BT878 capture audio problem - humming

[jp1234]

[System specs at bottom]

Hi,

I installed my first TV tuner card (AverTV PCI stereo)in my system last
week. After capturing some shows, I've noticed that there is a hum in the
captured audio.

After trying to isolate the source I found out that it's the tuner card
where it starts. The tuner outputs audio to the soundcard through a
stereo cable. I removed the jack from the tuner's output (which goes to
the sound card line-in) and plugged in a pair of earphones to see if the
hum was generated in the tuner card and indeed it was.

Then I also disconnected the TV cable going to the tuner. The hum was
still there.

The strange thing is it's not a constant hum, but it varies with the
mouse movement, pressed keys, and hard disk usage (yes, the hard disk
usage pattern is amplified through the subwoofer, as if the drive itself
wasn't loud enough).

The problem is not so evident during viewing TV. But with captured shows,
I usually have to normalize the audio, and this makes the hum pretty
obvious. Also, while watching TV on my PC, the hard disk is usually not
doing much.

For example, while capturing with AVI_IO, the hard drive is in continuous
use. And the hum pattern follows the hard drive usage intensity. Of
course, I coudn't remove the hum in Cool Edit since the pattern of the
hum keeps varying

There is also a constant high pitch noise in the sound captured, but I can get rid of that by setting a couple of notch filters (narrow band) at 15683Hz and 15680Hz.

I don't even have the slightest idea where to start. The simplest thing
would be to return the card, but there is no guarantee that the next one
I buy will perform OK. I would rather solve this problem. More than
likely the problem is at my end, but I don't know what it is!

*Any* help or at least pointers will be very much appreciated! Thanks.
______________________
System specs

Pentium III 500, 7200 RPM 30 GB Seagate Barracuda, 384 MB SDRAM.

Fresh install of Windows XP with all updates/patches.

Capture driver BTWinCap, TBS Montego II soundcard, Speakers H/K 595.

[BKL]

I experienced a similar problem with my I/OMagic PC PVR. The noise stopped when I changed the settings to capture DV from my Dazzle DV Bridge instead of the tuner card. The DV Bridge turns analog input into DV and I can then use the CyberLink PVR software to capture straight into MPEG-2. I just started experimenting with this last night, but the capture quality seems as good as or better than what I was getting from ULead VideoStudio version 6. The hum is definitely gone! Still don't know the real cause of the humming noise, though!

[greddyrps13]

I have the same problem...so i'm bumping this topic.

[Aztec_gizmo]

I have the same problem too.

[FOO]

The nice metal sheilding on the tuners is only
effective for electric fields and is about
useless for magnetic fields. A PC power
supply has to be as cheap as possible and so
has minimal magnetic shielding. The disk drive
has a petty hefty spindle motor and the head positioner
is powerful too. The drive chassis are aluminum
which is no good for magnetics.

The Audio amplifiers are probably outside the shield anyway

I used to do Electromagnetic Shielding for a living and
I can't believe EVERONE is not having problems. A Pc
chassis is a mess. I can only recommend moving the
tuner card as far away from the power supply as possible
and maybe try putting a flat IRON or STEEL plate next to the
capture card.

EMI is not a science, it's Voodoo

[FOO]

I just realized that you had noise at 15 KHz. That's a famous
problem with TVs. Its the horizontal sweep frequency.
Nothing to do about that