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.


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.

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. 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.




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.





--
Telamon
Ventura, California



(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 am in favor of DRM.)

craigm