Re: HD- Beat frequency on 2 drives ?

"Eric Gisin" wrote:
"Timothy Daniels" wrote: 
"Eric Gisin" (a.k.a. Rod Speed) wrote:
> "Timothy Daniels" wrote:
>> "George Pontis" wrote:
>> > The sum and idfference terms arise from _mixing_, which requires
>>> some non-linearity. Just adding the two sinewaves gives you two
>>> sinewaves.
>>
> Correct.
>>
>>     The sum of two sine waves gives the sum and the difference of the
>> two sine waves.  The difference is commonly known as the "beat frequency".
>> If the two frequencies are similar, the sum is usually limited in amplitude by
>> characteristics of the medium, but not by the math.  In AM radio, the sum
>> of a RF carrier wave and an audio wave (widely different in frequency
>> and assumed for simplicity to be sine waves) gives sine waves having
>> the sum and the difference of the two frequencies - known as sidebands.
>> No non-linearity is required.  See:
>> http://hep.physics.indiana.edu/~rickv/Beats.html
>> This all falls out of Fourier analysis, basic college sophomore physics/math.
>>
> You don't have a fucking clue. Adding two sine waves produces no others.
>
> Amplitude modulation is NOT adding two signals.
> It is multiplication of the carrier by a biased signal.

    <hee hee>  You're cute when you're offensive.
When you have time, read the web page.

You are a fucking moron, Timmy. Neither of you have a clue.

You cited a bird course in the physics of sound and music.
Come back when you have read some radio electronics.



   <hee hee>  "Radio & Electronics".  Wasn't that a magazine?
Or was that a correspondence course?  Seriously, though, folks,
Fourier analysis will show that any waveform can be reproduced
by a combination of sine and cosine waves of various frequencies
and phases (most times containing an infinite no. of components),
and that such a combination of sines and cosines are indistinguish-
able from the original waveform.  As a matter of fact, they are identical.
In the case of two sine waves, they are indistinguishable from a
combination of two sine waves that have frequencies that are the
sum and the difference of the two original sine waves' frequencies.
Just ask any undergraduate physics student.

    In the case of two hard drives spinning at slightly different
speeds (and who says that hard drives spec'd at 7200 rpm
must spin at exactly 7200 rpm?) there could easily be a beat
note that is audible.  The question is merely why the rotation
of the platters is coupled to the air - is there an inherent platter
imbalance built into the product that causes vibration in the drive
housings?  I'd guess that the vibration is from bad bearings in
both of the hard drives.

*TimDaniels*
.

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