Re: Disk noise in audio

Doug Laidlaw wrote:

I am running a Gigabyte motherboard with Mandriva 2008.1 and KDE. Using
the onboard AC97 for sound. and external powered speakers.

Sounds are audible in the speakers at low level which sound almost like
instability, but which vary with hard disk activity.

Can you redefine "which sound like instability"?

Muting the sound with Kmix stops the noise.

Just a wild guess, not from an IT perspective but from my experience as a
musician... It is possible that either your speakers or - more likely -
your soundchip is experiencing microphonics. Concretely, this would boil
down to your soundchip picking up the vibrations from your hard disk
activity and amplifying them.

I myself am mainly an electric guitarist. Real electric guitars make use of
electromagnetic induction pickups - basically composed of one or two
bobbins with coil wire, with a magnet inside the bobbin - and can therefore
only be used with magnetically conductive strings, which pass through the
top of the pickup's magnetic field - we call this the magnetic window.

You pluck the string, it starts vibrating in the magnetic field and thus
disrupts the field, and this causes a signal to be generated in the coil
wire of the bobbins. As such, electric guitar pickups are not microphones,
because they can (in theory) only pick up the vibration of a magnetically
susceptible alloy string in their magnetic window.

However, on older electric guitars, poorly shielded and loosely assembled
pickups tend to be microphonic and pick up other sounds as well, such as
tapping on the guitar's wood or pickguard - this is especially true when
the pickups are mounted to the pickguard (like on a Fender Stratocaster)
instead of directly into the wood (with our without a metal or plastic
mounting ring) as more common with e.g. Gibson, Ibanez, Jackson, et al.

The microphonic effect is caused by the same principle through which
piezo-electric pickups on electric-acoustic guitars work and can be
eliminated by assembling the pickups more firmly, potting them in wax
and/or mounting them to the guitar body directly instead of to the
scratchplate.

My guess is that your soundcard is acting like a piezo-electric pickup,
which may not be the fault of the chip itself, but rather of the
motherboard design.

There are also other factors that could create disturbing sounds, such as
the EM interference from a rheostat. This is why Gibson invented the
humbucking pickup in the mid 1950s. Basically and simplified, a humbucker
pickup consists of two coils, mounted above a single magnet but on opposite
magnetic poles. These poles are extended to run through the center of the
bobbins via (usually iron) polepieces to extend the magnetic field so that
the strings pass through it.

Both coils are connected in series and 180° out of phase with one another.
The phase reversal and series connection then eliminates the humming, but
it would normally also eliminate the actual guitar sound, if it wasn't for
the fact that having both coils on opposite sides of the magnet's polarity
also generates a 180° phase reversal, which brings the actual electric
guitar sound of each coil back in phase with eachother. Humbucking pickups
do sound "fatter" than single coil pickups because of the series connection
- a sound that's quite beautiful and warm in its own right, though - but at
least the hum is canceled.

Can I block these sounds with suppressors, or similar? I don't have any
ferrite suppressors handy at the moment.

I think it would be best to make sure your hard disk's vibrations are muted
sufficiently. There are several mounting brackets and kits available to
this end, but I have no experience with them myself, and one must of course
also keep their possible negative effect on heat dissipation into
account... :-/

As for the motherboard... There's little you can do about that.
Motherboards are manufactured to form factor standards which also designate
the holes for the screws by which you attach the motherboard to the
chassis, and so my guess is that your motherboard has its sound chip
located in a less fortunate place where the board is susceptible to
mechanical vibrations inside the chassis. :-/

Anyway, just my two cents again... :-/

--
*Aragorn*
(registered GNU/Linux user #223157)
.

Relevant Pages

  • Re: 2 into 1 will it work.
    ... are built into the pickups or are separate doesn't matter, ... benefits of using active electronics in the first place. ... Active Pickups - Generally chosen when you want a sound uncolored by the ... replacing batteries in my instruments, I want cut and boost tone controls, ...
    (alt.guitar.bass)
  • Re: EQ for acoustic guitar
    ... As a bonus it also has the XL4 mic preamps which are also very powerful ... The sound is a little "discrete", ... musically with guitar as I'd like, ... acoustic guitar pickups need. ...
    (rec.audio.pro)
  • Re: Pickup wiring - can it go wrong and not know?
    ... If the pickups are out of phase it will sound nasally ... it can be a good sound and is a distinct variation in tone options. ... I bought a beginner-grade Yamaha bass so I can lay down ... The bridge pickup blend(?) also works fine doesn't sound like phase ...
    (alt.guitar)
  • Re: Bright humbucker
    ... It doesn't have to be a humbucker. ... >> complex clean sound with no bass boom and plenty of high ... >Tele you'll have to buy a Tele ... ... >pickups that fit into a standard humbucker cavity. ...
    (alt.guitar)
  • Re: M160
    ... that they're great for strings, winds, and electric guitars. ... I had one for years and couldn't get it to sound good on anything. ... I play fiddle myself, and found a Blue baby bottle has a great sound ... horn sectionin stereo. ...
    (rec.audio.pro)