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Aurial Subcarrier — Parallax Forums

Aurial Subcarrier

bambinobambino Posts: 789
edited 2008-01-06 03:01 in Propeller 1
Anyone know of some good reading on aurial sub carriers. I was looking to gain some insight on how audio is transmitted to the TV!
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Comments

  • deSilvadeSilva Posts: 2,967
    edited 2008-01-02 12:15
    Bambino,
    weirdly there seems to be neither superficial nor in-depth technical information in the web about this matter.....
    So how about to read a real book, maybe:
    www.amazon.com/Guide-Video-Technology-Eugene-Trundle/dp/0750623748/ref=sr_1_17?ie=UTF8&s=books&qid=1199275712&sr=1-17
    Sorry I have not read it myself. Never mind that it's more than 10 years old. What you want to know should be in it smile.gif

    But there are many more...

    Post Edited (deSilva) : 1/2/2008 12:48:40 PM GMT
  • bambinobambino Posts: 789
    edited 2008-01-02 12:44
    Thanks, deSilva,
    Before I do though, I'll give the library a chance. 10 years old is about inline with there other technical material, so they may have it, or most likely something close.
  • deSilvadeSilva Posts: 2,967
    edited 2008-01-02 12:47
    I nearly forgot that such institutions exist smile.gif

    Universty is best. It is hardly known that they grant you access on request, even when you are neither a student nor a teacher.
  • OzStampOzStamp Posts: 377
    edited 2008-01-02 12:59
    Hi Bambino

    Chip Gracey made reference awhile ago to some websites that he used to develop the code for all the NTSC PAL drivers etc etc
    I recall that there was info there re this exact issue.
    tried to find here on the forum but not much luck...

    ron mel oz
  • deSilvadeSilva Posts: 2,967
    edited 2008-01-02 13:20
    Most likely this link
    www.ntsc-tv.com/ntsc-main-01.htm
    Much about color but very little about audio...
  • AribaAriba Posts: 2,685
    edited 2008-01-02 18:29
    Perry has made a spin code that outputs Audio from a ADC to a TV with HF modulation:
    http://forums.parallax.com/showthread.php?p=684469

    Fortunately I have it downloaded (not found it with the Forum search) , but I don't tried it.

    Andy
  • bambinobambino Posts: 789
    edited 2008-01-02 19:12
    OzStamp,deSilva,
    Very interesting, I skimed through it, Quit a bit of history in that one!
    Yes the library is often not heard of in technical data, especially since online material is so available. But per a recent thread, data sheets are sometimes too hard to find.

    Wonder if the Dewey Decimal system could tame the internet?LOL
  • JonKoppJonKopp Posts: 12
    edited 2008-01-02 20:46
    I found a pretty good breakdown of NTSC.
    It's a three part series entitled "Understanding & Measuring Video TV-RF Signals"

    http://www.sencore.com/newsletter/Jan02/JanNews/Understanding%20and%20Measuring%20Part%20I.htm
    http://www.sencore.com/newsletter/Feb02/Understanding%20MeasuringVideoTVRFSignalsPartII.htm
    http://www.sencore.com/newsletter/Mar02/TVRFpartIII.htm
  • bambinobambino Posts: 789
    edited 2008-01-02 21:05
    JonKopp, Ariba, Many Thanks.
    Ariba, do you know where the schematic is that Perry is reffering to?
  • Fred HawkinsFred Hawkins Posts: 997
    edited 2008-01-02 22:40
    bambino, why not drop Perry an email: pjm@ridge-communications.ca

    And point him back to this thread [noparse]:)[/noparse]
  • deSilvadeSilva Posts: 2,967
    edited 2008-01-02 22:52
    That is a VERY readable and quite comprehensive introduction to analogue video by Glen Kropuenske! Thank you for the links, Jon.
    However - what I already remarked above - not really helpful for audio smile.gif
  • Fred HawkinsFred Hawkins Posts: 997
    edited 2008-01-03 00:53
    The audio is just fm radio, offset into the upper part of each channel's frequency space. As far as anyone is concerned (tv engineers etc), it's just a fm tuning problem.

    The FM modulated audio carrier is positioned 4.5 MHz above the video carrier.
  • deSilvadeSilva Posts: 2,967
    edited 2008-01-03 00:58
    Sure Fred, with a little time even I could explain that in detail.
    But bambino specifically asked for THAT.....

    Subcarrier technology is very en-vougue, but nowadays handled from the digital point of view

    ----

    But maybe Bambino just wants a receipe how to output sound to a TV set?

    Indeed I have never done that...
    data sheet said...
    The AuralSub (aural sub-carrier) field selects the source
    of the FM aural (audio) sub-carrier frequency to be
    modulated on. The source is the PLLA of one of the
    cogs, identified by AuralSub’s value. This audio must
    already be modulated onto the 4.5 MHz sub-carrier by the
    source PLLA.

    So the FRQA should be set to 4.5/16 MHz and then modulated by +/- 10 kHz lets say.
    @ 80 Mhz clock this comes around 232/80_000_000/16*(4_500_000 +/- your sound in Hz)

    Have fun!

    Post Edited (deSilva) : 1/3/2008 2:02:53 AM GMT
  • Fred HawkinsFred Hawkins Posts: 997
    edited 2008-01-03 02:15
    I suppose we ought to get good at tv. In about two years we're going to be up to our ears in freely given away analog tvs. Though I'll bet recycling enterprises will be the real competition (using the power of law) to consume them all.

    Maybe our goal ought to be to sell a propeller chip app to every ntsc tv owner in the US.

    What's the schedule for digital tv in EU-land?
  • deSilvadeSilva Posts: 2,967
    edited 2008-01-03 03:33
    I am not so well informed... But the cable TV companies will continue to provide the signals for analogue TV sets. People might invest in set-top boxes. The difference between this side of the ocean and the other may be that nearly all living room TV sets have a low cost RGB input, callled SCART for high quality image.

    The driving forces may be HDTV and the luxury of big flat screens. Don't know... There are also affordable beamers, but still to noisy for the living room, let alone the sleeping room...
  • bambinobambino Posts: 789
    edited 2008-01-03 03:44
    Indeed, I do want to impliment that in an app, but deSilva you are correct in that I wanted to get a base understanding of it for starters. I did not know there was already an app with some of the ground work already laid out(Maybe all of it , as I have not had time to run the app) And indeed it sounds like there is some wire modifacations to be made before a program can make use of it.

    The history of NTSC is certainly funny, considering that the artical is pre 9/11.
    NTSC committee One was all about the super powers of hollywood trying to capitolize on the frequencies the FCC was putting up for bid and the standard for transmission. Whether technology or corporate syndicate won that round is a flip of the coin.
    NTSC committee Two was a repeat of one over color. And everyone was waiting and waiting for NTSC three, but it was housed under another committee called 9/11(Homeland security). Which basically was a move by government to take back the analog frequencies and give them to emergency personal. (Note to self. Do not build the big broadcast antinae for my propeller. Now it's just a nuisence, after feb 2009 it will be called abstruction of emergency personnel!!!!!!!!!!!!!!)
    Uncle Sam Giveth, and Uncle Sam taketh away I guess. And an average of 4lbs of lead per box headed for are garbage dumps!
  • bambinobambino Posts: 789
    edited 2008-01-03 03:51
    deSilva, Isn't the TV drivers already driving ctra and ctrb just for the vedio we use now without audio?
    Wouldn't a third counter clobber the output?
  • Fred HawkinsFred Hawkins Posts: 997
    edited 2008-01-03 07:21
    Bambino, the prop set up is not the same as broadcast tv with multiplexed signals. The sound gets sent out to an RCA plug from a different pin. And one supposes that the audio software is separate too, in its own cog.

    (Hmm, maybe the Hydra book could be useful to you)

    Post Edited (Fred Hawkins) : 1/3/2008 7:26:08 AM GMT
  • JonKoppJonKopp Posts: 12
    edited 2008-01-03 07:55
    RF modulators are pretty cheap and they work pretty well. I guess if you wanted to build one for the sake of learning how to do it you could search for a datasheet for one or something. Are you actually trying to broadcast it or just combine audio and video to input into a tv or something?
  • deSilvadeSilva Posts: 2,967
    edited 2008-01-03 08:05
    I thpught this was clear, sorry.
    Of cozrse there is no space left over in the Video COG! That was onvious from the beginning and they choose to put the audio part -if ever - into another COG.
    This "other" COG ID is programmed in the VCFG (field AURSUB). It then DIRECTLY taps this "other" COG. Quite ingenious!

    This "other" COG has to use its own Timer A. (the PLL of which is tapped).

    This video signal is output to the fourth (eight resp.) pin of the video pin group (using a 500k resistor which is already provided on most boards, as it dubbs as seperate chroma output foe S-Video).

    It's all in the manual so far.
    What's not obvious to me ist:

    - Is the PLL tapped directly, or is the divider used? (I asume the first)
    - Is it neccessary to configure the bespoken pin also from the audio COG? (I assume not)
    - What is the CTRA timer mode to be configured in the AUDIO COG? Is is mode 1? (I don't know!)
  • bambinobambino Posts: 789
    edited 2008-01-03 12:31
    Fred, Jonkopp
    The audio Of which I speak is to be broadcast to a TV. (No wires)
    The broadcast of FM signals I'm sure is well documented, but in this case, the program would have to sync with the signals coming into the set. This would also have to be an offset of the chosen channel by 4.5Mhz.

    deSilva,
    Of course another Cog would be needed, hence the Third cog I referenced. What troubles me is probably elementery. Can counters in different Cogs drive the same pin with deterministic results? This is, my guess, where another circuit comes in. Posibly giving that third counter its own pin.

    Jonkopp,
    I have no real interest in RF Transmissions, it would be neat I guess to create a transmitter for R/C apps. I am just getting a kick out of seeing the prop Broadcast TV. So far I've managed about 50'(through walls). I was just curious what was involved in placeing an audio component with the transmission so a TV could pick it up.
  • deSilvadeSilva Posts: 2,967
    edited 2008-01-03 16:27
    (a) I THINK the video COG is in total command of that "fourth pin" - it yust "taps" the PLL of the "other" COG
    (b) So it easily can offset the 4.5 MHz to the choosen carrier
  • bambinobambino Posts: 789
    edited 2008-01-03 23:04
    In reading another thread my mind finally bent around the subject matter. I was thinking that the forth pin with the 560 ohm resistor was for the broadcast of video. But it is for the broadcast of audio. please correct me if i'm wrong
  • deSilvadeSilva Posts: 2,967
    edited 2008-01-04 01:56
    There is no "broadcast of audio", Bambino.

    The video can run in two modes:
    Baseband and broadcast. o.k.?

    Now take baseband, around 5MHz "video":
    We have an OPTION here. We can ommit the additional phase modulation of the colour sub channel to the luma signal, which gives a much clearer picture.
    But in case we will use the Chroma signal it is output at the "fourth pin".
    This can be utilized to feed S-VIDEO devices, e.g.
    On some boards the "fourth pin" is connected through a 500 Ohms resistor to the three resistors of the video DAC. Well, this does not do much harm. It might sometimes run as well as if you did not select this option at all.

    Now take broadcast: The 3 resistors of the video DAC now no longer generate slow 5 MHz but some hundred MHz. There is no use for S-Video or such. Rather we now have ANOTHER OPTION: adding the audio subcarrier by a 4.5 MHz signal generated by another COG.
    Now the integration of the "forth pin" via a 500 Ohms resistor into the Video DAC makes sense!

    So you see: Two very different options in two different modes. Not very logical, but economic.

    ---
    Edit: When you just want to broadcast audio that is very simple. Just do it in "the other COG". No need for Video at all..

    Post Edited (deSilva) : 1/4/2008 2:15:17 AM GMT
  • bambinobambino Posts: 789
    edited 2008-01-04 04:38
    Thank you deSilva,
    That should be enough to get me started
  • hippyhippy Posts: 1,981
    edited 2008-01-04 15:45
    Fred Hawkins said...
    I suppose we ought to get good at tv. In about two years we're going to be up to our ears in freely given away analog tvs.

    What's the schedule for digital tv in EU-land?

    In the UK, the schedule is to go entirely digital by the end of 2012. One small area has already changed over, the rest will convert in 2008-2012.
    deSilva said...
    I am not so well informed... But the cable TV companies will continue to provide the signals for analogue TV sets. People might invest in set-top boxes. The difference between this side of the ocean and the other may be that nearly all living room TV sets have a low cost RGB input, callled SCART for high quality image.

    My cable TV company runs both analogue and digital services, but is pushing digital by reducing the number of analogue channels to just those available over-air on terrestrial. I expect their analogue service will be removed by 2012, a commercial decision rather than anything else.

    SCART / RGB in Europe will save people from having to invest in new TV's if they do not want to and I do not believe Satellite / Digital TV would have been as popular as it has been otherwise. Opposition to going digital only would have been far greater had it necessitated people having to buy new TV's. Digital Radio take-up has suffered from that in the UK.

    There are unlikely to be a lot of TV's coming onto the market cheap because of SCART, but hand-held LCD TV with 3.5mm jack AV in may - providing people don't just throw them in the bin thinking them worthless.
  • bambinobambino Posts: 789
    edited 2008-01-04 18:08
    Thanks everyone for the support on this thread, as I stated it was enough to get me started.
    Recharging my batteries right now,but I was getting clear audio signals to the set. Just some annoying square waves at the moment, but as soon as I get an ADC wired into my breadboard I'll try out a mic with some of my Elvis impersonations. Can you spell Kareoke Machinescool.gif

    @Hippy, deSilva
    What is the push in Europe for going to digital? Is the sales pitch better quality picture, audio,·etc.
    Or a Security pitch to keep the citizens more informed in the event of an emergency?
  • deSilvadeSilva Posts: 2,967
    edited 2008-01-04 18:47
    To a certain degree people are just confused. They just do not want to participate on technical discussions. They want it:
    - large
    - flicker free
    - simple
    - good content
    Whoever can deliver that at a fair price is welcome be it digital or not. We tech freaks overestimate tech arguments...

    I bought a new printer the other day. I do this for 20 years now, each third or fourth year.. This time it was a all-in one device, an extraordinarily affordable and fine HP product.
    There was no printer in the box but 11 parts, 4 different cords, 3 CD ROMs, 1 manual, 1 quick start brochure... Well, ii's just standard, I think - so sorry to bore you...
    But it took deSila three quarters of an hour until it worked, and he had to consult the manual twice. This is unbearable, as everyone must admit.. Such products will not be a success, be it digital or not...

    Post Edited (deSilva) : 1/4/2008 6:56:34 PM GMT
  • PerryPerry Posts: 253
    edited 2008-01-04 22:18
    The best example of broadcasting audio would be Chip Gracey's VocalTract module

    PUB start(tract_ptr, pos_pin, neg_pin, fm_offset) : okay

'' Start vocal tract driver - starts a cog
'' returns false if no cog available
''
''   tract_ptr = pointer to vocal tract parameters (13 bytes)
''     pos_pin = positive delta-modulation pin (-1 to disable)
''     neg_pin = negative delta-modulation pin (pos_pin must also be enabled, -1 to disable)
''   fm_offset = offset frequency for fm aural subcarrier generation (-1 to disable, 4_500_000 for NTSC)



    Phil Pilgrim's talk demo demonstrates this quite well
    http://forums.parallax.com/showthread.php?p=613308

    The the auralcog in the video driver uses the 4th pin of the video circuit to create the 4.5Mhz FM carrier.
    Since it is resistivly tied to the video/broadcast DAC, it will get mixed in with the video carrier and appear as a 4.5 MHz subcarrier on the video broadcast.

    If your interested in the FM audio, have been looking at this link:
    web.archive.org/web/20060214011755/http://transmitters.tripod.com/stereo.htm

    I like to try stereo audio with the propeller, but since I don't have a stereo TV receiver, it's a very low priority project


    Perry
  • hippyhippy Posts: 1,981
    edited 2008-01-05 16:48
    @ bambino : What is the push in Europe for going to digital?

    Primarily, IMO, more channels in the UK. TV has traditionally been roof-top aerial only and limited to five programme channels, BBC1, BBC2, ITV, C4 and C5. The first two Public Broadcasting ( licence fee funded ), the rest Commercial ( advertising revenue funded ). Subscription cable and satellite were late-comers in the UK but now firmly established, although many people are still aerial only.

    Being able to provide HD over-air is also an issue for some people, and touted as the future. Hard disk PVR's are also a major incentive to go digital as most are digital-TV only.

    Trying to balance traditional Public Broadcasting against Commercial and Subscription services is a political and social issue in the UK, so the digital push includes "FreeView", digital using existing roof-top aerials and set-top box, free access with a single one-off purchase fee, no subscription. For that, consumers can have the same as they did but digital rather than analogue and the same programme channel revenue models remain as they were.

    The real push is, "more and better quality, for little extra cost". The general result is people saying they'd "like a slice of that", so it's really self-fulfilling momentum.
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