whats that noise?

Hi All

Question for the techies -

I am sure that this one of those questions where you roll your eyes, tut
under your breath and sigh because the answer is so bloody obvious to
anyone who knows what they are doing, but here goes anyway........

I have a professionally installed mast head amp with 4 outputs. One
goes down to the living room and appears to work just fine. I installed
another line down to a bedroom and that seems to be ok. However, i have
just installed line 3 down to my office - another bedroom. I fitted an
F Plug to one end and screwed it into the amp/splitter, ran the cable
along the loft floor and down through a hole in the ceiling and into the
back of a Grundig GUDB20USB3 (records to USB flash drives or hard drives
via 3 usb slots on the front) freeview box - i fitted a cheap and
cheerful aerial plug to the end of the coax. Grundig plugs into an LG
combined monitor and TV via a scart lead. I am fairly confident that
the cable has not been crushed or kinked etc. Its not easy to get back
into the loft to check it but could be done if needs be.

The picture seems fair enough but something is not right with the sound.
I am getting a cross between a buzz and a hum! It is especially
noticeable at low volume and the noise changes as the scenes change in
the tv broadcast! ie fi you go from tv programme to advert the
buzzy/hum will change tone and volume and each time the picture jumps
from one cut to another the tone of the buzzy hum changes.

Its just possible that the coax is laying a bit too close to some twin
and earth, but surely that would mess the picture up as well? How close
can twin and earth and coax lay beside each other before there is a problem?

I'll buy a decent aerial plug and remake the end of the cable, I am
pretty confident that the F Plug is fine - what could go wrong with
fitting an F Plug? The coax is the same stuff as used for all the other
cable runs and was purchased as being suitable for a digital
installation (is it CT100??) and came from a reputable aerial supplies
company in Cambridge.

The Grundig worked just fine whe i used it elsewhere.

Is there a meter of some kind that the aerial lead can be plugged into
and check the signal quality not just its strength?

Any suggestions and solutions appreciated as the noise when combined
with my tinitus is driving me to distraction and until I get rid of the
noise I can't record anything off of Freeview (







regards



Dudley


REMOVE THE OBVIOUS TO REPLY!

In article ,
Dudley Simons wrote:
Hi All

Question for the techies -

I am sure that this one of those questions where you roll your eyes, tut
under your breath and sigh because the answer is so bloody obvious to
anyone who knows what they are doing, but here goes anyway........

I have a professionally installed mast head amp with 4 outputs. One
goes down to the living room and appears to work just fine. I installed
another line down to a bedroom and that seems to be ok. However, i have
just installed line 3 down to my office - another bedroom. I fitted an
F Plug to one end and screwed it into the amp/splitter, ran the cable
along the loft floor and down through a hole in the ceiling and into the
back of a Grundig GUDB20USB3 (records to USB flash drives or hard drives
via 3 usb slots on the front) freeview box - i fitted a cheap and
cheerful aerial plug to the end of the coax. Grundig plugs into an LG
combined monitor and TV via a scart lead. I am fairly confident that
the cable has not been crushed or kinked etc. Its not easy to get back
into the loft to check it but could be done if needs be.

The picture seems fair enough but something is not right with the sound.
I am getting a cross between a buzz and a hum! It is especially
noticeable at low volume and the noise changes as the scenes change in
the tv broadcast! ie fi you go from tv programme to advert the
buzzy/hum will change tone and volume and each time the picture jumps
from one cut to another the tone of the buzzy hum changes.

Its just possible that the coax is laying a bit too close to some twin
and earth, but surely that would mess the picture up as well? How close
can twin and earth and coax lay beside each other before there is a
problem?

I'll buy a decent aerial plug and remake the end of the cable, I am
pretty confident that the F Plug is fine - what could go wrong with
fitting an F Plug? The coax is the same stuff as used for all the other
cable runs and was purchased as being suitable for a digital
installation (is it CT100??) and came from a reputable aerial supplies
company in Cambridge.

The Grundig worked just fine whe i used it elsewhere.

Is there a meter of some kind that the aerial lead can be plugged into
and check the signal quality not just its strength?

Any suggestions and solutions appreciated as the noise when combined
with my tinitus is driving me to distraction and until I get rid of the
noise I can't record anything off of Freeview (


since the receiver is a digital one, it would seem most likely that any
audio distortion/noise is created by the receiver itself. Have you tried
it in another room?

--
From KT24

Using a RISC OS computer running v5.16

On Tuesday, May 17th, 2011 at 16:36:58h +0100, Charles explained:

since the receiver is a digital one, it would seem most likely that any
audio distortion/noise is created by the receiver itself.

Ineeed so, or a problem in the audio link from the digital converter box to the
television receiver.

Several tests could be done to ascertain the source of the problem

1) The simplest first test -- try a different and preferably better
quality SCART cable to connect the digital converter box to the
television receiver and check to see if the audio distortion is
still present.

2) If the digital converter box has audio LINE out (usually via RCA jacks,
sometimes 3,5 mm stereo jack) then connect these to an amplifier and
loudspeakers or combined amplified loudspeakers and listen to hear if
the noise distortion is present from that source.

3) If the digital converter box has digital audio out (either coaxial SPDIF
or optical) connect this to a digital audio decoder or PC sound card
and listen on headphones or loudspeakers connected to the digital audio
decoder or PC to hear if the noise distortion is present from that source.

If test 1 makes no difference and tests 2 and 3 reveal no distortion,
then the distortion is being created in the television receiver itself.

If test 2 alone results in distortion, then there is something bad happening
with the coversion of the MPEG-2 digital audio to analog in the digital
converter box.

If test 3 reveals audio distortion, then it indicates that the box should
be returned from whence it was purchased.

Dudley Simons wrote:

I have a professionally installed mast head amp with 4 outputs. One
goes down to the living room and appears to work just fine. I installed
another line down to a bedroom and that seems to be ok. However, i have
just installed line 3 down to my office - another bedroom. I fitted an
F Plug to one end and screwed it into the amp/splitter, ran the cable
along the loft floor and down through a hole in the ceiling and into the
back of a Grundig GUDB20USB3 (records to USB flash drives or hard drives
via 3 usb slots on the front) freeview box - i fitted a cheap and
cheerful aerial plug to the end of the coax. Grundig plugs into an LG
combined monitor and TV via a scart lead. I am fairly confident that
the cable has not been crushed or kinked etc. Its not easy to get back
into the loft to check it but could be done if needs be.

The picture seems fair enough but something is not right with the sound.
I am getting a cross between a buzz and a hum! It is especially
noticeable at low volume and the noise changes as the scenes change in
the tv broadcast! ie fi you go from tv programme to advert the
buzzy/hum will change tone and volume and each time the picture jumps
from one cut to another the tone of the buzzy hum changes.

This sounds like a mains earth-loop problem to me, caused by the fact
that the Grundig is (probably) earthed through the aerial cable and the
mast-head amp, and also through the scart lead via the TV/monitor to the
computer. What happens if you disconnect the computer from the monitor?

"Dudley Simons" wrote in message ...
Hi All

Question for the techies -

I am sure that this one of those questions where you roll your eyes, tut under your breath and sigh because the answer is so
bloody obvious to anyone who knows what they are doing, but here goes anyway........

I have a professionally installed mast head amp with 4 outputs. One goes down to the living room and appears to work just fine.
I installed another line down to a bedroom and that seems to be ok. However, i have just installed line 3 down to my office -
another bedroom. I fitted an F Plug to one end and screwed it into the amp/splitter, ran the cable along the loft floor and down
through a hole in the ceiling and into the back of a Grundig GUDB20USB3 (records to USB flash drives or hard drives via 3 usb
slots on the front) freeview box - i fitted a cheap and cheerful aerial plug to the end of the coax. Grundig plugs into an LG
combined monitor and TV via a scart lead. I am fairly confident that the cable has not been crushed or kinked etc. Its not easy
to get back into the loft to check it but could be done if needs be.

The picture seems fair enough but something is not right with the sound. I am getting a cross between a buzz and a hum! It is
especially noticeable at low volume and the noise changes as the scenes change in the tv broadcast! ie fi you go from tv
programme to advert the buzzy/hum will change tone and volume and each time the picture jumps from one cut to another the tone of
the buzzy hum changes.

Its just possible that the coax is laying a bit too close to some twin and earth, but surely that would mess the picture up as
well? How close can twin and earth and coax lay beside each other before there is a problem?

I'll buy a decent aerial plug and remake the end of the cable, I am pretty confident that the F Plug is fine - what could go wrong
with fitting an F Plug? The coax is the same stuff as used for all the other cable runs and was purchased as being suitable for a
digital installation (is it CT100??) and came from a reputable aerial supplies company in Cambridge.

The Grundig worked just fine whe i used it elsewhere.

Is there a meter of some kind that the aerial lead can be plugged into and check the signal quality not just its strength?

Any suggestions and solutions appreciated as the noise when combined with my tinitus is driving me to distraction and until I get
rid of the noise I can't record anything off of Freeview (







regards



Dudley


REMOVE THE OBVIOUS TO REPLY!

I'd be looking at the SCART link between the receiver and the screen, not
the aerial cable.
Is it a very thin "pound shop" type? All the signal wires in these are unscreened,
there is just a bit of an overall braid, and they crosstalk like buggery.

Don't spend more than a fiver on a replacement!


--
Graham.

%Profound_observation%

I'd also suggest when these tests are done that the scart is unplugged and
then plugged in while listening.
It sounds to me that analogue video signals are getting into the sound at
analogue stage.
Its almost like when we all used modulators and analogue connections and
the video was over the top, some tvs sound buzzed loudly according to
picture content.

Brian

--
Brian Gaff -
Note:- In order to reduce spam, any email without 'Brian Gaff'
in the display name may be lost.
Blind user, so no pictures please!
"J G Miller" wrote in message
...
On Tuesday, May 17th, 2011 at 16:36:58h +0100, Charles explained:

since the receiver is a digital one, it would seem most likely that any
audio distortion/noise is created by the receiver itself.

Ineeed so, or a problem in the audio link from the digital converter box
to the
television receiver.

Several tests could be done to ascertain the source of the problem

1) The simplest first test -- try a different and preferably better
quality SCART cable to connect the digital converter box to the
television receiver and check to see if the audio distortion is
still present.

2) If the digital converter box has audio LINE out (usually via RCA jacks,
sometimes 3,5 mm stereo jack) then connect these to an amplifier and
loudspeakers or combined amplified loudspeakers and listen to hear if
the noise distortion is present from that source.

3) If the digital converter box has digital audio out (either coaxial
SPDIF
or optical) connect this to a digital audio decoder or PC sound card
and listen on headphones or loudspeakers connected to the digital audio
decoder or PC to hear if the noise distortion is present from that
source.

If test 1 makes no difference and tests 2 and 3 reveal no distortion,
then the distortion is being created in the television receiver itself.

If test 2 alone results in distortion, then there is something bad
happening
with the coversion of the MPEG-2 digital audio to analog in the digital
converter box.

If test 3 reveals audio distortion, then it indicates that the box should
be returned from whence it was purchased.

On 17/05/2011 15:44, Dudley Simons wrote:
Hi All

Question for the techies -


thanks for all the replies. I will have a poke around at the weekend
and see what i can sort out.

First thing to do will be to pull the fuseon the lighting circuit and
make sure there is no interference from the mains cables as that will
save hours of lugging stuff around in the loft

Most of the other tests look pretty straight forward.

The scart lead is the one that came with the Grundig so it ought to be
of at least passable quality, but how do you tell if a cable is any good?

I have another identical Grundig Freeview box down in the living room so
I can swop them over and see if the other box does the buzzy/hummy thing
as well and if the currently buzzy/hummy box continues to buzz and hum
when plugged in downstairs.

I'll post the results next week and let you know how I get on.



many thanks



Dudley




remove THE OBVIOUS to reply

On Wed, 18 May 2011 07:36:42 +0100, "Brian Gaff"
wrote:

I'd also suggest when these tests are done that the scart is unplugged and
then plugged in while listening.
It sounds to me that analogue video signals are getting into the sound at
analogue stage.
Its almost like when we all used modulators and analogue connections and
the video was over the top, some tvs sound buzzed loudly according to
picture content.

Oh yes I remember that, an ITT B&W I think. The audio buzz depended on
the contrast of the pictures. Text or subtitles were worst. None of my
other TVs were affected. Also an early computer's sound card used to
pick up hissle and shash from some of the other components.

The Grundig worked just fine whe i used it elsewhere.

Oh dear, my suggestion would have been to try the same kit on other
aerial outputs.

Maybe the signal level on the one cable is reduced or compromised and
interracts with the box's internals in a non-optimal way resulting in
vision signal getting into the sound circuitry somehow.

In message , Albert Ross
writes
On Wed, 18 May 2011 07:36:42 +0100, "Brian Gaff"
wrote:

I'd also suggest when these tests are done that the scart is unplugged and
then plugged in while listening.
It sounds to me that analogue video signals are getting into the sound at
analogue stage.
Its almost like when we all used modulators and analogue connections and
the video was over the top, some tvs sound buzzed loudly according to
picture content.

Oh yes I remember that, an ITT B&W I think. The audio buzz depended on
the contrast of the pictures. Text or subtitles were worst. None of my
other TVs were affected. Also an early computer's sound card used to
pick up hissle and shash from some of the other components.

The Grundig worked just fine whe i used it elsewhere.

Oh dear, my suggestion would have been to try the same kit on other
aerial outputs.

Maybe the signal level on the one cable is reduced or compromised and
interracts with the box's internals in a non-optimal way resulting in
vision signal getting into the sound circuitry somehow.

I seem to remember that the usual reason for a buzz like that was
that the channel was slightly out of tune.
--
Ian

In article ,
Ian wrote:

[Snip]

I seem to remember that the usual reason for a buzz like that was
that the channel was slightly out of tune.

that was certainly one reason.

--
From KT24

Using a RISC OS computer running v5.16