In article , craigm
wrote:

Telamon wrote:
In article , craigm
wrote:


Tom Wells wrote:

Thank you for explaining the mysteries of modulation byproducts
and bandwidth in a way that makes the truth clear for people who
may not have had radio schooling. Instead of making it sound
harder than it really is..

The saddest part of it all is that MOST of the digihash
flamethrower noise is describing to the demodulator that no
modulation is present for most audio frequencies. Even if NO audio
is present, the IBOC signal is still 45khz wide,

The bandwidth used by IBOC is 30 kHz, not 45.



describing each and every one of the possible audio passband
frequencies as 0% modulation. Instead of just letting there BE no
modulation, they've decided it's much better to have all these
little subcarriers elaborately screaming "NO MODULATION AT
1200HZ!" "NO MODULATION AT 1201 HZ!", etc. It's like having a
thousand people in a

There is not a carrier for each discrete frequency.


room screaming about nothing. In proper engineering, like with
good manners, if you have nothing to say, you keep your mouth
shut.


You need to better understand the modulation method and how digital
decoders work.


Telamon wrote:

snip

This is a simple concept that many people don't seem to get.
Information rate directly correlates to bandwidth in this way,
higher rate and more detail means larger bandwidth. Analog or
digital is just a method of encoding information. Narrow filtered
analog is similar to low rate digital. It does not matter what
digital method you use you can't get around the fact that a
better picture or audio means you need to use more bandwidth.

Oh, but it does matter. The choice if digital modulation and
compression change things.

For a given modulation method and compression scheme, what you say
is valid. More content means more mandwidth.

However, different modulation methods and compressions schemes
result in differing bandwidth requirements for the same amount of
content.

If this isn't true, then PC modems would still be running at 1200
baud.


One reason newer PC modems have higher baud rate it that they use
more bandwidth than the old ones did.


PC modems are limited by the bandwidth of the phone line.

Well, since the phone line is the medium that the information goes
through that is true but older modems did not use all that was
available and the newer transmission schemes used more of that
available bandwidth.

I'm sorry but there is a direct correlation between bandwidth and
information that can not be changed. Compression methods are not
some kind of black magic that can stuff more information in the
same number of bits. Compression methods can cause a digitized
description of analog information to be more efficient and some
methods are better than others but that is it. An example would be
a picture of a checker board could be described with fewer bits
because there is not that much information but change that to a
wide view of scenery where every bit is more random and it can't be
compressed to any extent. Compression can not cause a better
"digital description" using the same bandwidth to occur as analog
representation of the same.

To be abundantly clear here my point is that DRM can not sound
better than analog in the same bandwidth.


There is more then one way to encode the analog world into
digital and back and some methods are more efficient then others
but there is no magic digital encoding system comprised of one or
a combination of encoding methods that will magically stuff more
information into the same bandwidth.

The DRM controversy has gone on for a long time where the claim
that DRM sounds better then analog in the same bandwidth. This is
a bunch of BS. Not only does this violate the laws of physics it
further makes less sense from the standpoint of conversion of
analog to digital at the transmit end and then digital back to
analog at the receive end. Technically changing from analog to
digital and back introduces conversion errors so DRM in the same
bandwidth has to sound worse than analog. The only way DRM can
sound better is to use more bandwidth than analog.

You are completely ingoring compression and modulation methods.


Yeah, it is not germane to what I wrote.


Yes, converting analog to digital then back to analog will degrade
the analog signal. A straight wire is always better. However AM,
radio is not a straight wire.


This is all a given.


With AM radio, an analog signal is compressed, band width limited,
converted to electromagnetic waves, mixed with any other waves on
the same frequency between transmitter and receiver, converted to
an electrical signal, passed through an IF that further bandwidth
limits the signal, and then run through a detector that usually
adds at least 1% distortion.


Now you are bring other issues into the picture. I want to ignore
these issues also.


So there are are two basic concepts for anyone reading the news
group. DRM and IBOC claims are a bunch of BS. Analog or any
digital system will sound better the more bandwidth you use.

I can compress audio to a 64 kbps data rate for an iPod. This
sounds better than _any_ AM broadcast I have ever heard. Better
signal to noise, lower distortion, better audio bandwidth and
stereo.

I've also heard FM band IBOC, and I will say that it did sound
better than the analog channel. However this may have been due to
significant amounts of signal processing at one end of the chain or
the other.


Music from an Ipod is not short wave analog or DRM.

The point of my post is to dispel the notion that DRM can sound
better in the same bandwidth space as an analog signal and the
basic theory behind the reasoning, it can not regardless of the
compression algorithms and modulation scheme.


The encoding method for iPod and DRM and both forms of AAC.

My point is that it is possible for DRM to be an improvement.

Point not taken. Sure it is possible for DRM to sound better than
analog for similar reasons analog can sound better than DRM.

The underlying concept is a higher information rate translates to a
higher quality picture or sound in real time.

Just so my point in posting originally is not lost DRM started out and
still tries to claim it is an improvement over analog. This claim of
being "better" was to use the same spectral space. This is an incorrect
notion, period. It does not matter what the modulation mode,
compression or combination of compression algorithms are used,
bandwidth determines the amount of information can be transmitted over
time. If DRM is to sound "better" then a current analog signal it must
occupy more bandwidth than the analog signal so more information can be
transmitted over time.

If the analog information you want to transmit is low detail and
quality to start out with a compression scheme can give the
"appearance" that more information is being transmitted over time but
it is not. With compression it is possible to transmit low quality at a
higher rate or say two low quality streams at the same rate but this is
not the same thing as a higher data rate being transmitted.
Digitization and compression can give you more options trading off
quality and quantity but it can not magically stuff a higher data rate
of information in the same bandwidth.

This is basic information transmission theory. Look it up.

(And no, I have no desire for IBOC on the AM broadcast band. I
think there are too many associated issues, the primary one being
the consumption of 30 kHz bandwidth. IBOC on FM may work and be
viable in the long run.


I'm not either. At the least they should split the existing band
between IBOC and better would be another band.


I am in favor of DRM.)


I'm not.

--
Telamon
Ventura, California