Does AM MW/HF have a Pre/De-emphasis?
 

It is late and I have been up a little too long.
I have spent an hour wading through my reffrence books,
and the ITU web pages.

Earlier today I found a reffrence that states that the
"standard Pre/De-emphasis is 75uS", and implies that
this is also true for HF.

I thought that 75uS was for non-Dolby FM,50Us for US TV and
European FM and that MW/AM and HF/AM had no pre/de-emphasis.
Have I lost what is left of my mind?

I have been trying to decide on the best pivot point for my
tone-tilt. Craig at Kiwa used 700Hz. The best diagram I found
was from a guitar link and was designed to be used with spring
reverbs and had the pivot at 1KHz. I have been experimenting
and think I may have to have two, one for 700Hz for male voices,
and one about 1.4KHz for females.

Does anyone have and use a Kiwa MAP unit?
Is the 700Hz too low to be really efective on female voices?

Thanks
Terry

wrote in message
ups.com...
It is late and I have been up a little too long.
I have spent an hour wading through my reffrence books,
and the ITU web pages.

Earlier today I found a reffrence that states that the
"standard Pre/De-emphasis is 75uS", and implies that
this is also true for HF.

I thought that 75uS was for non-Dolby FM,50Us for US TV and
European FM and that MW/AM and HF/AM had no pre/de-emphasis.
Have I lost what is left of my mind?

It's not quite as simple as that. All broadcast audio is processed. Here's
a brief history:

http://www.bext.com/histproc.htm

Clear Channel is adopting IBOC and has developed a coincidental interest in
reducing the bandwidth of AM audio:

http://www.rwonline.com/reference-ro...andwidth.shtml


I have been trying to decide on the best pivot point for my
tone-tilt. Craig at Kiwa used 700Hz. The best diagram I found
was from a guitar link and was designed to be used with spring
reverbs and had the pivot at 1KHz. I have been experimenting
and think I may have to have two, one for 700Hz for male voices,
and one about 1.4KHz for females.

There might also be a station to station difference. Stations can process
their audio differently.

Frank Dresser

FM stations in the United Stated use a 75uS deemphasis while European FM
stations use a 50uS deemphasis. The reason for this is because the FM
transmitting stations use a preemphasis, boosting the transmitted treble
response above a certain frequency. The end result of this technique is a
better signal to noise ratio at the receiving end.
Without a deemphasis network in your FM receiver, the received audio would
sound trebly, similar to, but not exactly not like listening to a dolby
encoded tape on a non-dolby tape playback machine.
AM stations do not use any preemphasis so a deemphasis network after the
detector in your receiver is not required.
It is true that digital modes such as IBOC are being use on the MW band, but
this is a totally different technique.

Pete

"Frank Dresser" wrote in message
...

wrote in message
ups.com...
It is late and I have been up a little too long.
I have spent an hour wading through my reffrence books,
and the ITU web pages.

Earlier today I found a reffrence that states that the
"standard Pre/De-emphasis is 75uS", and implies that
this is also true for HF.

I thought that 75uS was for non-Dolby FM,50Us for US TV and
European FM and that MW/AM and HF/AM had no pre/de-emphasis.
Have I lost what is left of my mind?

It's not quite as simple as that. All broadcast audio is processed.
Here's
a brief history:

http://www.bext.com/histproc.htm

Clear Channel is adopting IBOC and has developed a coincidental interest
in
reducing the bandwidth of AM audio:

http://www.rwonline.com/reference-ro...andwidth.shtml


I have been trying to decide on the best pivot point for my
tone-tilt. Craig at Kiwa used 700Hz. The best diagram I found
was from a guitar link and was designed to be used with spring
reverbs and had the pivot at 1KHz. I have been experimenting
and think I may have to have two, one for 700Hz for male voices,
and one about 1.4KHz for females.

There might also be a station to station difference. Stations can process
their audio differently.

Frank Dresser

"Pete KE9OA" wrote in message
...

[snip]

AM stations do not use any preemphasis so a deemphasis network after the
detector in your receiver is not required.

It's my understanding that there's no FCC standard for AM stations to
preemphasize their audio, but nearly all do in order to compensate for the
normal roll off. I have an old school high fidelity AM receiver, and AM
stations usually sound rather shrill on the "Hi-Fi" IF bandwidth position.

A quick google search brings up:

"In 1977 Orban Associates introduced "Optimod-AM." This unit contained a
high-slope receiver equalizer to pre-compensate for the highly rolled-off
radios of the time, "

http://www.bext.com/histproc.htm

"and Omnia exclusives like a pre-emphasis section placed behind the
multi-band limiters to create a more consistent, natural sound."

http://www.omniaaudio.com/am.htm


It is true that digital modes such as IBOC are being use on the MW band,
but
this is a totally different technique.

Pete


I brought up IBOC because Clear Channel wants all AM radio stations to limit
their audio bandwidth to 5 - 6 kHz. One of the reasons for the change was
given:

"1. Increased modulation efficiency. By eliminating the broadcast of the
high-frequency energy, we can increase the amount of energy that is in the
20 Hz to 5 kHz region. Let's not forget that due to pre-emphasis, higher
frequencies are boosted and will have a more profound effect on total
modulation than lower frequencies will."

http://www.rwonline.com/reference-ro...andwidth.shtml

I don't know if the IBOC stations use a different preemphasis on the analog
channel than the non IBOC stations.

Frank Dresser

Frank Dresser wrote:

It's not quite as simple as that. All broadcast audio is processed.
Here's
a brief history:

http://www.bext.com/histproc.htm

Clear Channel is adopting IBOC and has developed a coincidental
interest in
reducing the bandwidth of AM audio:

http://www.rwonline.com/reference-ro...andwidth.shtml


There might also be a station to station difference. Stations can
process
their audio differently.

Frank Dresser
---------------------------------------------------
I am aware of "standard" audio processing, but the refference giving
75uS on AM through me for a minor loop. Up too long and the old brain
was a little too fogged. I tried several local AM stations with 75uS
and 50uS
and they soundeed very muffled. The exact oppositte of what I am trying
to do.

I do remember when WLW (700KHz) used to run real clasical music
programs on Sunday afternoon, and they clearly broadcast up to at least
10KHz. The cymbols were crystal clear. But that was 35~40 uears ago.

Terry

Petet thanks for jumping in. I found this refference while searching
the FCC archive. I thought it was wrong, but just wanted to verify it.

Terry

wrote in message
oups.com...

I am aware of "standard" audio processing, but the refference giving
75uS on AM through me for a minor loop. Up too long and the old brain
was a little too fogged. I tried several local AM stations with 75uS
and 50uS
and they soundeed very muffled. The exact oppositte of what I am trying
to do.


You need to have a IF about 20 kHz wide to hear the preemphasis.



I do remember when WLW (700KHz) used to run real clasical music
programs on Sunday afternoon, and they clearly broadcast up to at least
10KHz. The cymbols were crystal clear. But that was 35~40 uears ago.

Terry


No doubt. I remember the adjacent channel splatter some stations would put
out back in the late 60s and early 70s. I don't think there was a specific
FCC AM bandwidth restriction back then, the stations were just mandated to
limit interference. The FCC's minimum separation between stations in the
same market was 30 kHz, and some stations might broadcast a full 15 khz of
audio.

When the FCC reduced the channel spacing to 20 kHz in the same market they
also made a 10 kHz audio bandwidth limit official.

You could also bring this topic up in rec.radio.broadcasting. There are a
few broadcast pros there who have hands-on transmitter expirence.

Frank Dresser

wrote in message
oups.com...

I am aware of "standard" audio processing, but the refference giving
75uS on AM through me for a minor loop. Up too long and the old brain
was a little too fogged. I tried several local AM stations with 75uS
and 50uS
and they soundeed very muffled. The exact oppositte of what I am trying
to do.


Here ya go, straight from the National Radio Systems Committee:

http://www.nrscstandards.org/Standards/nrsc-1.pdf

However, in the section labeled "scope", there's a sentence which reads:

"Compliance with the standard is strictly voluntary."

Frank Dresser

Frank Dresser wrote:

Here ya go, straight from the National Radio Systems Committee:

http://www.nrscstandards.org/Standards/nrsc-1.pdf

However, in the section labeled "scope", there's a sentence which
reads:

"Compliance with the standard is strictly voluntary."

Frank Dresser
----------------------------
Thanks for the link. It is nice to find out the FCC even has errors
in their technical archive.

Terry

wrote in message
oups.com...

Thanks for the link. It is nice to find out the FCC even has errors
in their technical archive.

Terry


What was the FCC's error?

Frank Dresser

I will have to find the link, but last night I was digging around in
their
technical archives and I found a statement to the effect:"All domestic
AM BCB transmitters shall use a 75Us preemphaisis." I was looking
for the maximum analog BW a AM/MW station could use."

In the good old days class A stations could go with, I think up to
15KHz BW. I didn't feel like going to my parents and digging
through the 1955~1970 Popular Electroncs that had an article
on this issue.

I am trying to decide if I want to add a ~10KHz ceramic filter to
my outboard detector.
My fitler line up lloks like it will be:
500HZ crystal filter
2.1KHz crystal filter
3.8KHZ ceramic filter
5KHz ceramic filter
8 or 10KHz ceramic filter
(15KHz crystal filter for FM only!).
The FM will be designed and added later.

The audio will have 2 tilt tone control sections,
similar but with different pivot points. The first
centered at 700, the 2nd at ~1.4KHz. I hope to
decide if I can use one fitler with an ocatave
function, or if 2 fitlers in series will be better.
I would like to keep this simple enough for
someone other then me to use.

I am leaving the original audio chain in the R2000s
intact so that at there very least my wife will able to
use the "listening post".

A friend bought some "exotic" eletronic stuff from a
local engineering firm that went out of business.
Amoung the items were several NEDSP DSP
modules. See:
http://www.bhinstrumentation.co.uk/html/nedsp1061.html
I am trying to trade him out of at least one.
They are tiny, powerfull and don't mangle the audio
"too" much.

My "simple" outboard detector is undergoing
"mission creep".

Terry

wrote in message
oups.com...
I will have to find the link, but last night I was digging around in
their
technical archives and I found a statement to the effect:"All domestic
AM BCB transmitters shall use a 75Us preemphaisis." I was looking
for the maximum analog BW a AM/MW station could use."

My information might be outdated. Subjectively, though, I think I hear
differences in different stations. I suppose other factors in the
processing might account for any differences.



In the good old days class A stations could go with, I think up to
15KHz BW. I didn't feel like going to my parents and digging
through the 1955~1970 Popular Electroncs that had an article
on this issue.

I'm almost certain that's true. Even 10 kHz of good audio isn't bad, but I
don't hear much of that nowadays.



I am trying to decide if I want to add a ~10KHz ceramic filter to
my outboard detector.

That only allows 5 kHz for normal DSB AM. Will you be limiting the wideband
demodulation to the sync detector?


[snip]

Frank Dresser

On Sun, 26 Jun 2005 18:33:04 GMT, "Frank Dresser"
wrote:

Sec. 73.44 AM transmission system emission limitations.



(a) The emissions of stations in the AM service shall be attenuated
in
accordance with the requirements specified in paragraph (b) of this
section. Emissions shall be measured using a properly operated and
suitable swept-frequency RF spectrum analyzer using a peak hold
duration of 10 minutes, no video filtering, and a 300 Hz resolution
bandwidth, except that a wider resolution bandwidth may be employed
above 11.5 kHz to detect transient emissions. Alternatively, other
specialized receivers or monitors with appropriate characteristics
may
be used to determine compliance with the provisions of this
section,
provided that any disputes over measurement accuracy are resolved
in
favor of measurements obtained by using a calibrated spectrum
analyzer
adjusted as set forth above.

(b) Emissions 10.2 kHz to 20 kHz removed from the carrier must be
attenuated at least 25 dB below the unmodulated carrier level,
emissions 20 kHz to 30 kHz removed from the carrier must be
attenuated
at least 35 dB below the unmodulated carrier level, emissions 30
kHz
to 60 kHz removed from the carrier must be attenuated at least [5 +
1
dB/kHz] below the unmodulated carrier level, and emissions between
60
kHz and 75 kHz of the carrier frequency must be attenuated at least
65
dB below the unmodulated carrier level. Emissions removed by more
than
75 kHz must be attenuated at least 43 + 10 Log (Power in watts) or
80
dB below the unmodulated carrier level, whichever is the lesser
attenuation, except for transmitters having power less than 158
watts,
where the attenuation must be at least 65 dB below carrier level.

(c) Should harmful interference be caused to the reception of other
broadcast or non-broadcast stations by out of band emissions, the
licensee may be directed to achieve a greater degree of
attentuation
than specified in paragraphs (a) and (b) of this section.

http://kauko.hallikainen.org/FCC/FccRules/2005/73/44/

Hi Frank,

I didn't realize that..........I thought that the older AM stations took
greater pains to have flatter high frequency response. I do remember
listening to stations such as WGN on my old McIntosh MR-55, and they sounded
very good. The same stations on my Dynaco AF-6 tuner in its wide bandwidth
sounded shrill, as you describe.
As far as AM receivers, they do not have a deemphasis circuit following the
detector. With FM receivers, it is a different story.
Thanks for the info!

Pete

"Frank Dresser" wrote in message
...

"Pete KE9OA" wrote in message
...

[snip]

AM stations do not use any preemphasis so a deemphasis network after the
detector in your receiver is not required.

It's my understanding that there's no FCC standard for AM stations to
preemphasize their audio, but nearly all do in order to compensate for the
normal roll off. I have an old school high fidelity AM receiver, and AM
stations usually sound rather shrill on the "Hi-Fi" IF bandwidth position.

A quick google search brings up:

"In 1977 Orban Associates introduced "Optimod-AM." This unit contained a
high-slope receiver equalizer to pre-compensate for the highly rolled-off
radios of the time, "

http://www.bext.com/histproc.htm

"and Omnia exclusives like a pre-emphasis section placed behind the
multi-band limiters to create a more consistent, natural sound."

http://www.omniaaudio.com/am.htm


It is true that digital modes such as IBOC are being use on the MW band,
but
this is a totally different technique.

Pete


I brought up IBOC because Clear Channel wants all AM radio stations to
limit
their audio bandwidth to 5 - 6 kHz. One of the reasons for the change was
given:

"1. Increased modulation efficiency. By eliminating the broadcast of the
high-frequency energy, we can increase the amount of energy that is in the
20 Hz to 5 kHz region. Let's not forget that due to pre-emphasis, higher
frequencies are boosted and will have a more profound effect on total
modulation than lower frequencies will."

http://www.rwonline.com/reference-ro...andwidth.shtml

I don't know if the IBOC stations use a different preemphasis on the
analog
channel than the non IBOC stations.

Frank Dresser

Anytime Terry!

Pete

wrote in message
oups.com...
Petet thanks for jumping in. I found this refference while searching
the FCC archive. I thought it was wrong, but just wanted to verify it.

Terry

"Pete KE9OA"
As far as AM receivers, they do not have a deemphasis circuit
following the detector. With FM receivers, it is a different story.
___________

But in effect, almost every AM receiver has de-emphasis -- it is the result
of the "haystack" amplitude response of their RF/IF circuits driving the 2nd
detector. Higher modulating frequencies are rolled off, sometimes very
severely.

The problem with trying to compensate for it at the AM tx is that the amount
needed for "flat" system response varies considerably from rx to rx, and
even with carrier frequency. Even so, many MW/SW AM stations do boost their
highs, trying to get some of it to pass through the narrowband receivers
typically in use these days.

RF

Frank Dresser wrote:

That only allows 5 kHz for normal DSB AM. Will you be limiting the
wideband
demodulation to the sync detector?

[snip]

Frank Dresser
---------------------------------------
I meant 20KHz for 10KHz recovered audio bandwidth.
I have some nice, but wide older Murata ceramics I salvaged
30 years ago from a (then) high end Kenwood tuner AM section.
I have them in a 35mm film cansiter labled 10KHZ. Sorry for
the sloppy thinking. It had a wide/HiFi positions as well as a
naorrow/distant positon. The "narrows" are like barn doors,
maybe 14~15 wide fora 6~7KHz signal, and the "wides" are
~21 wide giving just over 10KHz.

In a way it will be nice to use all this junk I have saved for the
last 3 decades.

Terry

Let's try that again.............AM receivers don't have a deemphasis
circuit. You can state that the composite response of an AM receiver implies
a deemphasis circuit, but that is not really true if you consider a
deemphasis circuit as having a standard turnover frequency and a standard
rolloff characteristic (so many dB per octave). (I do understand your point,
though).
A deemphasis circuit, as applied after the detector in FM receivers is
designed to have a specific rolloff characteristic that is the complement of
the preemphasis characteristic applied at the transmitting end.
This holds true for broadcast stations as well as land mobile equipment.
Take a look at any of the more recent stereo FM tuners/receivers and you
will see that this characteristic is determined by the external components
in the line amp of the stereo decoder chip.
A TDA1591 data sheet gives a good example of this circuit.
And you are right.....it would be very difficult to have a standard
preemphasis curve for AM stations, because there are so my receivers with
different characteristics because of different I.F. bandwidths and different
rolloff characteristics in the audio chain.

Pete

"Richard Fry" wrote in message
...
"Pete KE9OA"
As far as AM receivers, they do not have a deemphasis circuit
following the detector. With FM receivers, it is a different story.
___________

But in effect, almost every AM receiver has de-emphasis -- it is the
result of the "haystack" amplitude response of their RF/IF circuits
driving the 2nd detector. Higher modulating frequencies are rolled off,
sometimes very severely.

The problem with trying to compensate for it at the AM tx is that the
amount needed for "flat" system response varies considerably from rx to
rx, and even with carrier frequency. Even so, many MW/SW AM stations do
boost their highs, trying to get some of it to pass through the narrowband
receivers typically in use these days.

RF

"Pete KE9OA"
....it would be very difficult to have a standard preemphasis curve for AM
stations, because there are so my receivers with different characteristics
because of different I.F. bandwidths and different rolloff characteristics
in the audio chain.
______________

In the US, broadcast AM pre-emphasis is defined by a voluntary standard of
the Nat'l Radio Systems Committee. The tx audio response is a modified 75
us curve. The curve has an 8700 Hz break frequency to reduce adjacent
channel interference.

The NRSC standard expects the amplitude response of the narrow RF/IF
bandwidth of "typical" MW broadcast receivers to restore ~ flat system
response, not that a network complementary to that at the tx be added to
audio circuits following the 2nd detector. However that is not
prohibited -- it is just more expensive. Also, that approach to
implementing AM pre/de-emphasis would not be "backward compatible."

RF (retired broadcast field/systems engineer -- RCA & Harris Corp)

Visit http://rfry.org for FM transmission system papers.

In article ,
"Frank Dresser" wrote:

wrote in message
oups.com...
I will have to find the link, but last night I was digging around
in their technical archives and I found a statement to the
effect:"All domestic AM BCB transmitters shall use a 75Us
preemphaisis." I was looking for the maximum analog BW a AM/MW
station could use."

My information might be outdated. Subjectively, though, I think I
hear differences in different stations. I suppose other factors in
the processing might account for any differences.



In the good old days class A stations could go with, I think up to
15KHz BW. I didn't feel like going to my parents and digging
through the 1955~1970 Popular Electroncs that had an article on
this issue.

I'm almost certain that's true. Even 10 kHz of good audio isn't bad,
but I don't hear much of that nowadays.



I am trying to decide if I want to add a ~10KHz ceramic filter to
my outboard detector.

That only allows 5 kHz for normal DSB AM. Will you be limiting the
wideband demodulation to the sync detector?

The best sounding radio I ever had was to connect a good audio
amplifier and speakers up to a crystal radio. There were several local
stations that were very strong signal on this radio and it sounded
fantastic. Never heard anything better since. This was using a real
crystal and cat whisker not a diode in a package. Not much there to
limit the audio response except the Q response curve of the tank
circuit. No filters at all just antenna wire and ground into the tank
circuit followed by the detector and then audio amplifier with speaker.
No need for a fancy design.

--
Telamon
Ventura, California

I agree...............still, you don't see a deemphasis network actually
following the detector in AM receivers. Are there many stations actually
using the curve?

Pete

"Richard Fry" wrote in message
...
"Pete KE9OA"
....it would be very difficult to have a standard preemphasis curve for AM
stations, because there are so my receivers with different characteristics
because of different I.F. bandwidths and different rolloff characteristics
in the audio chain.
______________

In the US, broadcast AM pre-emphasis is defined by a voluntary standard of
the Nat'l Radio Systems Committee. The tx audio response is a modified 75
us curve. The curve has an 8700 Hz break frequency to reduce adjacent
channel interference.

The NRSC standard expects the amplitude response of the narrow RF/IF
bandwidth of "typical" MW broadcast receivers to restore ~ flat system
response, not that a network complementary to that at the tx be added to
audio circuits following the 2nd detector. However that is not
prohibited -- it is just more expensive. Also, that approach to
implementing AM pre/de-emphasis would not be "backward compatible."

RF (retired broadcast field/systems engineer -- RCA & Harris Corp)

Visit http://rfry.org for FM transmission system papers.

Nice website!

Pete

"Richard Fry" wrote in message
...
"Pete KE9OA"
....it would be very difficult to have a standard preemphasis curve for AM
stations, because there are so my receivers with different characteristics
because of different I.F. bandwidths and different rolloff characteristics
in the audio chain.
______________

In the US, broadcast AM pre-emphasis is defined by a voluntary standard of
the Nat'l Radio Systems Committee. The tx audio response is a modified 75
us curve. The curve has an 8700 Hz break frequency to reduce adjacent
channel interference.

The NRSC standard expects the amplitude response of the narrow RF/IF
bandwidth of "typical" MW broadcast receivers to restore ~ flat system
response, not that a network complementary to that at the tx be added to
audio circuits following the 2nd detector. However that is not
prohibited -- it is just more expensive. Also, that approach to
implementing AM pre/de-emphasis would not be "backward compatible."

RF (retired broadcast field/systems engineer -- RCA & Harris Corp)

Visit http://rfry.org for FM transmission system papers.

"Pete KE9OA"
Are there many stations actually using the curve?

Probably at least 1/2 of them are (there's no official record that I know
of).

Nice website!

Thanks.

RF

Pete KE9OA wrote:

FM stations in the United Stated use a 75uS deemphasis while European FM
stations use a 50uS deemphasis. The reason for this is because the FM
transmitting stations use a preemphasis, boosting the transmitted treble
response above a certain frequency. The end result of this technique is a
better signal to noise ratio at the receiving end.
Without a deemphasis network in your FM receiver, the received audio would
sound trebly, similar to, but not exactly not like listening to a dolby
encoded tape on a non-dolby tape playback machine.
AM stations do not use any preemphasis so a deemphasis network after the
detector in your receiver is not required.


Actually, since NRSC II, yes they do. Part of this was to
accomodate AM stereo and make the audio competitive with FM on
receivers with sufficiently narrow IF bandwidth to accomodate
largely interference free reception. NRSC II also brickwalled audio
below 10K, so preemphasis helped overcome the top end losses from
shoddily designed IF strips.

On a vintage wideband receiver, NRSC II sounds unusually bright.
And on an NRSC II receiver the audio quality isn't really what
anyone would call high fidelity. Or even medium fidelity. It was a
feel good response to cutting the nuts off AM's potential for decent
audio in order to accomodate interference free listening as
nighttime powers were increased for local AM's.

Neither the AM stereo nor the better receiver audio developed as
expected. Tell me you're surprised. With the exception of some
dedicated receiver manufacturers focussing on AM audio quality, like
Fanfare, or builders who produced the limited number of AMAX
certifed receivers, most AM manufacturers took NRSC II as a license
to build cheaper receivers letting the preemphasis at the
transmitter compensate for poorer circuit designs.








It is true that digital modes such as IBOC are being use on the MW band, but
this is a totally different technique.

Pete

"Frank Dresser" wrote in message
...

wrote in message
roups.com...

It is late and I have been up a little too long.
I have spent an hour wading through my reffrence books,
and the ITU web pages.

Earlier today I found a reffrence that states that the
"standard Pre/De-emphasis is 75uS", and implies that
this is also true for HF.

I thought that 75uS was for non-Dolby FM,50Us for US TV and
European FM and that MW/AM and HF/AM had no pre/de-emphasis.
Have I lost what is left of my mind?

It's not quite as simple as that. All broadcast audio is processed.
Here's
a brief history:

http://www.bext.com/histproc.htm

Clear Channel is adopting IBOC and has developed a coincidental interest
in
reducing the bandwidth of AM audio:

http://www.rwonline.com/reference-ro...andwidth.shtml


I have been trying to decide on the best pivot point for my
tone-tilt. Craig at Kiwa used 700Hz. The best diagram I found
was from a guitar link and was designed to be used with spring
reverbs and had the pivot at 1KHz. I have been experimenting
and think I may have to have two, one for 700Hz for male voices,
and one about 1.4KHz for females.

There might also be a station to station difference. Stations can process
their audio differently.

Frank Dresser