wrote:
On Wednesday, December 19, 2018 at 11:27:25 PM UTC+1, Paul wrote:
wrote:
Hello,

In this HDMI cable noise test the following was done:

PC connected to power box.
Monitor connected to same power box.
Receiver connected to same power box.

Powerbox connected to wall socket (no earth grounding/wire)

PC - VGA cable - Monitor
PC - USB cable - Keyboard
PC - USB cable - Mouse
PC - HDMI cable - Receiver
Receiver - analog cables - Speakers

Everything else disconnected.

The test was recorded on video/audio and placed on youtube:

HDMI cable noise test video:

https://youtu.be/bZSdQcPWKkg

During this test a very clear NOISE signal can be heard coming from the HDMI cable when the PC is ON.

When the PC is OFF and/or disconnected there is no NOISE signal.

I think this video is very clear evidence that there is some kind of NOISE signal being transmitted across this HDMI cable.

Perhaps friday I may repeat this test with a high quality/expensive HDMI cable to see if it makes any difference. (If the other person agrees to provide this cable).

What is the source and why is there noise ?
Hum comes from analog ground loops.

Occasionally hum comes from a failure in
the power rectification and filtering section.
(In the past, many AV receivers did not regulate V+
and V- on the power amp section.)

Sometimes the ground loop is part of the
design of the AV, and there's nothing you can
do to fix it.

Sometimes, the AV is influenced by crappy house wiring.

And sometimes, leaving your analog 1/8" plugs connected
at the same time as you plug in an HDMI cable, causes
the problem. When testing HDMI, the *only* input cable
to the AV should be the HDMI cable, while you test for
noise. If there is still hum, it suggests the AV
receiver is not floating and has a hard reference
to ground.

And the ferrite lumps on the HDMI cable, do not filter
AC noise. The ferrite works at 10MHz-30MHz for example,
filtering RF from the computer. The ferrite does nothing
at 50Hz or 60Hz.

I have a hard enough time removing ground loops from
my own stuff here, so I'm not the best person to
advise on this.

Paul

Somebody (on another newsgroup) mentioned "pin 1 problem" googling this reveals some info about that.

Try googling "the pin 1 problem".

Let me know what you think of this pin 1 shielding/earthing (?) problem.

Bye,
Skybuck.

That's an analog interconnect concern.

The HDMI cable is pure digital.

There's a difference.

For HDMI, the high speed lanes are differential, and
the receiver subtracts D+ and D- to develop a data bit
from it. Any signals impinging common mode on both
D+ and D- at the same time, are rejected. And this
can happen, up to the common mode input limit of the
technology. You can still upset a technology like that,
but it takes more effort.

Ethernet is also differential. But Ethernet is *unshielded*
and what do you notice ? It works. It works reliably.
It uses transformers to reject common mode signals. If
you hang a scope off the floating wires, the noise
amplitude is *huge*, but the fake noise as it were,
is stopped in its tracks by the common mode rejection
of the transformer. It's one of the single nicest
inventions in electronics, as far as I'm concerned.

Your XLR microphone problem, the signal is analog and
a microphone may have lower amplitude signals involved.
There are a number of different microphone types, and
each has a characteristic voltage range. For example,
my one good microphone here, is an electret, followed
by a chip amp (not an opamp) inside the microphone. The
result is a line level (1 volt AC) signal is presented,
and that microphone properly belongs plugged into Line-In
instead of Microphone-In. I have other crappy microphones
without that here, and there's no comparison on quality.
You can actually hear sounds in the room with the Line
Level microphone. It's much more sensitive, and any
noise currents (S/N) are much smaller compared to the
signal.

An AV receiver can have a ton of stuff wired to
it, and it's possible some other wiring is compromising
your S/N ratio. Check whether you're running 7.1 analog
1/8" wiring *at the same time* as the HDMI cable.

Paul