[Elecraft] The Dreaded 400 Hz hump

[Joe Subich, W4TV]

On 2022-05-20 8:36 PM, jerry wrote:
 > I remember reading a magazine article many years ago...

QST, Dec 1977, Nov and Dec 1978 also the ARRL Handbook, 57th
Edition (1980).

> They showed a hole of frequencies in the normal human voice audio 
> spectrum where there is not much energy.  It was proposed to create
> a new modulation where the higher frequencies would be shifted down
> into the hole - thus letting the SSB signal take up less spectrum -
> and then shifting those audio frequencies back up at the receive
> end.

I think it was called NBVM (narrow band voice modulation).  Used
a hard lowpass filter around 600 Hz to preserve the low audio,
a bandpass filter to "select" 1500-2500 Hz, a balanced modullator
with a 3100 Hz "carrier" and pandpass filter to select the lower
sideband.  This resulted in the 1500 - 2500 Hz audio being inverted
into 600 Hz - 1600 Hz and the total transmitted voice bandwith of
just 1400 Hz (200-1600 Hz).


73,

    ... Joe, W4TV


On 2022-05-20 8:36 PM, jerry wrote:
> I remember reading a magazine article many years ago... They showed a 
> hole of frequencies in the normal human voice audio
> spectrum where there is not much energy.  It was proposed to create a 
> new modulation where the higher frequencies would be
> shifted down into the hole - thus letting the SSB signal take up less 
> spectrum - and then shifting those audio frequencies
> back up at the receive end.
> 
>    Thinking about it...that's the sort of thing I would have expected to 
> read in Ham Radio magazine.  I miss it.
> 
>                  - Jerry KF6VB
> 
> 
> On 2022-05-20 17:10, Walter Underwood wrote:
>> About seven years ago, there was an extended discussion on this list
>> about equalization settings for transmit. I collected all the settings
>> people used and posted about the majority contour.
>>
>> https://observer.wunderwood.org/2015/09/09/transmit-audio-and-compression-with-the-elecraft-kx3/ 
>>
>>
>> wunder
>> K6WRU
>> Walter Underwood
>> CM87wj
>> http://observer.wunderwood.org/ (my blog)
>>
>>> On May 20, 2022, at 6:07 PM, Bob McGraw <rmcgraw at benlomand.net> wrote:
>>>
>>> Oh yes it is there on many SSB signals where the OP is a male. That 
>>> is where most of the fundamental male voice energy occurs. Those 
>>> signals which look uniform across the SSB TX bandpass do sound good.
>>>
>>> I attribute this to the fact most hams will "boost this and boost 
>>> that" and never give thoughts to attenuating.  In fact the 
>>> characteristics of the EQ in the boost mode are noticeable different 
>>> than the attenuate mode.  Yes, one can hear the difference.
>>>
>>> In my world of pro audio, it is a practice to attenuate first and 
>>> then boost if absolutely necessary.   Hams just can't get over the 
>>> fact they must always have more.......boost boost boost.
>>>
>>> So if ones signal is muddy or bassy, what's to do?   Attenuate the 
>>> low end first, and rarely if ever,  boost the high end.  Of course 
>>> boosting the high end will make it brighter, but not attenuating the 
>>> low end will consume lots of unnecessary transmitter power not being 
>>> used for effective communications. 50Hz - 16dB, 100Hz -16dB, 200Hz - 
>>> 16dB, 400Hz - 9dB, 800Hz - 0dB, 1.6kHz - 0dB, 2.4kHz +0dB, 2.4kHz 
>>> +3dB, 3.2kHz + 6 dB.
>>>
>>> Works for me.
>>>
>>> 73
>>>
>>> Bob, K4TAX
>>>
>>> On 5/20/2022 4:30 PM, elecraft-request at mailman.qth.net wrote:
>>>> Message: 8
>>>> Date: Thu, 19 May 2022 02:14:10 +0000 (UTC)
>>>> From: Al Lorona<alorona at sbcglobal.net>
>>>> To: Elecraft Reflector<elecraft at mailman.qth.net>
>>>> Subject: [Elecraft] [OT] The dreaded 400 Hz hump
>>>> Message-ID:<1840135010.161126.1652926450733 at mail.yahoo.com>
>>>> Content-Type: text/plain; charset=UTF-8
>>>>
>>>> Have you studied how SSB signals look on your panadapter? I believe 
>>>> about 90% of all phone signals have a very pronounced peak at about 
>>>> 400 or 500 Hz. This peak is sometimes 10 dB (or more) higher than 
>>>> the rest of the bandwidth. This is wasted power and, to my ear, 
>>>> makes signals sound muddier.
>>>>
>>>> On the other hand, every once in a while you'll see a signal that 
>>>> has a more or less flat frequency response, without any huge peaks. 
>>>> Sometimes, a signal will actually have slightly*more*  power in the 
>>>> higher frequencies, say, 2000 Hz and higher. I've noticed that these 
>>>> signals have much more articulation and punch. But these signals are 
>>>> all too scarce.
>>>>
>>>> It's pretty well known that the aging population of hams 
>>>> collectively suffers from a high frequency hearing loss. It seems to 
>>>> me that this is even more reason to carefully shape your frequency 
>>>> response and cut the dreaded 400 Hz hump.
>>>>
>>>> R,
>>>>
>>>> Al? W6LX/4
>>>
>>> -- 
>>> IF ONE EXPECTS COMPUTERS AND TECHNOLOGY TO SOLVE THEIR PROBLEMS,
>>> ONE DOESN'T UNDERSTAND COMPUTERS AND TECHNOLOGY
>>> AND ONE DOESN'T UNDERSTAND THEIR PROBLEMS."
>>>