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    Grooves in close up
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These images were made with an Intel Play microscope at 200x magnification and the Mac OSX microscope software. The images were quite saturated, bringing out the minute colour difference between old an modern vinyl. Funny enough the old vinyl is browner, where as the new vinyl is more blueish. 

Note the square 'valleys' of an old mono EP and that the sides of the grooves of a modern 45 rpm single are in a 90 degree angle, which allows uncorrelated (stereo) soundswaves to be cut. In practice, this difference hardly exceeds 18 dB, or a 1:8 factor. If the curves are too different, the sides can get so close that the groove can actually dissapear. This is why LP masterers check for 180 antiphase sounds in recordings. (especially in low frequencies, as those waves tend to have higher amplitudes.)

The small details in the curves represent the high frequencies, the side to side whobble or movement of the curve ar bass frequencies. The white spots are dust and you can also see some fine scratches, probably caused by the sleeve. (You can't see the 90 degree angle to well here, as I lighted the single almost horizontally.)

Bass is recorded on a low volume on vinyl, high frequencies are boosted. This is then corrected in the phono preamp in the amplifier, according to the RIAA standard filtercurve. If vinyl records were recorded with a flat frequency response, the 'revolutions' are very likely to cross eachother.

I also made a little quicktime movie of a very modern (2002) pressing. You might have to look twice to understand you're looking at a v shaped groove. At certain places you can see some high frequencies that are in anti-phase. [quicktime movie 7MB]
 


 
 
 
 
 

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Alle teksten, tekeningen en geluiden op deze site zijn van de hand van D.D. Krooshof.
Alle rechten voorbehouden.    Vermeningvuldiging  en  verspreiding  mag  uitsluitend
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