to the audio interface output with short
cables, see if the noise was present when downloading a file.  If it was,
then the noise is originating in the audio interface.  If not, then
probably the connection between the interface and the speaker amplifier is
picking up the noise. Could be the audio interface or the speaker
amplifier which has the problem, so you would have to check again with a
long cable from the interface to the headphone amplifier (with the cable
physically in the same place, such as next to or running across the
network cable if it was before), then with a long cable to the powered
speakers, but instead of connecting to the audio interface have a resistor
connecting across the cable to simulate the output impedance of the sound
interface, see if the speakers pick up the noise with just the cable but
not the audio interface connected.  A cable with no resistor terminating
the input end is  more likely to pick up interference, so that is not a
fair test of the speakers.

> OTOH, there are so many inaudible waves going on, even in a plain house.

The strength of the fields falls off quickly with distance, so often just
separating the audio cables a meter away from the interfering cables will
cause the noise to become inaudible.

-- 
Chris Caudle


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