Lou Dorren: A new CD-4 Demodulator!!! [ARCHIVE]

[loudorren]

Hello CD-4 and LP Fans,

Clemens,

I find it fascinating that these techno-rumors get started, become some sort of de-facto standard, and then promulgated. And now the techno-truth (sorry about the tongue and cheek).

The Shibata stylus was designed for one purpose and that was to reduce groove damage during playback. Originally it was thought that the 30KHz sub-carriers would wear faster than the lower frequency undulations. The reason was that a .7 mil conical or a .3 mil by .7mil elliptical stylus tracking at 1.5 grams exerts a tracking pressure of 15000 lbs. per square inch at the groove contact points. This point contact, after a number of plays on LPs and 45s, mono, stereo, or CD-4 will create a trough in the record groove at the contact point.

The Shibata stylus tracking at the same 1.5 grams exerts only 150 lbs. pressure on the groove at the line contact points. The line contact distributes the pressure over a larger groove area, thus significantly reducing record wear.

I would never play any of my record collection with any stylus other than a Shibata tipped one. One additional factor is that the Shibata tip will yield very satisfactory playback of damaged records because it will play the part of the groove that has not been touched by the point contact stylus.

With regards to stylus wear, you should already have figured out the answer. If the wear on the groove is reduced, the life of the stylus is increased. Actually, the Shibata tip will typically yield one order of magnitude greater life than any point contact stylus.

Scooping out emulsified dirt has no effect on stylus life.

Lou Dorren

 

[quady-de]

Hello Lou,
there is a private message for you in the members earea
plesase take a look.

thanks
Norman

 

[Tonedoev]

Will the new CD-4 demodulator have a volume control such that it can be coupled directly to power amps?

 

[Clemens]

Dear Lou,
Thank you very much for your reply regarding the stylus.
It is clear now.
Clemens

 

[loudorren]

Hello Quadraphony Supporters,

Tnoedev, The audio outputs are at consumer line level of -10 dBm. The is no output level control so you will have to use the aux input on a 4 channel control pre-amaplifier.

A general note to all,

The number of people that want the new demodulator has gone past fifty which means that the price is now $505.00 USD. Any body that is still contemplating should sign up soon. I would like to how many units to build by the end of the next two weeks for planning purposes. I will build a 10% overage to cover breakage, lost units, and stragglers. Also I am not sure of the extra cartridges and styli count so when I put up the request for service kits and spare parts I will ask for that count again. Don't send any addendum posts about cartridges or styli at this time.

The completion of the pre-production prototype is almost finished and after all performance tests will be shipped to Jon Urban for his evaluation.

Everything is looking excellent at this time.

Lou Dorren

 

[callmez]

Sounds great, Lou!

Can you provide approximate dimensions for the finished unit? I'm building a cabinet to house all my equipment and need to save space for it.

Thanks!

Mark Z

 

[proufo]

The completion of the pre-production prototype is almost complete and after all performance tests will be shipped to Jon Urban for his evaluation.

Whattabout the MkII?

Seriously, do you think there's room for improvement?

 

[loudorren]

Hello Quadrasuffers,

callmez, I won't have the final dimensions until the prototype is complete. This is due to any unforeseen circuit changes that may affect the final board size. I will have info for you shortly.

proufo, If I have done this correctly there should be no need for a MKII!


To every one, I am going to be in the recording studio for the next few days working on new CDs for 4 new artists that I have signed to my record label. I will check the thread to see any posts but I probably won't answer until Friday.

Until then, Audios, Videos, and Radios,

Lou Dorren

 

[kfbkfb]

Regarding the 15kHz CD-4 bandwidth limit:

http://www.codingtechnologies.com/products/sbr.htm
The higher frequencies are generated by the SBR
decoder, which is mainly a post-process following
the conventional waveform decoder.
Instead of transmitting the spectrum, SBR
reconstructs the higher frequencies in the decoder
based on an analysis of the lower frequencies
transmitted in the underlying coder.


Although the CD-4 analog signals don't contain the
"guidance information" for the SBR decoder, would
SBR still work and extend the CD-4 bandwidth above
15kHz?

Kirk Bayne

 

[Bonzodog]

Sounds like a variation of the Aphex Aural Exciter.

Patent

 

[Quadro-Action]

Hello Lou - for an answer after your work in the studio: A few of the fans here (Germany), which have made orders self or about me ask me now, if you have already ideas, ho the paying should work. For example with paypal or by international bank order etc.? Thanks for a tip. (Or have I overlooked something?)

Dietrich

 

[The Quadfather]

I wouldn't want any kind of tinkering in the CD-4 siugnal such as this SBR codec. 15KHZ is quite sufficient for me. Besides, I doubt it could be applied to an analog signal, though I admit I don't know much about it.

The Quadfather

 

[Bonzodog]

I wouldn't want any kind of tinkering in the CD-4 siugnal
The Quadfather

I agree, Quadfather. Just give us the most faithful reproduction possible.

If we want to futz with it, we can do that on our own time.

 

[Quadro-Action]

I think, that frequencies of 15 kHz are enough for a well listening - if we could. The most of us Q-fans will have meanwhile an age far about 30 (my age at the quadraphonic years). So the most of us could be happy to listen 10 kHz. And I think nevertheless to listen 20. Let your ear doctor make a measurement of your own frequency range - and you may shed some tears, but as I said above - you will feel, that you are by listening on the top.

 

[loudorren]

Hello all Quadraholics,

I read the post and just could not resist.

kfbkfb, Bonzodog, Quadfather , and Quadro-action,

Let me state that Ray and Dagmar Dolby are very good friends of mine. Ray is retired and does not run his company any more so what I am about to say does not reflect on him.

Spectral Band Replication (SBR), just writing it makes me gag. Here is another low fidelity band aid that is a technology joke. I particularly love statements like "appealing audio quality", "State-of-the-art perceptual audio codecs achieve "CD-quality" or "transparent" audio quality at a bitrate of approximately 128 kbps (~ 12:1 compression)", and one of the best ones:"using SBR in conjunction with mp3 (see below under mp3PRO) we can achieve a quality at 64 kbps stereo that compares to conventional mp3 at a bitrate of > 100 kbps stereo."

What absolute audio garbage. First lets look at CD quality sound. A 2 channel stereo CD uses a sample rate of 44.1KHz (meets the Nyquist rate nicely) and a resolution of 16 bits ( each sample has a possibility of 65536 levels). Each one of these level defines the amplitude and frequency content occurring at that sample. The end result is a bit rate of 1,411,200 bits per second. Adaptive, predictive (perceptual) encode-decode systems "compress" the original signal based on algorithms that assume a louder sound will mask a softer sound or the following bits are redundant and all do not need to be sent. Every bit sent is the homogenous product of 12 original bits (throw away data compression).

This technique works OK for cell phones but not for music. Here is a great demonstration that all of you can do. It requires a cell phone and a wire line phone. Find a phone number that has music on hold and compare the audio quality of the wire line vs the cellphone. Even though the phone bandwidth is only 300Hz to 3KHz, you will notice that on the wire line phone you can still hear all of the music in that range. With the cellphone you will notice that as the sound gets lower in level it becomes noise or disappears.

The SBR "system" goes even further by not even attempting compression of high frequencies. It "guides" the decoder to artificially generate the missing high frequencies. Generating complex FFTs ought to be interesting! After all of this spell binding technological witchcraft, as stated in the Dolby information: "we can achieve a quality at 64 kbps stereo that compares to conventional mp3 at a bitrate of > 100 kbps stereo."

Let me, If I may, translate that last statement for you: "we can achieve the same lousy audio quality at 64 kbps stereo as we get with conventional mp3 at a bitrate of > 100 kbps stereo." What a audio quality benchmark, MP3!

I must say again that this is no reflection on my friend Ray Dolby, only the people running the company now. Now at Dolby, it is quantity before quality or Low Fidelity sound bought to you by Dolby Labs.

Quadro-action,

When we take orders it will be by PayPal.

Off to Mixing,

Lou Dorren

 

[The Quadfather]

Incidently,the nyquist theorem states that the carrier frequency must be at least twice the highest modulating frequency to reproduce the modulating signal opun detection. It does not say that the ratio stated is optimal for fidelity. But this would matter more in AM modulation than in phase/frequency modulation. In a CD-4 record, you're pushing it to the limit. But it does an acceptable job of producing a difference signal. It's good enough to work. I'm happy with it.

The Quadfather

 

[loudorren]

Hello Quadraflectors,

Mixing is finished for the day.

Quadfather,

The Nyquist theorem states that to fully and accurately reproduce a signal, the sampling rate must be 2 times or greater then the sampled frequency. The 2X ratio is in fact optimal. Sampling at a higher then 2X rate does not improve the reproduction of that signal. It does however raise the maximum frequency that can be sampled. In CD-4 the lower sideband of the 30KHz sub-channel cuts off at 18KHz, while the main channel high frequency cuts of at 15.250 KHz. The frequency range between these two is the guard band to accommodate the stop bands of the low pass and band pass filters. To achieve the 15KHz response in the sub-channel SSBFM is employed on the upper sideband.

Modulation is a form of sampling regardless of the type.

The next question is "what about oversampling". The reason for oversampling is not for accuracy, it is to make the filtering easier to implement. With modern conversion techniques and low cost DSPs filter implementation is no longer a problem.

Lou Dorren

 

[watsontr]

Lou,
Just wondered what your opinion was regarding a suitable turntable for CD-4? I've seen mention that straight tone arms, modern turntables because of not necessarily having suitable impedance (I think relative to the higher frequency response) wiring and other reasons I can't recall at the moment, are not suitable for CD-4. I have a few turntables but I'm wondering what I may need to make the best of the new demodulator should I manage to get one.
Regards
Tom

 

[kfbkfb]

Regarding the RCA Quadulator CD-4 encoder:

(I just found this post by "cd4cutter")
http://lathetrolls.phpbbweb.com/lathetrolls-ftopic817.html
I was also the developer of the RCA Quadulator
which was the disc mastering signal encoder
required to cut the only discrete 4-channel disc
analog record ever manufactured, the CD-4 process.


Perhaps "cd4cutter" can help locate an RCA Quadulator
which could then be used (with a 1/2 speed record
cutting system) to create CD-4 master discs.

Kirk Bayne

 

[Lucanu]

Kirk, great find!!!!!!!!!
:banana: