Mark,
I'm glad you brought up the SSTV analogy. The problem is very similar. You
have a certain amount of information to send. If you cut the frequencies in
half and keep the time the same, I don't believe things will sound very good
when you restore the proper pitch. Remember it takes twice as long to send
one cycle of a sine wave at 500 hertz as it does to send one cycle of a sine
wave at 1000 hertz. So, if you converted a 1000 hertz tone that was 1 cycle
long to 500 hertz and sent it, you could only send a half cycle in the same
time. This is a simple example but I think it shows the problem of severe
fidelity loss. I think this is one case where you get what you "pay" for.
Your example of restoring the pitches involves fancy digital algorithms to
achieve. I think this might be where transmitting voice digital audio is
heading but so far the required data rate to send a digital signal requires
much more bandwidth than the original analog audio you started with. SSB
still wins in the bandwidth verses fidelity category.
Carl Moreschi N4PY
Franklinton, NC
----- Original Message -----
From: "Mark Erbaugh" <mark@microenh.com>
To: <tentec@contesting.com>
Sent: Wednesday, April 23, 2003 1:10 AM
Subject: Re: [TenTec] Slightly OT: SSB vs AM
> Carl,
>
> Yes, with that scheme we would change bandwidth for increased time. Kind
of
> like how we can send a picture in SSTV, but it takes many seconds.
However,
> I was proposing first doubling the speed (but using some sort of magic to
> keep the pitch constant) before slowing it down. So a 5 second message
> would first be sped up to 2.5 seconds, but holding the pitch constant. The
> 2.5 second message would then be played at half speed, getting back to the
> original 5 seconds.
>
> Mark
>
> ----- Original Message -----
> From: "Carl Moreschi" <n4py@earthlink.net>
> To: <tentec@contesting.com>
> Sent: Tuesday, April 22, 2003 19:04 PM
> Subject: Re: [TenTec] Slightly OT: SSB vs AM
>
>
> > Assuming you recorded your voice message on a tape recorder and played
it
> > back at half the speed, it would take twice the time to send the
message.
> > So we would be using half the bandwidth but twice the time. So the
bands
> > would in effect be just as crowded. You could get twice as many
stations
> on
> > a particular band but everybody would need to talk twice as long. You
> would
> > not gain anything and you definitly could not talk in "real" time.
> >
> > Carl Moreschi N4PY
> > Franklinton, NC
> > ----- Original Message -----
> > From: "Mark Erbaugh" <mark@microenh.com>
> > To: <tentec@contesting.com>
> > Sent: Tuesday, April 22, 2003 8:45 PM
> > Subject: Re: [TenTec] Slightly OT: SSB vs AM
> >
> >
> > > How do the circuits they use on TV to keep the audio pitch the same
when
> > > they speed up the tape work? I know they do that so that can shorten
the
> > > program and squeeze in more commercials. I remember watching a show
once
> > and
> > > after a commercial break, they didn't reengage the circuit and
everybody
> > was
> > > Alvin the chipmunk.
> > >
> > > At any rate, suppose you played the audio twice as fast, but used a
> > similar
> > > circuit to restore the original pitch. Then you took that processed
> audio
> > > and played it at half speed, this time with no pitch correction.
> Wouldn't
> > > that compress each frequency to half it's original value?
> > >
> > >
> > > 73,
> > > Mark
> > >
> > > _______________________________________________
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> > > TenTec@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/tentec
> >
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> >
>
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