....to decode cd-4 lps with a pc software???
Is there a way....
- Thread starter Lucanu
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Lucanu said:
Not at the moment, the FM subcarrier poses the most difficult part of the process, it is not as simple as just mixing.
Malcolm
mandel
Well-known Member
I can't see any reason why this wouldn't be possible. Recording at 96khz would keep the subcarrier perfectly intact (if I understand Mr Nyquist correctly). Some guesswork would be necessary for the width of the bandpass filter and how much of the front-back signals to mix into the normal stereo tracks. I *think* I know the software that *may* be able to achieve this, a program called Sampled that has some FM options and basic calculus processing. I dont have a CD-4 disc to test it with. Given a 96khz sample i may be able to figure something out.
That said there are far more experienced people who'd probably be able to fathom it out easier than me. :xp:
That said there are far more experienced people who'd probably be able to fathom it out easier than me. :xp:
I don't remember the fellows' name on here, but he sent a Quadradisc onto his computer using Cool Edit Pro, and with the bandwidth display graph, you could easily see the musical signal AND the FM sub-carrier signal.
It's a fairly simple process, if people can figure out software SQ decoding, I'm positive a CD-4 variant can be done!
It's a fairly simple process, if people can figure out software SQ decoding, I'm positive a CD-4 variant can be done!
Q-Eight said:
Well that was me, and I did sample at 96Khz 24 bit. it all worked fine, even to the point of replaying (attenuated of course) back through the demodulator. It decoded well, albeit a little noisy. Unfortunately demodulation is not a simple process, the 30K subcarrier has to be demodulated, the ANRS has to be applied to the resultant difference signal. The easy part is the addition/subtraction of the baseband (Front + Rear) and the subcarrier (Front - Rear) to give the relevant signals. There is software available to demodulate fm broadcast signals, but the subcarrier is AM modulated not FM, and at 38 KhZso this is of little use.
A nice project for someone.
BTW here is a recorded CD-4 lp sample
Green trace - start of track,
Red trace - part way through medium level
Blue trace - start of high level band, note the massive increase in high frequency level
Yellow trace - Peak level on that track, Extremely high deviation, very high levels drifting down into the "normal" frequency band even.
Malcolm
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mandel
Well-known Member
Oh I've always read it was FM. Shame. What is ANRS?
mandel said:
ANRS is Active Noise Reduction System, think of it as a "Dolby" like system, frequencies are booosted on recording, split into 3 (I think) frequency bands. They are reduced on playback, reducing noise level in the subcarrier channel.
Malcolm
@malcolm2010
Which are the softwares you mentioned for demodulate?
Which are the softwares you mentioned for demodulate?
Lucanu said:
I assume you mean to demodulate FM broadcasts, this is not purely software based, you need some hardware to interface to a sound card or DSP chip. This is basically a receiver with the final stages ommited.
Search for "Software FM demodulation" there are a number of solutions.
Malcolm
Thank Malcolm2010 for your answer....
I do perform a Google search and I found something interesting. It's called SDRadio (www.sdradio.org), a freeware tool that make lots of operation for demodulate audio signals in real time. Just take a look and make some tests.
I do perform a Google search and I found something interesting. It's called SDRadio (www.sdradio.org), a freeware tool that make lots of operation for demodulate audio signals in real time. Just take a look and make some tests.
Disclord
900 Club - QQ All-Star
CD-4 didn't use just FM modulation for the back channels - it used FM in the low frequencies, Phase Modulation (PM) in the midrange which then went back to FM for the high frequencies. The A.N.R.S (Automatic Noise Reduction System) was JVC's answer to Dolby B - unlike Dolby B's single band, however, it worked in two low-level bands and was originally developed for Compact Cassette recording. JVC ended up paying royalties to Dolby for it (much like Sony pays royalties to Dolby for ATRAC used in MD and SDDS).
The A.N.R.S was ALWAYS part of the CD-4 system (some have claimed it was added later). Think how good CD-4 could have sounded if dbx Type II noise reduction had been used for both the Front AND back channels!
Vinyl lovers really owe a debt of gratitude to JVC for CD-4 - it spurred recording and playback improvements galore. And we wouldn't have had Half-Speed Mastering without it! Towards the end of the Quad era, CBS and JVC were talking about combining their respective systems. CBS had Universal SQ (USQ) and with CD-4 (USQCD-4????) a fully SQ Stereo/Quad Matrix/Full-Logic/Full-Discrete disc could be produced. With the introduction of the Ghent Microphone, USQ became a Kernel encoding system capable of producing full, unambiguous imaging like the Ambisonic Universal HJ format.
The A.N.R.S was ALWAYS part of the CD-4 system (some have claimed it was added later). Think how good CD-4 could have sounded if dbx Type II noise reduction had been used for both the Front AND back channels!
Vinyl lovers really owe a debt of gratitude to JVC for CD-4 - it spurred recording and playback improvements galore. And we wouldn't have had Half-Speed Mastering without it! Towards the end of the Quad era, CBS and JVC were talking about combining their respective systems. CBS had Universal SQ (USQ) and with CD-4 (USQCD-4????) a fully SQ Stereo/Quad Matrix/Full-Logic/Full-Discrete disc could be produced. With the introduction of the Ghent Microphone, USQ became a Kernel encoding system capable of producing full, unambiguous imaging like the Ambisonic Universal HJ format.
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