1/2 Speed CD-4 (recording) ?

[kfbkfb]

Anyone tried this (it seems like the challenge would be to find a turntable that operates at 16.67rpm)?

One advantage of 1/2 speed CD-4 disc playback is that phono cart channel separation is generally good from ~7.5kHz to ~22.5kHz (and phono cart frequency response wouldn't a problem either).


Kirk Bayne

 

[winopener]

Think the problematic issue is the rumble noise; finding out a 16rmp deck isn't hard, but when you double the sampling the rumble doubles its frequency too.

 

[quadsearcher]

Seems like it would lose bass. If there's sound down at say 30hz, at half speed the cartridge would have to reproduce 15hz.
I've done it with 78s, paper-backed home recordings that would only track at 45, but there's not much low end there.

 

[par4ken]

I don't think that this would be a good idea.

If you were to build the turntable speed control that I mentioned in my Vinyl Journey thread you would have no problem getting the lower speed assuming your turntable has a synchronous motor. Rumble shouldn't be a problem with a good belt drive turntable. Rumble could be a problem with cheap turntables.

But why attempt it in the first place? To be able to use a regular stereo cartridge? I would think that there is sufficient separation at those high frequencies with a good CD4 cartridge. The two carriers should not interfere with each other unless the are close in level.

 

[kfbkfb]

But why attempt it in the first place? To be able to use a regular stereo cartridge?

It's a workaround to try to deal with the lack of new phono carts that work well for CD-4, probably all that would be needed would be a stereo cart w/good channel separation > 7.5kHz & Shibata stylus.

1/2 speed play of CD-4 disc --> stereo cart --> [software?] convert to full speed [I think the currently available software CD-4 demod will accept 1/2 speed input].

Then no worries about getting special low capacitance tone arm wiring, a cart that works for CD-4 [even on the inner grooves] and keeping 40+ year old consumer grade CD-4 demods working.


Kirk Bayne

 

[Owen Smith]

The currently available software CD-4 demod doesn't demodulate anything. As I understand it the approach is to decode CD-4 as if it is matrix encoded. I don't see how that achieves anything more that running CD-4 through a QS decoder ie it is synthesised quad.

 

[jupp369]

It's a workaround to try to deal with the lack of new phono carts that work well for CD-4, probably all that would be needed would be a stereo cart w/good channel separation > 7.5kHz & Shibata stylus.

1/2 speed play of CD-4 disc --> stereo cart --> [software?] convert to full speed [I think the currently available software CD-4 demod will accept 1/2 speed input].

Then no worries about getting special low capacitance tone arm wiring, a cart that works for CD-4 [even on the inner grooves] and keeping 40+ year old consumer grade CD-4 demods working.


Kirk Bayne

would it not be easier to invest once in a CD-4 cartridge than humble around with so many variables?
I use a Nagaoka JT 322 CD4 cartridge, you may get it for 150,- till 300,-
and because I stupidly sold my beloved SL1200 MK1 I bought a cheap direct driven Technics for 200,- again.
Everything not high class, but working very well.

The old CD-4 demods are mostly analog transistor circuits, should not be a big problem to rebuild such if you have a circuit.
Now I finished rewiring one of my 4VR5436 and at the next I will take a closer look at the signals at the checkpoints.

 

[jupp369]

The currently available software CD-4 demod doesn't demodulate anything. As I understand it the approach is to decode CD-4 as if it is matrix encoded. I don't see how that achieves anything more that running CD-4 through a QS decoder ie it is synthesised quad.

and it's working only with 96kBs, what means triangles instead a fine sine which you get with 192kBs

 

[kfbkfb]

The currently available software CD-4 demod doesn't demodulate anything.

???


There are 2 CD-4 demod/decode modes - the (original) "soft fail" mode is sort of the ultimate extension of the "Hi-Blend" option (on some Technics brand CD-4 demods) - channel separation is somewhat reduced in order to reduce distortion.

The Classic CD-4 decode mode has full channel separation in all directions at all times:
https://pspatialaudio.com/CD4_classic.htm
edit:
An AES paper describing the software CD-4 decoder:
https://www.aes.org/e-lib/browse.cfm?elib=20544The Needledrop Handbook contains a reprint of the AES paper:
https://pspatialaudio.com/NDH_book2.htm
Kirk Bayne

 

[par4ken]

It's a workaround to try to deal with the lack of new phono carts that work well for CD-4, probably all that would be needed would be a stereo cart w/good channel separation > 7.5kHz & Shibata stylus.

There are several new cartridges that will work. I recently bought an Audio Technica ART9XA. Expensive yes but works great.

 

[Owen Smith]

and it's working only with 96kBs, what means triangles instead a fine sine which you get with 192kBs

Irrelevant given the software it isn't actually demodulating the FM carriers.

 

[Owen Smith]

There are 2 CD-4 demod/decode modes - the (original) "soft fail" mode is sort of the ultimate extension of the "Hi-Blend" option (on some Technics brand CD-4 demods) - channel separation is somewhat reduced in order to reduce distortion.

The Classic CD-4 decode mode has full channel separation in all directions at all times:

That's not how it was described on QQ last time I saw any discussion about it.

 

[kfbkfb]

Mr. Brice explains his reasoning for developing the "soft fail" version of the software CD-4 decoder first early in the "Working..." thread, later in the thread, the availability of the "Classic" full separation decoder is announced.


Kirk Bayne

 

[MidiMagic]

That is the method they used to cut CD-4 records to not exceed the cutter frequency range. But the CD-4 cutter stylus is still needed.

I have quite a few turntables (including my favorite) that run at 16.67 rpm (the first speed Audio Books used). But a Shibata stylus is still needed to track the tiny wavelengths of the carrier. Halving the turntable speed does not change the size of the carrier motions of the stylus or the wiggles in the groove.

 

[kfbkfb]

But a Shibata stylus is still needed to track the tiny wavelengths of the carrier.

Exactly, or some other line contact type stylus, it seems to me that line contact stylus shapes are here to stay (although for some reason, cart makers don't point out that line contact stylus shapes are likely to contact some of the undamaged upper half of the record groove, thus making the record sound like new [in most cases]).


Kirk Bayne

 

[jaybird100]

would it not be easier to invest once in a CD-4 cartridge than humble around with so many variables?
I use a Nagaoka JT 322 CD4 cartridge, you may get it for 150,- till 300,-
and because I stupidly sold my beloved SL1200 MK1 I bought a cheap direct driven Technics for 200,- again.
Everything not high class, but working very well.

The old CD-4 demods are mostly analog transistor circuits, should not be a big problem to rebuild such if you have a circuit.
Now I finished rewiring one of my 4VR5436 and at the next I will take a closer look at the signals at the checkpoints.

Wouldn't one need a turntable that can play at 16 2/3rpm for this to work? I can't think of a single one, made today, that can support that speed, and most of the ones that were made with 16 2/3 as an option used ceramic or crystal cartridges that might not have enough top end to deliver the carriers.

 

[proufo]

This approach is of course the best way to go about ripping CD-4 albums. Too many things that can and do go wrong with the normal way. My try at this is still in the works.

I wonder if there is a way to modify the headers of a 24-48 half-speed captured track to convert it to a 24-96 file, avoiding a conversion that could or could not produce a different file.

 

[barfle]

Assuming a DSP algorithm exists that would demodulate the carriers (admittedly, I haven’t looked for one), the limiting factor here isn’t the frequencies involved, but the wavelength of the carrier in the recorded groove. I’ve heard that a Shure elliptical stylus can read it, but most users say a Shibata stylus is needed to detect and convert those very short wavelength signals to electricity.

@MidiMagic already reported this issue. But what the heck. If you try it and it works, share the joy!

 

[kfbkfb]

The Shibata stylus was designed for CD-4 and is still available on some new (stereo) phono carts.

The Stereo Lab software does support 1/2 speed needledrops:
https://pspatialaudio.com/half_speed.htm
(maybe someone here could get the demo version [which, IIRC, includes the CD-4 decoder] and try a 1/2 speed CD-4 needledrop)


Kirk Bayne

 

[MidiMagic]

There are plenty of turntables that came with the 16.67 speed:

- I have a Lenco L78 and I used to have a B55. Most other Lenco turntables also had 16 in the 1960s.

- Some Thorens models had 16, 33, and 45 and lacked 78. Thorens TD124 and TD224 have all 4 speeds.

- Garrard models: RC120, RC121, RC210, Type A, A II, AT6, AT6 II, AT40, AT50, AT60, A70, SP20, AT40 II, AT50 II, AT60 II, A70 II, SP20 II, SL55, and SL65.

- Dual made 1005, 1006, 1007, 1008, 1009, 1010, 1011, 1015, 1018, and 1019.

- Miracord made PW9, PW90, PW10, PW10H, PW16, PW40, PW45, PW50H, 620H, and 770H.

- Perpetuum Ebner made Rex Deluxe, PE66, PE2010, PE2015, PE2018, and PE2020.

- Collaro made TSC640, TSC740, TSC840, TC99, S60, and RP59.

- Glaser-Steers made GS77, GS300, and GS400.

- Rec-O-Kut had turntables with 16.

- Stanton had turntables with 16.

- VM, Webcor, BSR, Philips, RCA, Phonola, and others made units with 16 rpm but with lower quality arms.