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Stereo or Mono?
2Bdecided
post Aug 31 2012, 11:37
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QUOTE (dc2bluelight @ Aug 30 2012, 05:28) *
Just one more comment...I recently heard a mono recording on the thing in the picture, the large cabinet with the horn on top. That's a phonograph without any electronics, all acoustic. The recording was made with an all acoustic recorder, no electronics either. It was, simply, astoundingly good! Don't think I'd want to hear all my music that way, but it was loud, clear, clean, and quite dimensional.
The thing can be seen and heard here: http://www.pavekmuseum.org/
There are much better gramophones (phonographs)...
http://www.youtube.com/watch?v=_MA957TfmIs
smile.gif

Cheers,
David.
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Arnold B. Kruege...
post Aug 31 2012, 11:39
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QUOTE (dc2bluelight @ Aug 31 2012, 01:47) *
QUOTE (pdq @ Aug 30 2012, 15:25) *
QUOTE (dc2bluelight @ Aug 30 2012, 13:42) *
It's a bandwidth thing, the L-R info is centered around a 38KHz suppressed carrier...

Not quite correct. The L-R signal is actually single sideband, from 38 kHz down, not centered on 38 kHz. The suppressed 38 kHz carrier is generated by frequency-doubling the 19 kHz pilot signal.

Beg to differ, it's still pretty much double sideband suppressed carrier centered at 38KHz, always has been.


Agreed. FM stereo was designed to be decoded by very simple means. I'm not sure that I ever saw a decoder based on just one tube, but definitely saw many based on two (and some germanium diodes). That's just four sections of gain, which is pretty slim pick ins.

QUOTE
And no, the carrier isn't technically a simple doubling of the pilot, but it is phase-locked to the pilot, and pilot to subcarrier phase is darn critical.


I have seen a number of FM stereo decoders that full-wave rectified the pilot and bandpass filtered the result to create the 38 KHz. I would call that doubling.
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Arnold B. Kruege...
post Aug 31 2012, 11:43
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QUOTE (2Bdecided @ Aug 31 2012, 06:37) *
QUOTE (dc2bluelight @ Aug 30 2012, 05:28) *
Just one more comment...I recently heard a mono recording on the thing in the picture, the large cabinet with the horn on top. That's a phonograph without any electronics, all acoustic. The recording was made with an all acoustic recorder, no electronics either. It was, simply, astoundingly good! Don't think I'd want to hear all my music that way, but it was loud, clear, clean, and quite dimensional.
The thing can be seen and heard here: http://www.pavekmuseum.org/
There are much better gramophones (phonographs)...
http://www.youtube.com/watch?v=_MA957TfmIs
smile.gif


Acoustic phonographs were made through the early 1950s. Some were child's toys, but some were larger and had a more serious intent. My recollection is that they sounded a lot better than that partially because they could be used to play 78s that were made by more modern means.
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pdq
post Aug 31 2012, 14:20
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QUOTE (Arnold B. Krueger @ Aug 31 2012, 06:39) *
QUOTE
And no, the carrier isn't technically a simple doubling of the pilot, but it is phase-locked to the pilot, and pilot to subcarrier phase is darn critical.


I have seen a number of FM stereo decoders that full-wave rectified the pilot and bandpass filtered the result to create the 38 KHz. I would call that doubling.

Agreed. PLL for generating the subcarrier was a relative late comer. I certainly never came across one in the '50s or '60s.

I stand corrected, however, on the SSB vs. DSB issue. blush.gif
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dc2bluelight
post Aug 31 2012, 15:59
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QUOTE (Glenn Gundlach @ Aug 31 2012, 02:38) *
"Extreme channel separation" recordings are often better described as multi-channel mono as the 'stereo' effect is created in the mixing console. When viewed on and X-Y phase display will be mostly an oval.
I like to describe the display as a "rats nest" because the X and Y inputs are uncorrelated. With true stereo, the greater the physical separation of mics the more random phase is displayed. To the extreme, coincident "stereo" and M/S shows almost no out of phase material and is heavily correlated, spaced omnis, like you'd use for a big pipe organ recording (private ;-) to GG), shows lots of random and out of phase material. X-Y displays show LF phase more easily than HF, so the greater the spacing, the lower the frequency that phase differences can occur, and the easier to see on that display. It's very very hard to make the correlation between an X-Y display and what is audibly "good", except in the extremes. But you knew that.
QUOTE (Glenn Gundlach @ Aug 31 2012, 02:38) *
This used to be VERY common given the technical limitations of stereo FM and LPs.
Not exactly sure which tech limits you're referring to, perhaps vertical groove limits, but I'll guess that the multi-mono craze of the 60s and early 70s had to do with the invention of multi-track recording and the desire by producers/engineers to gain more control. The hard-panned "ping-pong" mixes probably helped sell stereos because the effect was so obvious, if obnoxious.

QUOTE (Glenn Gundlach @ Aug 31 2012, 02:38) *
The absolute WORST in my opinion is 'synthesized' stereo. Some are done by comb filtering frequencies and putting the complement on the other channel. The absolute worst I heard - and the discarded the disc - had most of the lows on the left and the highs on the right. THAT "engineer" didn't have a clue.

G

If by "discarded the disc" you mean "blew it up with a shotgun", I applaud you. I had an unfortunate brush with a so-called "stereo synthesizer" at an FM station in a small market that desired to present stereo material 100% of the time, but lacked enough stereo hardware to do it. They stereo-ized mono commercials. What that was supposed to accomplish still evades me. I hope the box has long since found its way to the scrap yard. My only regret is not witnessing its melt-down personally.
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dc2bluelight
post Aug 31 2012, 16:29
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QUOTE (Arnold B. Krueger @ Aug 31 2012, 05:39) *
I have seen a number of FM stereo decoders that full-wave rectified the pilot and bandpass filtered the result to create the 38 KHz. I would call that doubling.

True, but pilot phase in that topology was a cruel master. Probably why PLL surfaced as soon as it was practical. I think I had a Heathkit tuner that did it the rectifier way, separation was terrible. Keeping that circuit aligned within a degree of phase is...oh you get the idea. It would also suffer more from multipath affects to the stereo demod than a PLL, since pilot to sub phase depends on circuit stability, where a PLL is, well, a phase-locked loop.

So, ok, technically doubling was used, but it didn't win, and the analog state-o-da-art ends at some form of PLL.
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2Bdecided
post Aug 31 2012, 17:13
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QUOTE (Arnold B. Krueger @ Aug 31 2012, 11:43) *
Acoustic phonographs were made through the early 1950s. Some were child's toys, but some were larger and had a more serious intent. My recollection is that they sounded a lot better than that partially because they could be used to play 78s that were made by more modern means.
But you're in America - you never had the three best acoustic machines over there wink.gif Sadly the clips on YouTube don't do them justice.

(HMV 203 / 202, Expert Senior, EMG Xb)
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dc2bluelight
post Aug 31 2012, 17:29
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In the US, FM Stereo Multiplex was approved by the FCC in 1961. The first reference I could find to an integrated circuit PLL demod design was dated 1972. Assuming no PLL demod existed prior to 1972 (not definite, might have been a discrete implementation), we have 11 years of FM stereo using only pilot frequency doubling demods. Then we have 40 years of PLL designs. Sure, it started out slow and there were no doubt a few doubling demods made after 1972, but several things happened then. For the first decade, FM stereo, and FM in general was shockingly unpopular. There were very few FM car radios, and most of them were quite poor. FM listenership was a tiny fraction of the total radio audience, and stereo receivers were available and sold, but relatively few in number. Then the 1970s started. First, ICs became common. But the driving force behind the proliferation of stereo radios and the PLL design was the fact that FM as the definitive music broadcast medium took off finally beating AM roundly for composite listenership numbers. FM in cars became pretty much standard, then required, so FM receivers finally proliferated, putting it mildly. The automotive market alone would have done the job, but component stereos in the home also became more commonplace too. They had to be cheap, good, and stable.

Overall, the number of PLL demods that have ever existed in the world is orders of magnitude greater than pilot-doubling demods. The technology has covered 40 years, including the FM boom and IC based designs, is inherently more accurate, stable and cheaper. Frequency doubling demods were pretty much abandoned with perhaps a few esoteric exceptions.

You guys are correct, pilot doubling was used. But this is why I reference the PLL method, and didn't give much thought to pilot frequency doubling. It simply became a non-factor for most of the history of FM, and PLL was/is overwhelmingly the standard.
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pdq
post Aug 31 2012, 18:05
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But isn't PLL just one technique for pilot frequency doubling? I don't understand your distinction.
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dc2bluelight
post Aug 31 2012, 19:18
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QUOTE (pdq @ Aug 31 2012, 12:05) *
But isn't PLL just one technique for pilot frequency doubling? I don't understand your distinction.

Frequency doubling is using a filter to isolate a harmonic of the original. So the 19KHz pilot is deliberately distorted so that the second harmonic can be selected, filtered, and used as the missing 38KHz carrier. The phase of the resulting 38KHz carrier is dependent on the filters involved, which if built with less than ultimately stable parts, can cause its phase relationship with the pilot to change, to the detriment of channel separation.

A phase-locked loop starts with a voltage controlled oscillator at some multiple of the desire frequency, then through a divider chain divides it down to 19KHz. A phase detector compares it to the pilot, detects phase errors and translates the error into a control voltage that is fed back to the oscillator which is then adjusted so that the end result is an oscillator phase locked to the pilot. A tap on the divider chain at 38KHz is chosen and that frequency used as the required 38KHz signal to control the demodulator. There are control loop filters, and other filters involved, etc., but that's the general idea. The entire thing has been on a single chip for decades, but can also be realized with less fully integrated means. To be fair, a PLL has opportunities for drift too, but they are easier to engineer out.

This post has been edited by dc2bluelight: Aug 31 2012, 19:20
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Arnold B. Kruege...
post Aug 31 2012, 20:03
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QUOTE (dc2bluelight @ Aug 31 2012, 11:29) *
QUOTE (Arnold B. Krueger @ Aug 31 2012, 05:39) *
I have seen a number of FM stereo decoders that full-wave rectified the pilot and bandpass filtered the result to create the 38 KHz. I would call that doubling.

True, but pilot phase in that topology was a cruel master. Probably why PLL surfaced as soon as it was practical. I think I had a Heathkit tuner that did it the rectifier way, separation was terrible. Keeping that circuit aligned within a degree of phase is...oh you get the idea.


Yes, yes, yes. An example of this technology can be found here:Heath AR15 Full Schematic And it performed exactly as badly you said, really quite horribly especially considering the parts count.

In my case, a MC1310P PLL-based chip replaced most of it. It needed just one non-critical adjustment, when I installed it. It appears that the MC1310p came out ca. 1976.

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george84
post Nov 17 2012, 00:23
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Hi,

It uses an advance rectifying process that's why the sound is more acoustic and very crystal clear. This new technology was spread all over the world because of the cool sound that it produces. It require a lot of stuff to do this kind of thing.

Thanks
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