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A Basic Question or two on CD Emphasis/Deemphasis

Started by Unknown September 16, 2004
Allan Herriman <allan.herriman.hates.spam@ctam.com.au.invalid> writes:

> On 17 Sep 2004 14:19:11 -0400, Randy Yates > <randy.yates@sonyericsson.com> wrote: > > >glen herrmannsfeldt <gah@ugcs.caltech.edu> writes: > > > >> Allan Herriman wrote: > >> > >> (I wrote) > >> >>When was it that 4X oversampling with digital filters into > >> >>14bit DAC's were claimed to be better than 1X at 16 bits? > >> >>It seems reasonable to me that an analog anti-aliasing filter > >> >>is easier to build with the higher frequency. > >> > >> > Using current technology, the 16 bit DAC gives better performance. > >> > >> > Back then, it wasn't possible to make a cost effective monotonic 16 > >> > bit DAC. 14 bits with PWM gave better linearity, but generated more > >> > noise. > >> > >> I don't remember the PWM description. I thought there was a > >> system that used a digital filter to generate a 4x data stream > >> low pass filtered somewhere between 20kHz and 22kHz. > >> As doubling the conversion rate is equivalent to an extra bit > >> of resolution, > > > >The technique you're describing Glen is plain old oversampling. > >Each doubling buys you 3 dB which is only a "half" bit of > >resolution. Thus 16X oversampling would have been required to > >get from 14 bits to 16. > > > >This technique (oversampling followed by a lowpass digital filter) > >also has the advantage of reducing the order/complexity of the > >reconstruction filter. > > > >But I'm with you - I remember no such conversion mechanism as > >the one Allan described, but I do distinctly remember the > >oversampling systems - in fact I owned one. > > This was prior to oversampling. IIRC, it was a Philips player from > about '83 or '84 (i.e. one of the very first ones). > I am unable to find a reference, however.
Not a problem, Allan. I believe you now that I know you're distinctly referring to another technique. -- Randy Yates Sony Ericsson Mobile Communications Research Triangle Park, NC, USA randy.yates@sonyericsson.com, 919-472-1124
Eric Jacobsen wrote:

>On 16 Sep 2004 12:17:18 -0400, Randy Yates ><randy.yates@sonyericsson.com> wrote: > > > >>>The audio signal being recorded tends to have less power at high >>>frequencies. >>> >>> >>Why? >> >> >This thread is hard to keep up with! > >Randy, I think this is the same reason that FM radio systems use >preemphasis/deemphasis. To keep the PLLs operating efficiently and >keep the SNR from getting really crappy at the high frequencies, >preemphasis is applied. > >
Eh? Had anyone ever built a PLL when the FM standards were being defined? :-) Certainly nobody envisaged it being practical to use one in a consumer radio back then. Regards, Steve
Steve Underwood wrote:

> Eric Jacobsen wrote: > >> On 16 Sep 2004 12:17:18 -0400, Randy Yates >> <randy.yates@sonyericsson.com> wrote: >> >> >> >>>> The audio signal being recorded tends to have less power at high >>>> frequencies. >>> >>> Why? >>> >> >> This thread is hard to keep up with! >> >> Randy, I think this is the same reason that FM radio systems use >> preemphasis/deemphasis. To keep the PLLs operating efficiently and >> keep the SNR from getting really crappy at the high frequencies, >> preemphasis is applied. >> >> > Eh? Had anyone ever built a PLL when the FM standards were being > defined? :-) Certainly nobody envisaged it being practical to use one in > a consumer radio back then. > > Regards, > Steve
Oh? There was AFC in Pre-war FM tuners when FM was where TV channel 1 would be if there were a channel 1. AFC is frequency lock. Add an integrator, and it becomes a phase lock. We knew how to integrate in 1936, but AFC didn't need it. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
Jerry Avins wrote:

> Steve Underwood wrote: > >> Eric Jacobsen wrote: >> >>> On 16 Sep 2004 12:17:18 -0400, Randy Yates >>> <randy.yates@sonyericsson.com> wrote: >>> >>> >>> >>>>> The audio signal being recorded tends to have less power at high >>>>> frequencies. >>>> >>>> >>>> Why? >>>> >>> >>> >>> This thread is hard to keep up with! >>> >>> Randy, I think this is the same reason that FM radio systems use >>> preemphasis/deemphasis. To keep the PLLs operating efficiently and >>> keep the SNR from getting really crappy at the high frequencies, >>> preemphasis is applied. >>> >>> >> Eh? Had anyone ever built a PLL when the FM standards were being >> defined? :-) Certainly nobody envisaged it being practical to use one >> in a consumer radio back then. >> >> Regards, >> Steve > > > Oh? There was AFC in Pre-war FM tuners when FM was where TV channel 1 > would be if there were a channel 1. AFC is frequency lock. Add an > integrator, and it becomes a phase lock. We knew how to integrate in > 1936, but AFC didn't need it. > > Jerry
Did you know how to integrate in 1936? I know you outdo most of us for seniority, but if you learned integration at, say, 14, that would make you...... :-) Seriously, I don't think anyone used PLLs in consumer equipment until Signetics launched the first practical single chip implementations. Their FM recovery devices, and a little later their stereo decoders, revolutionised the stability of FM receivers. That was a long time after the standards were set, though. Regards, Steve
Steve Underwood wrote:

> Jerry Avins wrote: > >> Steve Underwood wrote: >> >>> Eric Jacobsen wrote: >>> >>>> On 16 Sep 2004 12:17:18 -0400, Randy Yates >>>> <randy.yates@sonyericsson.com> wrote: >>>> >>>> >>>> >>>>>> The audio signal being recorded tends to have less power at high >>>>>> frequencies. >>>>> >>>>> >>>>> >>>>> Why? >>>>> >>>> >>>> >>>> >>>> This thread is hard to keep up with! >>>> >>>> Randy, I think this is the same reason that FM radio systems use >>>> preemphasis/deemphasis. To keep the PLLs operating efficiently and >>>> keep the SNR from getting really crappy at the high frequencies, >>>> preemphasis is applied. >>>> >>>> >>> Eh? Had anyone ever built a PLL when the FM standards were being >>> defined? :-) Certainly nobody envisaged it being practical to use one >>> in a consumer radio back then. >>> >>> Regards, >>> Steve >> >> >> >> Oh? There was AFC in Pre-war FM tuners when FM was where TV channel 1 >> would be if there were a channel 1. AFC is frequency lock. Add an >> integrator, and it becomes a phase lock. We knew how to integrate in >> 1936, but AFC didn't need it. >> >> Jerry > > > Did you know how to integrate in 1936? I know you outdo most of us for > seniority, but if you learned integration at, say, 14, that would make > you...... :-) > > Seriously, I don't think anyone used PLLs in consumer equipment until > Signetics launched the first practical single chip implementations. > Their FM recovery devices, and a little later their stereo decoders, > revolutionised the stability of FM receivers. That was a long time after > the standards were set, though. > > Regards, > Steve
Steve, I could integrate (well, understand integration in principle) at 14, but I was only four in 1936. By "we", I meant the electronic engineering community. I hear you claiming that phase-locked loops didn't exist (or at least weren't in use) until integrated circuits were commercial. Did I get that right? I remember data separators for magnetic storage drums. They had PLLs built with discrete components. Later, disks -- remember those 14" platters? -- had them too. TV synch circuits depend on phase locking. That's where I got 1936 from, but it could have been earlier. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
Regardless, I think my point wasn't dependent on the use of a PLL to
demodulate the signal (although I'm not quite sure how to demodulate
FM without one).   The idea is that if FM modulation is used and one
wishes to keep the transmitted spectrum relatively flat (which is a
good thing to do to maximize SNR in the receiver), then some sort of
pre-emphasis is needed if the input spectrum isn't flat.   I think
that'll be true for any transmissions system with linear modulation.



On Mon, 20 Sep 2004 16:34:25 +0800, Steve Underwood <steveu@dis.org>
wrote:

>Jerry Avins wrote: > >> Steve Underwood wrote: >> >>> Eric Jacobsen wrote: >>> >>>> On 16 Sep 2004 12:17:18 -0400, Randy Yates >>>> <randy.yates@sonyericsson.com> wrote: >>>> >>>> >>>> >>>>>> The audio signal being recorded tends to have less power at high >>>>>> frequencies. >>>>> >>>>> >>>>> Why? >>>>> >>>> >>>> >>>> This thread is hard to keep up with! >>>> >>>> Randy, I think this is the same reason that FM radio systems use >>>> preemphasis/deemphasis. To keep the PLLs operating efficiently and >>>> keep the SNR from getting really crappy at the high frequencies, >>>> preemphasis is applied. >>>> >>>> >>> Eh? Had anyone ever built a PLL when the FM standards were being >>> defined? :-) Certainly nobody envisaged it being practical to use one >>> in a consumer radio back then. >>> >>> Regards, >>> Steve >> >> >> Oh? There was AFC in Pre-war FM tuners when FM was where TV channel 1 >> would be if there were a channel 1. AFC is frequency lock. Add an >> integrator, and it becomes a phase lock. We knew how to integrate in >> 1936, but AFC didn't need it. >> >> Jerry > >Did you know how to integrate in 1936? I know you outdo most of us for >seniority, but if you learned integration at, say, 14, that would make >you...... :-) > >Seriously, I don't think anyone used PLLs in consumer equipment until >Signetics launched the first practical single chip implementations. >Their FM recovery devices, and a little later their stereo decoders, >revolutionised the stability of FM receivers. That was a long time after >the standards were set, though. > >Regards, >Steve
Eric Jacobsen Minister of Algorithms, Intel Corp. My opinions may not be Intel's opinions. http://www.ericjacobsen.org
Eric Jacobsen wrote:

> Regardless, I think my point wasn't dependent on the use of a PLL to > demodulate the signal (although I'm not quite sure how to demodulate > FM without one). ...
Is that limited to digital, or are analog techniques included? Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
On Mon, 20 Sep 2004 15:56:08 -0400, Jerry Avins <jya@ieee.org> wrote:

>Eric Jacobsen wrote: > >> Regardless, I think my point wasn't dependent on the use of a PLL to >> demodulate the signal (although I'm not quite sure how to demodulate >> FM without one). ... > >Is that limited to digital, or are analog techniques included? > >Jerry
Ooh! I'd be _really_ interested in alternative analog techniques! Eric Jacobsen Minister of Algorithms, Intel Corp. My opinions may not be Intel's opinions. http://www.ericjacobsen.org
"Eric Jacobsen" <eric.jacobsen@ieee.org> wrote in message
news:414f5bb8.442614203@news.west.cox.net...
> On Mon, 20 Sep 2004 15:56:08 -0400, Jerry Avins <jya@ieee.org> wrote: > > >Eric Jacobsen wrote: > > > >> Regardless, I think my point wasn't dependent on the use of a PLL to > >> demodulate the signal (although I'm not quite sure how to demodulate > >> FM without one). ... > > > >Is that limited to digital, or are analog techniques included? > > > >Jerry > > Ooh! I'd be _really_ interested in alternative analog techniques!
Well, if you have a filter that has the FM signal's frequency in its transition band, the varying frequency of the FM will produce a varying amplitude, which can then be rectified to recover the modulation on the FM signal. The quality is usually not too good, but it does work with narrow band FM. Best wishes, --Phil Martel
> > > Eric Jacobsen > Minister of Algorithms, Intel Corp. > My opinions may not be Intel's opinions. > http://www.ericjacobsen.org
Eric Jacobsen wrote:
> On Mon, 20 Sep 2004 15:56:08 -0400, Jerry Avins <jya@ieee.org> wrote: > > >>Eric Jacobsen wrote: >> >> >>>Regardless, I think my point wasn't dependent on the use of a PLL to >>>demodulate the signal (although I'm not quite sure how to demodulate >>>FM without one). ... >> >>Is that limited to digital, or are analog techniques included? >> >>Jerry > > > Ooh! I'd be _really_ interested in alternative analog techniques! > > > Eric Jacobsen > Minister of Algorithms, Intel Corp. > My opinions may not be Intel's opinions. > http://www.ericjacobsen.org
The most primitive method, suitable only for narrow-band FM, is slope detection. The signal is tuned to one side of an AM detector's response curve, and the deviation converts FM to AM. Then there's Armstrong's twin AM detectors, tuned a little further apart than the peak deviation, one giving positive output, the other, negative, and their outputs summed. The next level of sophistication is the Foster-Seely discriminator. It too uses bucking detectors, but they are driven from a special winding on the last IF transformer. The vector diagram is interesting. It provides inherent linearity, so the separate detector outputs of Armstrong's design, which need careful matching, are dispensed with. It was the first design I know of suitable for mass production without tweaking for linearity. All these detectors are sensitive to AM as well, so two stages of limiting are needed for good AM rejection. The next advance was the Seely-Avins ratio detector. (My cousin Jack Avins.) At first glance, it looks much like a discriminator, but the output is the ratio of the opposing detectors, not their sum. Its lack of response to AM made it standard in cheap sets and gave it a reputation for poor quality. Given the resources demanded by a discriminator, a ratio detector outperformed one. In good sets, it was usually used with one limiter both to provide phenomenally good AM rejection and to provide a stable operating point for the AFC circuit. See http://www.see.ed.ac.uk/~gjrp/EE3/Comms/Lecture11/sld005.htm and the few panels following Jack designed an unusual pentode detector for television sets. A high-Q tank circuit tuned to the intercarrier sound carrier at 4.5 MHz was connected to the screen grid and passively driven by it. The grid wad driven by the high-passed output of the video detector. The tank responded to the average signal frequency, like a flywheel. Given the nature of a coupled tank, it oscillated in quadrature with the unmodulated carrier. I called it a flywheel detector when I saw it. It was the detector used in a B/W set I bought in 1963, and when there was a buzz from the vertical bleeding through, I got out the schematic and studied it. When I thought I had it figure out, I cursed the cheap design that brought me the buzz, and consulted Jack to see if my understanding of the "weird" detector was adequate. He told me it was his design and continued along the lines of, "I called it a quadrature detector, and I'll have you know that it's in over 300,000 sets so far and going strong. It's not only at least a dime cheaper than what else we might have used, but the sound is better and there's only one tweak. If there's a buzz, it's not from that. Humph!" What could I say but "Oops!"? He told me where to find the buzz (the sync separator was out of alignment) and I went home and fixed it. Later, Jack headed up an IC lab that designed circuits for TV and FM. That Signetics FM chip That Steve U. cited uses some of the patents that came from that group. His first significant patent was the VTVM. He had about 55 by the time he retired. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;