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Practicality of reversing frequency response curve of phono cartridge / stylus

Burning question regarding phono cartridges and wondering how much this has been explored: 

How practical would it be to measure a phono cartridge's frequency response with a test record and then correct it with a digital signal processor to be ruler-flat, much like Genelec's GLM system does with a room? Does anyone offer a product that would do this? It seems that rather than spend thousands on a fancy cartridge, one could get by with an average cartridge and correct it with some rather simple processing (?)

My future plans are to use a CEDAR Cambridge processing system to archive the best examples I can find of early jazz music, and I'm forced by the nature of the records and the cartridges available to use a Shure V-15 VX with aftermarket 78-specific stylii, so I'm thinking it might be possible to correct for some of the imperfections of the cartridge if I have a baseline.

 

mke246
andysf's avatar
andysf
269 posts
 

CEDAR is a pretty old technology. I remember asking people who worked with it if it was really that good. No one thought that it was and it cost about $8000 back then.  That was 25 years ago!  I would try and find a SweetVinyl unit with SVNR.  There are lots of better mono cartridges for 78 rpm than Shure these days IMO though it is nice to have the flexibility with stylus size sometimes.

mke246 OP
36 posts
 

Thanks, good food for thought. A lot of what CEDAR does is pretty old, but there are still some things that have yet to be matched by other products, e.g. phase correction of mono groove walls, fixing lathe errors for 100 year old recordings, some more sophisticated EQ correction, and even some of the 78-specific crackle reduction. At a glance, SweetVinyl seems good for vinyl, but shellac is a whole different animal. In my experience, any vinyl product designed without shellac in mind will either absolutely murder shellac or be totally useless.

 

I agree that correcting for cartridge is probably small potatoes and almost not worth considering when dealing with shellac, but I'm still curious to hear the differences. Part of the reason is also wanting to have a library of ruler-flat transfers and not someday regretting that I could have done them better. 

The Shure V15Vx is about as good as it gets for 78s. Must-haves for any cartridge include swappable stylii and cantilevers that can take at least 5 grams of tracking force. You need at minimum 6 different stylii to be able to get best results. Groove widths vary widely. 

atmasphere's avatar
atmasphere
12,103 posts
 

Having said all that good phono cartridges are relatively flat.

Actually any magnetic or moving coil cartridge is known as a constant velocity device, which is to say that their output doubles with doubling the speed at which the stylus vibrates. So they have a rising 6dB/octave response. However you are correct in the response is a pretty straight line alone that 6dB/octave rise.

The RIAA curve is meant to compensate that as well as reduce high frequency noise on the LP surface. The RIAA curve has a step in it, which causes the actual equalization to be a bit of a wavy curve. This might be a bit tricky to set up in DSP.

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