CD-4 Ramblings and Tech Discussion

[flavio81]

Except all Klystrons are pretty much the same and have pretty much the same non-linearities. But all the ubiquitous Astatic or Tetrad or Electro-Voice or any other ubiquitous inexpensive ceramic cartridges mounted upon the equally-ubiquitous all-plastic Garrard or BSR record changers upon which the vast majority of Dynagroove pressings were played, do not have even CLOSE to the same distortions

Dynagroove (and other pre-distortion methods) correct for the distortion created by a conical stylus of a specific radius (typically 0.7mil). The ubiquitous ceramic cartridges and the ubiquitous cheap magnetic cartridges and other ubiquitous cartridges use EXACTLY the same ubiquitous 0.7mil conical stylus, which will produce EXACTLY the same tracing distortion that the pre-distortion system is trying to cancel.

[flavio81]

And then what? Twin-track the disc with two grooves one-groove-width apart from one another and have a four-pole twin-stylus cartridge?

Non-sequitur. I never proposed such a thing. I was talking about a four-channel digital audio file as a quad medium. A digital file to be played with a PC and a DAC.

Except the ``high bandwidth'' would have to be ridiculous in terms of a sample rate.

As we all know, the MINIMUM sample rate required to capture an analog signal into digital is twice the highest frequency

Yes. Thus you'd need 100KHz sampling rate to safely capture non-decoded CD-4 audio.

In reality though, trying to get an even CLOSE to accurate sampling of a sine wave with only two samples is absolutely ridiculous.

No. Unless you want to believe what some audiophile magazines (devoid of science and common sense) publish.

Ten-times or a hundred still wouldn't give you THAT good of a sampling. A thousand times BEGINS to approach acceptability.

No, that isn't true. Review the nyquist sampling theorem.

But in order for the computer to EFFECTIVELY capture the CD-4 tone ALONG with all of it's modulations, the computer would have to sample at a minimum of 900 KHz, 9,000 KHz or 90,000 KHz (of ten times, a hundred times and a thousand times respectively of twice-the-highest-frequency needed for sampling).

No, that isn't true. Review PCM and its theory.

The only computer that can do that on a regular basis is the Cray Supercomputer Arrays(...) recording engineers were back in the mid `50'(...) millions and millions of punch cards (...) Nothing more. Baby simple. (...) Dropped into Bernstein's Omnibus show from the 50's

That is not relevant. Please stay on topic.

And then back to our other topic, the main problem with the ORIGINAL CD-4 system was NOT the mis-placement of the RIAA curve or the NAB curve from the tape being wrong,

I never said such a thing.

Then, due to various ``bumps'' and ``valleys'' in the not-perfectly-flat response of the cutterhead in question, rather than adding a nice pleasing effect to a vocal or lead instrument, this will now mess with the frequencies in the high-bass or low-midrange areas, making the recording sound terrible in comparison to standard stereophonic releases cut on the same lathes in the same period.
Which, especially in the early days of CD-4, they often did, but people forgave a lot in order to have double the channels.

1. Feedback cutters, which exist since 1958, do have a perfect flat response from 40Hz to at least 16KHz, providing you use enough feedback.
2. Half-speed cutting was already perfected by the Decca/Telefunken team in 1958. That's what they used to master the Decca FFRR records.
Let me say it again. Half speed cutting problems were already solved.
In 1958.
With a prehistoric Neumann cutting head.
Which was so old it wasn't even branded "Neumann" but "Telefunken-Decca"
Which was so old its armature wasn't even 45-45 degrees but horizontal-vertical.
Go listen to those Decca/London FFRR records. They sound beautiful. They do have enough bass.

So that's why you really couldn't master the ``two-channel modulated program'' into the computer the conventional way and retrieve the signals digitally, even if you HAD a program to do so.

You were talking about cutting records at half speed and now you're talking about transcribing CD4 records to digital. Non sequitur!

But Jamie Howarth at www.plangentprocesses.com does similar work with their proprietary-at-the-moment technology for retrieving bias frequencies off master tapes and using that to create an inverse sync and run a computer off that newly-created inverse sync without actually having to capture the original supersonic bias to do so.

Well, they DO capture the supersonic (>60KHz) bias. Which, curiously enough, is what you just said it was practically impossible to do on your last post. And no, they don't use a hyper expensive Supercomputer to do it. It can be done with a 192KHz DAC if you play the tape at half-speed. So there you are, they capture bias frequencies of over 100KHz with a 192KHz DAC. Don't believe me, believe the very same Jamie Howart:

http://www.gearslutz.com/board/6302179-post19.html

You just posted that for capturing the 50KHz bandwidth of CD4 you need 90000KHz of sampling frequency. This isn't true. Thus, i insist you should check out the Nyquist sampling theorem. Science, it works.

[dlaloum]

I hate to say it...

There is no rhyme or reason to an Analogue CD4 medium today.

Producing new multitrack recordings - you might as well use the DVDA format... or any of the current PC audio multitrack container formats.

Any CD4 on vinyl will struggle with all the compromises involved, and will be compromised by it in the end.

Which is not to say we should not have CD4 rigs - the vintage material is there and should be enjoyed!

If someone is already making a multi-track recording and wants to issue it in CD4 for those who prefer the rituals of analogue to those of digital - cool!
But it is just a fun thing to have and not an attempt to produce something superior.

Standard stereo LP's can sound superb, and do so to a substantial degree because of the efforts that went into making CD4 work - they led to a quantum jump in record technology/capabilities throughout the chain.

Let's face it - Digital is superior in 99.9% of cases and almost all top end recordings today are done digitally...

Producing CD4 recordings today is like producing Pianola rolls.... nothing wrong with it and good fun. But lets not stress about it!

bye for now

David

[flavio81]

Hi David, i understand your point. But for example we can say "what is the point on releasing LPs from a digital master today?" Yes, there is a point, as i've said before: First, the LP is a good enough medium to transport such audio with no subjective loss of quality. Second, people who have a high-end turntable system not necesarily have a high-end D/A converter. Third, the LP medium is aesthetically more pleasant.

So that above applies to stereo records, and i'd venture to say it can also apply to CD4 records. It looks as a complex system, David, but isn't THAT complex. In any case, yes, let's do it for fun.

Greetings! Nice to see you in this forum too!

[proufo]

I hate to say it...

There is no rhyme or reason to an Analogue CD4 medium today.

Sure there is. For fun!

And for going broke. Each Lp would cost a fortune.

[proufo]

Saludos estimado Pablo,

Well, i'm no expert (nor amateur!!) at DSP processing but there are algorithms to do dynamics compression and decompression in the digital domain. If i recall correctly, for ANRS you'll want to filter and divide the input in two spectrums (easy to do in the digital domain), and then apply different compression ratios to them.

Hola de nuevo, Flavio.

It seem to be more complex than compressing and decompressing, as the processing is frequency-dependent.

I did some searching on the basics and got stuck at ANRS.

[proufo]

Except the ``high bandwidth'' would have to be ridiculous in terms of a sample rate.

Hello ndiamone.

I don't follow this.

Won't 24/96 capture up to 48 Khz?

I believe there are people here that have made digital files of CD-4 records and played them through a demod with success.

Would that prove anything?

[proufo]

I'm not sure that the above approach does not take my thoughts into consideration.

The thing that matters most to me is the fidelity, tonality, and warmth of the finished product. I may be reading more into this than is implied, but working in the digital domain without those three things leaves me wondering if going to the trouble of recreating a CD-4 type vinyl is worth the effort?

Hello ress.

Looking for aural bliss in CD-4 reproduction may not be a good bet.

Hopefully, we will soon see if Lou's demodulator brings us a step closer.

Given the advances in digital recordings and players, maybe the optimum path is to process existing mixes and play back via DVD-A/SACD media. Or digital files. Just as the generous converters already do now.

Anally, I'd love to have digital recordings done from two-channel, but I'm sure using a four-channel recording from a good demod would be virtually the same or better, as a starting point. What would be needed is to assess the compromises made for CD-4 cutting and compensate for them as possible, all in the digital domain.

[proufo]

Third, the LP medium is aesthetically more pleasant.

And tweakable to taste, for better or for worse.

[dlaloum]

hmm and no need to waste too much space - CD4 is 15k bandwidth limited - so digital version would be either 1x24/96 (to 48kHz) or 2x24/32 (to16kHz)

2 x 24/32 will take less space and be easier to play back (no decoding) - but harder to create (has to be decoded into the file packages)

[ndiamone]

I don't follow this.Won't 24/96 capture up to 48 Khz?I believe there are people here that have made digital files of CD-4 records and played them through a demod with success. Would that prove anything?

Doing it at ALL and doing it WELL are two different things.

Remember, at 96K there's only two samples per cycle of the highest frequency, which would indeed be 48K. The CENTER FREQUENCY of CD-4 is 30K, then it modulates down to 20K and up to 45K. So it depends on how good of a resolution you want for the top end of the albeit-limited program bandwidth, but also how good of a resolution you want for the top end of your demodulation frequency. See below under ``resolution''.

Yes. Thus you'd need 100KHz sampling rate to safely capture non-decoded CD-4 audio.

At the very minimum, yes.

No. Unless you want to believe what some audiophile magazines (devoid of science and common sense) publish.

Simple arithmetic will prove that statement incorrect, as I posted previously. The LOWEST resolution you can get is 2x highest frequency for digital sampling. However if you have only two snapshots of the peak of one wave and the valley of the other, it gives almost no characteristics of the spaces between the two samples, just where they ended up at, not how they got there.

The only thing you can capture perfectly in digital with two samples/cycle is a pure sine, square, saw, etc wave.

No, that isn't true. Review the nyquist sampling theorem.

Which, again goes to the MINIMUM sampling rate, and then only for a pure sine wave, nothing with any modulation in it.

It's the same as in film or TV. If all you needed was the minimum, why have they developed 1080p and why are they developing in Japan 16K ganging together multiple 4K or 8K scanners and now the newest ones 24K scanning when supposedly 2K scanning is already smaller than the film grain resolution it's trying to capture?

But in order for the computer to EFFECTIVELY capture...

No, that isn't true. Review PCM and its theory.

Which, again only gives MINIMUMS otherwise why would there be 24/96 STEREO ONLY DVD Pro-Audio etc (nevermind 5.1). EVERYBODY can't be a ``stereophile-idiot''.

The only computer that can do that on a regular basis is the Cray Supercomputer...

That is not relevant. Please stay on topic.

Kid, you get on my nerves. You ask a question about sampling CD4 into a computer EFFECTIVELY and getting a good result, then you whine and cry and argue and complain with engineers who have been in the field since before you were born. If you knew the answer, why did you come here to ask us for?

1. Feedback cutters, which exist since 1958, do have a perfect flat response from 40Hz to at least 16KHz, providing you use enough feedback.

Whatever book you got that out of is incorrect. And even if it WERE correct, that STILL gives problems in the lower ends of the bass and the higher ends of the treble in REAL TIME nevermind half-speed or 2/3rds speed or 3/4 speed (i.e. cutting at 33 for 45 playback).

Go over on the Lathe Troll Forums http://lathetrolls.phpbbweb.com/lathetrolls.html and make that same statement and see how fast you get ROUNDLY trounced.

2]. Half-speed cutting was already perfected by the Decca/Telefunken team in 1958....They do have enough bass.

Wrong again. You even agree there's bass problems in the technology on your OWN POST! http://www.diyaudio.com/forums/analo...ml#post2585729. I suggest you go check out the
Lathe Trollers or any of the other ``prehistoric'' cutting forums populated by ``prehistoric'' engineers that have been in this field since before you were born and see the responses you get.

Or, better yet, go call up Steve Marcussen or Doug Sax or Bernie Grundman or anybody like that and see what kind of response you get from them .

So that's why you really couldn't master the ``two-channel modulated program'' into the computer....

1]. You were talking about cutting records at half speed and now you're talking about transcribing CD4 records to digital. Non sequitur!

This is your Disneyland Storyteller. You can follow along in your book.
Just turn the page when you hear the :raspberry:.

The rest of you guys, if you want to laugh, go slide down to some of his other posts in the DIY and other related forums he belongs to and see how He Can't Handle the Truth.
http://www.diyaudio.com/forums/analo...ml#post2585794 :LOL: Like we live to prove a kid wrong. Please.

2]. Well, they DO capture the supersonic (>60KHz) bias...And ...it can be done with a 192KHz DAC at half-speed. http://www.gearslutz.com/board/6302179-post19.html

Which gives you the same problems with the audio as capturing or recording at half speed does everyplace else without newer technological improvement.

Gearslutz. :LOL: :raspberry:.That's like saying you get all your World News from the National Enquirer.

And, you'll notice in Jamie's response that conventional electronics you espouse so fondly are a hit-and-miss affair AT BEST nevermind anything anybody would actually advise using.

Pick a side, kid and stick with it. You can't play both sides on the middle.

2]. You just posted that for capturing the 50KHz bandwidth of CD4 you need 90000KHz of sampling frequency. This isn't true. Thus, I insist you should check out the Nyquist sampling theorem.

Like you should read your Gearslutz :LOL: postings more carefully before you include them in your argument.

Kids and their book-learning. . Kayyyyyyyy....next topic!

There is no rhyme or reason to an Analogue CD4 medium today.....

Like nobody should be wasting time and money making brand-new Edison cylinders either with modern music on (Madonna on a 4-minute Amberol anybody?) and a hundred other things.

Which is not to say we should not have CD4 rigs - the vintage material is there and should be enjoyed!

If someone is already making a multi-track recording and wants to issue it in CD4 for those who prefer the rituals of analogue to those of digital - cool! But it is just a fun thing to have and not an attempt to produce something superior.

Sure it is. Just like the people who are STILL to this day trying to improve on C Y L I N D E R technology TO USE. Nobody spends millions of research and development dollar or grant monies ``for the fun of it.''

Standard stereo LP's can sound superb, and do so to a substantial degree because of the efforts that went into making CD4 work - they led to a quantum jump in record technology/capabilities throughout the chain.

No aregument there.

Let's face it - Digital is superior in 99.9% of cases and almost all top end recordings today are done digitally...

Well the second half of that is right. If the first half was right, they wouldn't STILL be making eight-track two-inch recorders that are ALL-TUBE besides.

I know what the mastering engineers are saying, that it's only when you try to overdrive an amp that you can tell between the solid state/digital technology that amplifies the ODD harmonics, giving the music an edgy feel vs. that of the tube amp which amplifies the EVEN overtones giving the music a warmer feel, but how many engineers even in those days liked to stay within parameters?

Producing CD4 recordings today is like producing Pianola rolls.... nothing wrong with it and good fun. But lets not stress about it!

And there are companies today making a VERY good living at producing reproductions of all kinds of vintage technology from piano rolls (I have Gloria Estefan doing Bad Boy from Three Men and a Baby soundtrack done in a Gay 90's music-hall style and cut for a player piano that has all kinds of band attachments to it - horn section drum section, xylophone section, you name it.

I put it up and play it for company just to trip people out next to my Madonna Blue Amberol cylinder re-creation of her singing Crazy for You from Vision Quest on a restored 1925 player.

Claghorn here Senator Claghorn that is. I'm from the South. I'll never go to the Yankee Stadium `less `en it's a Southpaw pitchin. That's a joke, son. Get to laughin'. Don't all you kids be a-pooh-pooh-in' people's efforts so fast to be bringin' back and improvin' vintage technologies. Set-a-spell and ya might ah-say ya might learn somethin' boy.

[flavio81]

Hola de nuevo, Flavio.

It seem to be more complex than compressing and decompressing, as the processing is frequency-dependent.

I did some searching on the basics and got stuck at ANRS.

From H.H. Lou Dorren's magnific paper on his demodulator:

"The ANRS has a variation on the basic compander. It divides the companding scheme into two frequency
bands. This technique is similar to Dolby C noise reduction with the exception that the frequency bands
for CD-4 ANRS are different than Dolby C. The CD-4 has a low mid compressor that has a mid bandpeak at 630 Hz and a high band compressor with a peak at 15KHz."

http://www.johana.com/~johana/dorren/cd-4paper4.pdf

So correcting what i said before: Seems that what you do is you filter the input applying two different EQ curves (the one with the peak at 630Hz and the other with the peak at 15KHz) and the amplitude obtained after passing the input through the combination of said curves is the amplitude to feed the compressor with. In other words, the control signal for the compressor.

The idea is to achieve more noise reduction at one band vs the other.

[flavio81]

Hello ndiamone.

I don't follow this.
Won't 24/96 capture up to 48 Khz?

Yes, it will. To claim otherwise, is wrong.

[flavio81]

Wrong again. You even agree there's bass problems in the technology on your OWN POST! http://www.diyaudio.com/forums/analo...ml#post2585729. I suggest you go check out the
Lathe Trollers or any of the other ``prehistoric'' cutting forums populated by ``prehistoric'' engineers that have been in this field since before you were born and see the responses you get.

Or, better yet, go call up Steve Marcussen or Doug Sax or Bernie Grundman or anybody like that and see what kind of response you get from them .
This is your Disneyland Storyteller. You can follow along in your book.
Just turn the page when you hear the :raspberry:.

The rest of you guys, if you want to laugh, go slide down to some of his other posts in the DIY and other related forums he belongs to and see how He Can't Handle the Truth.
http://www.diyaudio.com/forums/analo...ml#post2585794 :LOL: Like we live to prove a kid wrong. Please.

Which gives you the same problems with the audio as capturing or recording at half speed does everyplace else without newer technological improvement.

Gearslutz. :LOL: :raspberry:.That's like saying you get all your World News from the National Enquirer.

And, you'll notice in Jamie's response that conventional electronics you espouse so fondly are a hit-and-miss affair AT BEST nevermind anything anybody would actually advise using.

Pick a side, kid and stick with it. You can't play both sides on the middle.Like you should read your Gearslutz :LOL: postings more carefully before you include them in your argument.

Kids and their book-learning. . Kayyyyyyyy....next topic!

This is way off topic and you are making an ad-hominem attack, not to mention your lengthy ramblings on things that are not relevant to this topic.

This is a forum for technical discussion, not for flame wars or lengthy self-aggrandizing autobiographical ramblings. It is not a blog but a forum. And we're discussing CD4 demodulation. You should at very least stay on topic.

I'll leave the rest of the participants in this forum -who ARE staying on topic and contributing valuable thoughts- to decide who is participating here because of a genuine interest in CD4 audio, and who is not.

[JonUrban]

Please treat each other with respect or I'm going to nuke any post that is not related to the new Lou Dorren CD-4 demodulator. You are free to start your own thread on your own philosophies.

[flavio81]

Hi Folks,

I recently managed to get my hands on a Panasonic SE-405 / EPC451C combo
2) High Frequency rise of about 8db (don't know whether this is typical, I would have expected Frequency Response to be flatter?)

David,

Sorry for not reading this post of yours. On VE i've uploaded a review of the EPC-450C-II, you can see that the frequency response published there has what it looks like a shelf-filter 5.5dB rise from 15KHz. Then it stays healthily up at that level. I bet this was intentional to help with carrier recovery. I can read your mind and i bet you are currently thinking on what is the resonance freq of that cart ... Your guess is as good as mine, but if i was the cartridge designer i'd choose 38KHz as the res freq, since that's the center of the carrier freq.

On your SE-405 you have a rather sharp filter after 15KHz, so the combined freq response of your EPC451C with the SE-405 will have a "bell" at about 15KHz. Not nice... That's why you should better try Lou's preamp or my cheap and dirty preamp schematic. In any case, i'm 100% sure your channel imbalance problem is on the preamp, not on the cartridge, so Lou's demodulator/preamp should not show that problem.

PS: Maybe you would like to read US patent #3975025, it is the patent for that cartridge

Let's discuss this on VE, since we're going off topic. Greetings!!
Flavio.

[dlaloum]

Hi Flavio,

the SE405 suddenly lost a channel so I pulled them out and decided to wait for LouD's decoder.... alternative being to use your circuit diagram.... but I am hesitant to get into soldering/making electronics....

So for now the EPC451C is lying idle..... waiting....

David

[The Quadfather]

CD-4 is a quality medium, not like old grammophone records. It was invented at the pinnacle of the analog phonograph recording technology. And it improved on it. When it is set up right, it can sound just as warm as a stereo LP, only in quad. And I think that it can be improved. That is why it should be attempted by anyone who cares enough to do so. But it would be a labour of love. Just as is Lou's demodulator.

The Quadfather

[flavio81]

I did some searching on the basics and got stuck at ANRS.

Hi again,

From what i've read today, ANRS (as used on JVC cassette recorders) was directly compatible with Dolby B. It seems that it was JVC's way of incorporate Dolby B without paying royalties... and JVC lost some lawsuits to Dolby Laboratories because of this!!. If this ANRS used on JVC's cassette recorders is exactly the same ANRS that is used in CD-4, then you can use dolby B decoding, which is well documented elsewhere.

BTW they had a "Super ANRS" system which... seems to be Dolby C in disguise. LOL!!