7 Feb
2014
7 Feb
'14
2:04 p.m.
On Thu, Feb 06, 2014 at 11:56:00PM -0500, Rick Green wrote:
I had heard the story about phonograph needles jumping
out of the
track. It made sense to me. On a stereo phonograph record, in-phase
energy (L+R) is represented as side-to-side motion of the needle,
and out-of-phase energy(L-R) is up and down motion. It can also be
thought of as the left channel is recorded on one side of the
groove(at a 45deg angle), and the right channel on the other side.
It seemed plausible that a kick drum panned all the way to one side
or the other might send the needle into the adjacent groove.
It shouldn't unless the player has a problem.
The cantilever of which the needle is the end has an elastic
mount in the cartridge. Together with the mass of the arm
and cartridge this forms a spring + mass system, which has
a resonance frequency.
Above that frequency the arm will not follow the groove,
the needle moves relative to the cartridge, and this
produces the signal. Below the resonance frequency the
whole arm will start to follow the modulation of the groove.
On a well-designed system, the resonance frequency should
be below the audio range, but still high enough to enable
the arm to follow any warping of the disk.
If the resonance frequency is in the audio range, then
a strong groove modulation below or at that frequency can
make the needle jump out. But this means bad design, or
the wrong combination of arm and cartridge.
Ciao,
--
FA
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)