Working CD-4 (software) Demodulator!

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kfbkfb

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Louis Dorren claimed that a true Shibata stylus would bridge the groove damage (in the lower half of the record groove) and pick up the baseband and carriers from the upper half of the groove, thereby providing the CD-4 decoder with a good quality signal.

I don't recall reading about anyone testing decoding of a worn CD-4 disc with both a true Shibata stylus and a line contact stylus (provided other CD-4 requirements are met) to see if the true Shibata stylus saves the day.

(attachment-it looks like a Shibata stylus would work whereas other line contact stylus shapes may not)


Kirk Bayne

Shibata.jpg
 

Doug G.

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Of course, success of bridging worn sections of the groove would depend on exactly at what level, in the groove, the worn area is and the positioning and length of the vertical contact area of the Shibata or other line contact stylus.

Even though I personally believe the genuine Shibata is superior for CD-4, my other cartridges with variations of line contact styli (Pickering XUV, Empire 4000, Audio Technica) work excellently, too.

Doug
 

kfbkfb

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It looks to me like even severe damage is restricted to the lower half of the record groove, so a stylus shape that contacts just a little of the upper half should provide a low distortion signal to the CD-4 decoder.


Kirk Bayne
 

MidiMagic

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What about dust or powder impacted into the groove that makes bumps?

The worst case of CD-4 damage I ever saw was caused by a woman putting on face powder at a mirror next to the turntable.
 

kfbkfb

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That is sort of breaking the rules, vinyl records need to be kept clean, another comment by Louis Dorren was that the record companies knew all types of records should be kept clean, but the marketing people thought it would be a negative to mention that, so it wasn't mentioned often (until CD-4).

The later CD-4 demods temporarily mute the carrier decoding output on carrier loss (both the QSI-5022 and the software decoder).


Kirk Bayne
 

Doug G.

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I treat my CD-4 records exactly like all my other ones, they are clean and they get dusted with a Discwasher brush before each play, and they are fine.

I expect that applying face powder right next to any record, at all, is a pretty rare occurrence.

Doug
 

MidiMagic

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I treat my CD-4 records exactly like all my other ones, they are clean and they get dusted with a Discwasher brush before each play, and they are fine.

I expect that applying face powder right next to any record, at all, is a pretty rare occurrence.

Doug
You are expecting clean conditions at all times. But in this case, damage has already occurred.

This happened in a record store. They had put mirrors all around the quad display, possibly to make the room seem bigger. I was sitting in the "best seat", a chair in the middle of the 4 speakers. This was when I first heard the cogging effect with CD-4. I had to turn my head to hear any side panning.

Then the woman put the powder on her face using the mirror next to the turntable. I immediately heard snapping sounds like people breaking pencils in half. The store manager came running and asked if I had done anything. I told him about the woman.

He tried to clean the record. There was a lot less static on the parts of the record that had not been played, but the parts that had already been played sounded just as bad as before.

Now, can this software remove this kind of noise?
 
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quattro64

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Lou Described how he came up with his special CD-4 record cleaner in of his papers. Yes, CD-4 records need to be clean. They also need to be played back with the correct stylus. Pushing dirt into the groves of these records might appear like permanent damage. Since it is likely his special formula is lost to us, It is probably best to find someone with a sonic record cleaner. Then keep them clean after that.
 
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