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Ceramic Cartridges and RIAA Equalization, Plus: Sneak preview of Knowzy samples page
Knowzy
post Apr 26 2009, 20:32
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The upcoming page* showcasing the USB turntables samples I've been posting put a renewed focus on ceramic cartridges. This caused me to update the case against ceramic carts in the turntable guide.

I added a new section on RIAA equalization and would appreciate a review for technically accuracy. In particular, I would like you to pick apart this declaration:

QUOTE (USB Turntable Guide)
Ceramic cartridges don't require a pre-amplifier yet still approximate the RIAA curve. You might say that ceramic cartridges equalize the audio signal organically: They rely on their chemical composition to implement the RIAA curve.


Am I over simplifying? Are there capacitors or other components down the line that also affect the equalization of the signal or is it truly all in the cart itself?

As always, I appreciate your insights.

-Jeff

* Sneak preview. This is the only link on the Internet leading to that page.
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Knowzy
post May 1 2009, 06:06
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QUOTE (Arnold B. Krueger @ Apr 30 2009, 13:38) *
Actually Clive and I agree. The ceramic cartridge inherently rolls of the treble with a -6 dB/octave roll-off because it responds to the amplitude of the music in the groove, not the velocity.

I'm still pretty fuzzy on the difference between constant-amplitude and constant-velocity (I even went as far as asking the EE forum on PhysicsForum.com to define and contrast the terms- no takers yet).

My fuzziness aside, does this mean my declaration stands up, particularly if we replace my uber-Californian adverb "organically" with "mechanically?"
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Arnold B. Kruege...
post May 1 2009, 11:57
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QUOTE (Knowzy @ May 1 2009, 01:06) *
QUOTE (Arnold B. Krueger @ Apr 30 2009, 13:38) *
Actually Clive and I agree. The ceramic cartridge inherently rolls of the treble with a -6 dB/octave roll-off because it responds to the amplitude of the music in the groove, not the velocity.

I'm still pretty fuzzy on the difference between constant-amplitude and constant-velocity (I even went as far as asking the EE forum on PhysicsForum.com to define and contrast the terms- no takers yet).


Think about a sine wave plotted out the usual way. Think of the dot that plots the sine wave. As time progresses, the dot can be thought of as progressing across the page from left to right. The distance of the dot from the left of the plot is time, or if you will, the amplitude of the time.

The amplitude of signal represented by the dot can be thought of a number of ways, but by convention, we usually think of the amplitude of the dot as being the vertical distance from the hoizontal center line of the plot to wherever the dot is. Positive amplitude when the dot is above the center line, negative amplitude when the dot is below the center line.

As it goes across the page the dot has two velocities. One is the horizontal speed of the dot or its velocity in the time dimension from left to right, which we usually think of as being constant for the entire plot.

However, the dot also has a velocity going up and down the page which varies quite a bit. On the sloped parts of the wave the dot's vertical velocity is greatest, and on the flats on the top and bottom of the sine wave, the dot's vertical velocity is actually zero.

If the sine wave we plot represented the wiggles in a LP groove, a ceramic cartridge responds to the height of the dot, and a magnetic cartridge responds to the vertical speed of the dot.

Now, lets think about the plot of a sine wave whose amplitude remains the same but the frequency is rising as the dot goes across the page.

The waves are going to get more scrunched together on the right side of the plot, compared to the left side of the plot. Because the waves are scrunched on the right side of the plot, the sloped portions are going to be steeper. IOW, the vertical velocity of the dot will peak out at higher and higher velocites as the frequency rises.

So, if frequency is rising, and amplitude remains the same, then the (vertical) velocity increases. OTOH, if you wish to keep the vertical velocity the same, then you have do cut the amplitude as the dot goes across the page.

A constant amplitude wave would be a sine wave with the same height as the frequency rises. A constant velocity wave would be one whose amplitude shrinks as the frequency increases.

QUOTE
My fuzziness aside, does this mean my declaration stands up, particularly if we replace my uber-Californian adverb "organically" with "mechanically?"


Hmm, you said: "You might say that ceramic cartridges equalize the audio signal organically: They rely on their chemical composition to implement the RIAA curve."

I would reword that to say:

"You might say that ceramic cartridges equalize the audio signal mechanically: They rely on the way they convert the groove into a signal to implement an approximation of the RIAA curve."


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