Paul,
I've been following very closely the digital experiments at WOR. For the rest
of the folks: WOR is an AM radio station in New York. The most recent audio
samples of the WOR analog and digital signals are most interesting: by that I
mean the audio from the digital signal still leaves much to be desired. Maybe
someday it will equal the 'old-fashioned' analog sound, but it just isn't there
yet, and a comment to that effect has been made on the WOR web site by the
engineers themselves. Yet, WOR will continue to transmit digital AM and soon
everyone will be. Sometimes I think that hearing the word 'digital' gives
people a warm and cozy feeling because it's new! it's digital! and so it must
be better!
Yet, the RF pollution of the noise-like IBOC digital signal is awful. In the
next few years, all of us AM DXers are about to be greeted by a wall of
digital noise that is soon to fill the airwaves. It will mean the end of AM
Dxing as we know it. This is progress? This is better than a wide-bandwidth
analog audio signal? Yecch.
Back on the topic that started this whole thread... I've noticed that the mere
mention of 'enhanced SSB' or 'hi-fi SSB' or 'hi-fi audio' or '14.178' conjures
up in people's minds a signal that is 6 kHz wide (or more!) and, thus, poor
operating practice worthy, evidently, of action by the FCC itself to stop such
operation. This topic, suprisingly, always gets a really emotional response on
the bands, on the reflector, because for some reason, many hams begrudge the
efforts of a growing number of hams to produce good audio within the limits of
both Part 97 and good engineering practice.
One of the first and only things many people think of when they hear these
terms is ultra-wide bandwidth. They assume that all you have to do to get a
'hi-fi' signal is to use a transmitter that passes frequencies far above 3 kHz.
While this might help, it is by no means the only requirement or the only way
to get a good, clean signal on the air.
There is plenty to be done to your audio even if you stay within the 3 kHz
limit that is either spelled out or implied in Part 97.
Microphones, preamps, compressors, limiters, noise gates, parametric
equalizers, graphic equalizers, filters, de-essers, processors, and,
yes, wider bandwidth filters, are all things currently employed by the big boys
on, for example, 14.178.
I have heard remarkably good audio from guys with just 2.8 kHz wide filters in
their transmitters. I think part of this is because I sub-conciously compare
these signals to the average signal produced by a typical transceiver operated
by ham who has never verified the settings of his mic gain, equalization and
speech processor by actually listening to his own signal on a second receiver.
The typical ham signal is typically horrible. The hi-fi guys, in contrast, are
endlessly recording themselves, e-mailing the recordings to each other,
listening to themselves, and tweaking everything for the best possible signal.
Again, I must stress that there is a lot to do besides just widening your
signal and thus inflaming the sensibilities of other hams. A clean,
distortionless signal, even if it's only 3 kHz wide, sounds clean,
distortionless, and awesome.
To be fair, there are some guys who have special 5- or 6- kHz wide crystal
filters manufactured for their (SSB) radios, at great expense I
might add. In my opinion, this is borderline obsession and bending the spirit
of Part 97 beyond reason. I recently had a conversation with a major crystal
filter manufacturer who told me, "You'd be amazed at what some guys ask for."
These guys are probably a minority of 'hi-fi' buffs, however. Please feel free
to correct me if I'm wrong here.
A few years ago I installed high quality 2.8 kHz crystal filters in my radio so
I could hear what the fuss was all about and so that I could receive more
"hi-fi" audio from these guys. And since then I purchased a receiver with even
wider bandwidth. The received audio is very good on 3 kHz-wide transmitted
signals. I said this once before on one of the newsgroups and was laughed off
of the thread by folks who told me I was crazy. Well, I am a weekend musician
and frequently engineer my own recording sessions, so I am at least as
qualified as the next guy to offer a reasonable opinion on the matter.
Here's an experiment anyone can conduct at home: Next time you're on the phone
and making multiple phone calls, listen really closely to the audio quality of
the persons on the other end. Over time, you're going to hear both really
clean, crisp, noise-free signals and really crappy, mushy, and distorted
signals. How come? Isn't everybody restricted to the 3 kHz bandwidth of the
phone company? Shouldn't everyone sound equally bad? No. And the same goes for
hams.
I recently had an e-mail exchange with a nation-wide AM radio talk show host in
which he told me that he always announces when his callers are calling from a
cell phone, "To explain the lousy clarity," he told me. Even to this guy, there
is a difference. (See my comments about WOR above.)
Someone suggested listening on 14.178 kHz for a few weeks to get an idea of
what is being done in this arena. I would add that listening with a spectrum
analyzer, so that you have some hard data, is even better. That's a pretty good
suggestion and is required homework before weighing in on one side or the other
of this debate.
Regards,
Al W6LX
> -----Original Message-----
> From: Paul Christensen, Esq. [mailto:w9ac@arrl.net]
> Sent: Friday, 18 April 2003 12:16 PM
> To: geraldj@isunet.net; tentec@contesting.com; w8au@sssnet.com
> Subject: Re: [TenTec] Enhanced SSB
>
>
> > damping to let the microphone hear only the "golden tones"
> of the ham
> > transmitting. AM broadcast doesn't even allow going to 15 KHz.
>
> Prior to the implementation of NRSC mask in the early '90s,
> AM Broadcast stations had no upper limit. The NRSC mask now
> effectively
> limits the audio passband to approximately 9.5 kHz....and the
> service still sounds poor despite attempts by broadcast stations and
> receiver manufacturers to improve the quality.
>
> WOR in New York has been experimenting (yes, even
> broadcasters are allowed to experiment just like hams once
> were) with digital IBOC
> but the jury is still out on whether it can be a viable mode
> given sky wave propagation, fading, noise & interference, etc. The
> IBOC receiver goes into an analog "blend" mode when the BER
> reaches a pre-determined threshold. I haven't heard it, but
> I can only
> imagine...
>
> -Paul, W9AC
>
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