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Interesting P3 Observation

Bob McGraw - K4TAX
 

With recent communications and observations with my P3, I see lots of SSB signals that contain a lot of information below 300 Hz.  Much is centered around 200 Hz or so.   The point is, the fact this consumes a lot of nonessential transmit energy by worthless signal occurring in the less than 200 Hz frequency range.

One of the fellows commented to me:   " In your second point, {Still, it is representative of the TX BW and audio response.}  it seems that the majority of SSB signals do not come anywhere close to filling their passband.  Most of the energy is crowded up against the suppressed carrier frequency [low frequency audio], which is not real effective in communications.  In the "Olden Days," we'd tailor the speech amp and "build-out" the modulation transformer to get a good AM communications response.  Today, my radio has a TX equalizer and I don't have to plug the soldering iron in."

I know Jim, K9YC, has strongly advocated attenuation the three lower bands of the TX EQ as much as -16 dB each with the 4th band attenuated -9 dB to -12 dB.     I find this to be correct and does add a lot of "cleanliness" and articulation to ones transmitted audio.  And it does not affect the natural sound of the male voice.

I have attached a P3 capture of one of the represented signals.   Note the first peak to the right of the carrier frequency is 200 Hz and is clearly the most dominant part in the audio spectrum.  The green vertical bar represents the receiver bandwidth of 2.7 kHz.

73
Bob, K4TAX


Richard Katsch
 

Hi,

There seems to have been much discussion of the best equalisation settings to maximise the effective use of the available transmission power of our radios.

Nobody has yet mentioned, or I've missed, the use of the Speech Intelligibility Index (SII) as detailed in (American National Standards Institute [ANSI] S3.5-1997, 2007). This standard shows that the majority of the intelligibility of a speech signal is contained between ~400Hz to 3kHz. Transmitting below this band basically provides no more useful intelligibility. Transmitting above the band provides a little more intelligibility.

As well, if you transmit this lower frequency signal you increase the overall loudness of the signal. Reducing this perceived loudness at the receiver by decreasing the volume leads to less energy in the useful bands. You've lost both ways. Additionally the phenomenon of "upward spread of masking" can result in higher frequency sounds being masked by lower frequency sounds. This is particularly bad for those of us with a high frequency hearing loss of some sort.

All of this experimentally derived information is well detailed out on the net and provides a scientific justification for the excellent recommendations provided here to attenuate the transmission of the lower frequency bands.

Best regards
Richard Katsch
VK2EIK

Steve
 

You are so correct.  I have attended several talks given by Bob Heil regarding the useful audio spectrum that we should use in our transmitters.  He admits that any energy below 400 Hz is just energy lost.   I have set my K3s  to attenuate the first three segments of the TX EQ as much a possible. 
I talk to many folks on SSB that show the majority of their TX energy between 0 and 1000 Hz and they sound like they are in a barrel and are difficult to understand unless the conditions are exceptional.  They say they want broadcast quality audio.  Clearly they have not idea what they sound like at the receiving end and resist any suggestions.

redarlington
 

They'll sound great with really wide receivers.  Or like you said, like they're in a barrel with a lot of RF going in places your 2.8kHz filter is not letting them  through.  And when I'm on the radio, I'm open about that wide or less. Never more.  It's wasted energy and really bad for DXing, but again, does sound great if you're wide enough for it.  Bob Heil's page has great info on how to adjust mics for punch to get the important part of the audio spectrum emphasized and the rest pushed back so the watts going out are conveying useful information.  I sound funny with the settings for a PR-4 microphone to me, but everybody else thinks the audio is great and I can be not just heard, but understood all around the globe.

-Bob N3XKB

On Wed, Mar 18, 2020 at 6:44 AM Steve <99sunset@...> wrote:
You are so correct.  I have attended several talks given by Bob Heil regarding the useful audio spectrum that we should use in our transmitters.  He admits that any energy below 400 Hz is just energy lost.   I have set my K3s  to attenuate the first three segments of the TX EQ as much a possible. 
I talk to many folks on SSB that show the majority of their TX energy between 0 and 1000 Hz and they sound like they are in a barrel and are difficult to understand unless the conditions are exceptional.  They say they want broadcast quality audio.  Clearly they have not idea what they sound like at the receiving end and resist any suggestions.

K9MA
 

Indeed, "broadcast quality" emphasizes the low frequencies. That's why it's so hard to understand speech on your car radio when it's noisy. It helps a lot to just turn down the bass.

73,
Scott K9MA


On 3/18/2020 07:44, Steve wrote:
You are so correct.  I have attended several talks given by Bob Heil regarding the useful audio spectrum that we should use in our transmitters.  He admits that any energy below 400 Hz is just energy lost.   I have set my K3s  to attenuate the first three segments of the TX EQ as much a possible. 
I talk to many folks on SSB that show the majority of their TX energy between 0 and 1000 Hz and they sound like they are in a barrel and are difficult to understand unless the conditions are exceptional.  They say they want broadcast quality audio.  Clearly they have not idea what they sound like at the receiving end and resist any suggestions.


-- 
Scott  K9MA

k9ma@...

Mel Farrer, K6KBE
 

Well, for my 2 cents worth, I like a flat response from low to high.  That is what their voice sounds .like in person.  Now for contesting, who cares.

Mel, K6KBE

Virus-free. www.avg.com


On Wed, Mar 18, 2020 at 4:09 PM K9MA <K9ma@...> wrote:
Indeed, "broadcast quality" emphasizes the low frequencies. That's why it's so hard to understand speech on your car radio when it's noisy. It helps a lot to just turn down the bass.

73,
Scott K9MA


On 3/18/2020 07:44, Steve wrote:
You are so correct.  I have attended several talks given by Bob Heil regarding the useful audio spectrum that we should use in our transmitters.  He admits that any energy below 400 Hz is just energy lost.   I have set my K3s  to attenuate the first three segments of the TX EQ as much a possible. 
I talk to many folks on SSB that show the majority of their TX energy between 0 and 1000 Hz and they sound like they are in a barrel and are difficult to understand unless the conditions are exceptional.  They say they want broadcast quality audio.  Clearly they have not idea what they sound like at the receiving end and resist any suggestions.


-- 
Scott  K9MA

k9ma@...

Chuck Miller
 

On Wed, Mar 18, 2020 at 06:09 PM, K9MA wrote:
Indeed, "broadcast quality" emphasizes the low frequencies. That's why it's so hard to understand speech on your car radio when it's noisy. It helps a lot to just turn down the bass.
 
73,
Scott K9MA
Indeed, After a song is mixed with extra bass in the studio, then has extra bass added by the station, and the bass is emphasised when rebroadcast on satellite radio, its all boom, boom, boom, and just noise. Turnig down the bass helps, but not enough to make the music enjoyable. Of course I have some high frequency hearing loss from 22 years working around jet engines (US Navy ret.). Even with hearing aids it's just noise now.

73, Chuck
N0NC

Ray Maxfield
 

I set my Bass at 0 and Increase  Gain a Step at a time to +10 db at 3000 Hz.

To compensate for Hearing Loss.    Ray

 

From: Chuck Miller
Sent: Wednesday, March 18, 2020 6:08 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] Interesting P3 Observation

 

On Wed, Mar 18, 2020 at 06:09 PM, K9MA wrote:

Indeed, "broadcast quality" emphasizes the low frequencies. That's why it's so hard to understand speech on your car radio when it's noisy. It helps a lot to just turn down the bass.

 

73,

Scott K9MA

Indeed, After a song is mixed with extra bass in the studio, then has extra bass added by the station, and the bass is emphasised when rebroadcast on satellite radio, its all boom, boom, boom, and just noise. Turnig down the bass helps, but not enough to make the music enjoyable. Of course I have some high frequency hearing loss from 22 years working around jet engines (US Navy ret.). Even with hearing aids it's just noise now.

73, Chuck
N0NC