ECN Forum Forums Technical Discussion Electrical Theory and Applications Off Topic - "Do U Know What I Am Describing"

Scott,
I have no idea about the tuning of a 12-string guitar, never having played guitar myself before I took up Bass.
What I would like to say is, the fact of "SSB or Single Side Band".
To have a radio signal in most cases, you require 3 things, a carrier and 2 side-bands, the side-bands being each side of the carrier.
The distance between them on the Electromagnetic Spectrum, is known as thier Bandwidth.
With AM (amplitude-modulated) signals, you have a situation where the side-bands are modulated in sympathy with the audio signal and they vary in amplitude according to the voice or input frequency.
FM or Frequency Modulation, works on a more linear situation, where the side-bands are pre-determined.
They are constant, the voice frequency is an effect of time not amplitude of the signal.
Now, to add the Single Side Band idea.
Both of these systems can be called Double Sideband, because they both have 2 sidebands.
What Single Side Band does is chop off the Carrier and the other Side Band.
You have a choice of lower or upper sideband, but the less bandwidth you have, the more power you can put into that signal.
This is also more efficient.
Incidentally to recieve SSB you need either a reciever with a BFO (Beat Frequency Oscillator) inbuilt, or you can inductively couple one to a Shortwave reciever.
Hope this helps Scott!.

[This message has been edited by Trumpy (edited 04-27-2006).]

Most of my experience is with A5C vestigial sideband transmission in TV. The visual carrier is only 1.25 MHz (+,-10KHz with licensed offset) above the bottom of the channel assignment. You have your carrier, upper sidebands and part of the lower sidebands. There is your chroma subcarrier added to you visual signal. The aural carrier is added by a separate power amplifier through a device called a notch diplexer.

The advantages of SSB and DSB are definately on the transmitting side. There is no information in the carrier so why waste the power to send it if you don't have to. The receiving side must be able to faithfully recover the carrier, to insert into a balanced demodulator, to recover the information.

In TV, we only send the max power during horizontal and vertical sync pulses. In UHF broadcasting, we use a technique called Mod Anode Pulsing to increase beam currents during sync. So our 110 KW visual output and 2 MW ERP (effective radiated power), was only a valid number during sync, and much higher than an average.

One form of DSB suppressed carrier that we all enjoy and rarely think about, is any FM stereo broadcast. In radio, a 19KHz stero pilot signal is sent to light the light, and get doubled to recover the 38KHz subcarrier, used to reconer the (L-R) stereo subchannel. In TV MTS, we use the 15.734 KHz horizontal frequency as the stereo pilot. In both TV and radio, sharp cutoff filters are used to roll off the audio below the pilot signal. Phase modulation of the stereo pilot by audio is not a good thing.

Joe

Scott,
To answer your question about the 12-string guitar.
The normal guitar is tuned in 5th's, ie from E string at the 5th fret to A string open is a fifth.
Having said that, above the G string, it reverts to 4ths for the B and E strings.
Where is Electure when you need him?.
An E string on a 12-string (the second string in the group) is an octave above the parent (lower) string.
An octave can be thought of as this, the first two notes of "Here Comes the Bride" are one octave apart.
They are eight notes apart, in the key of C.
I'm of the opinion, less strings, less confusion!.
Hope this helps mate.

More on the 12 string guitar...
Trumpy is right about the octaves, except for the high strings B and E, which are the same octave.
http://www.guitartips.addr.com/tip28.html

It's not too difficult to play it, since you play two strings at a time, versus one string on a regular guitar. It sounds sweet, like you have a chorus of notes. The best sounding 12 strings are acoustics and the jingle-jangle Rickenbackers.

It's actually surprising how many different tunings there are for guitars.
12 string tunings can be done a number of different ways.
Common are the 1st(E) and 2nd(B) (highest musically, but lowest on the guitar physically as it's played) strings matched with a string of the same diameter, tuned to the same note.

The 3rd(G)string can be matched as the 1st and 2nd string are, but alternately it can be paired with a string, usually about the same diameter as the 1st set, tuned an octave above the base note. (This then becomes the highest note played, and is the one that causes the "ringing bell" sound you'll hear on some 12 strings).

The 4th(D)and 5th(A), strings, which are wound, are paired with smaller unwound strings tuned an octave above the basic note.
The wound 6th(E) string will be paired with a wound string that's normally the same dia as the 4th string, but tuned up to an octave above the the 6th's basic note.

You don't do much string bending with a 12 string, so the strings used are usually heavier standard gauge and not lightweights. This also makes them louder, and increases the sustain of the note, as there's more mass vibrating around.
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All of these tight heavy strings put a heck of a strain on the neck of a guitar (and are murder on your fingers). Very often a 12 string will be transposed down from the key of E into another key, which takes some of the load off. The key of C is most commonly used.(In the old days of Leadbelly, they didn't have any reinforcement in the necks, and they would warp easily or even break if tuned to E).
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Once you decide to play a guitar with a slide (bottleneck), the tunings are so numerous it would take forever to explain them, so I'll just list a couple here.

Open E (E major) E - B - G#- E - B - E
Open(Dropped)D D - A - F#- D - A - D
E minor 7th D - B - G - E - B - E
Basically you just tweak the strings up or down to suit your fancy. With a 12 string this can be lotsa tweaking. Nobody says you have to follow the tradition of matching the paired strings to each other either.

10 string Pedal Steel guitar standard tunings are C6 (GECAGECAFC) and E9(F#D#G#EBG#F#EBD)___________________________________________

The heavy metal guys have a habit of tuning down their guitars a few of notes so that they can make that "my guitar is vomiting" low note sound, or using a 7 string guitar that has a string lower than the standard's 6th.

(I knew I'd goof up somewhere, hence edit)




[This message has been edited by electure (edited 07-01-2006).]

Thanks a million Scott (Electure),
for giving us that info.
That could only come from a true guitarist.
Cheers mate.

Wow, it's good to see so many people play the guitar here. :~)