[Elecraft] [K3] K3 Audio Response - Version 3.33 Firmware

Mon Sep 21 17:14:02 EDT 2009

> Personally, I find that many modern SSB rigs do limit the 
> high frequencies too much. For me, there's a big improvement 
> in intelligibility between rolling off the highs quickly at 
> 2.5 KHz and allowing a full 2.7 to 3.0 kHz through. 3.0 kHz 
> was the "standard" communications upper frequency roll-off 
> for many years going back through the AM days, and I find 
> it's still preferable to me. A major difference today is that 
> back "then" we simply rolled off the upper frequencies with 
> the very simplest audio filtering - often just using bypass 
> capacitors in the audio stages that tended to attenuate 
> highs. The result was substantial audio energy being 
> transmitted well above 3 kHz. Nowadays we have the filters to 
> limit high frequencies much better. 

A clean "square sided" audio response that passes 150-200 Hz 
to 2800-3000 Hz (2.8 KHz bandwidth) with a "notch" between 
750 and 1100 Hz and a response that rises at 3 - 6 dB per 
octave between 1000 and 3000 Hz is a thing of joy to hear. 

Such a response is very efficient use of bandwidth, is 
easy to understand but not "harsh" and almost "natural" 
sounding.  Those who boost bass below 150-200 Hz do nothing 
but make their audio "muddy" - particularly if the bass boost 
is followed by any compression/clipping - and difficult to 
tune. 

I'd very much like to see the Elecraft equalizers modified 
to match 10 of the ISO 2/3 Octave standard (63, 100, 160, 
250, 400, 630, 1000, 1600, 2500, 4000 Hz) frequencies.  By 
having a "band" centered a 1000 Hz, it is possible to cut the 
interformat band (significantly reducing background noise 
in an area lacking any voice energy), to cut audio below 
even the most low pitched male voices (63 Hz), provide a 
smooth rising characteristic (1/1.6/2.5K) and sharply limit 
the high frequency (4K) components that cause adjacent 
channel interference without contributing to communication 
efficiency.  In addition, control over the two groups 
(100/160/250/400 and 1600/2500) provide the ability to 
"balance" the high/low formats compensating for variations 
between strong/weak voices. 

73, 

   ... Joe, W4TV 

> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net 
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Ron 
> D'Eau Claire
> Sent: Monday, September 21, 2009 3:36 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] [K3] K3 Audio Response - Version 3.33 Firmware
> 
> 
> Jim, K9YC, wrote:
> 
> Speakers with built-in amplifiers are notorious for RFI. I 
> often tour the 
> aisles at audio trade shows with a THF6A VHF/UHF talkie. In 
> ten years, I've 
> seen only one amplified loudspeaker that didn't pick up RF. 
> It cost about 
> $1,500 and was made in Europe.
> 
> -----------------------
> Ha! Bet the vendors loved your "test" ;-)
> 
> I've tried a couple of different "computer speakers" as well 
> as conventional "bookshelf" audio system speakers on my K3 
> and have found no need for using an auxiliary amplifier. The 
> K3 has plenty of audio power to drive external speakers in 
> almost any Hamshack. 
> 
> I'm currently using a pair of LabTec "computer" speakers that 
> bypass the internal amplifier by simply disconnecting the 
> wall wart that supplies the amplifier. Ignacy, you might try 
> that and see if they work  without powering the internal amp.
> 
> As Jim observes, the "ancient ones" (and most hams today) 
> don't limit their audio response out of ignorance or because 
> they couldn't. They knew that bass takes lots of power and 
> generally interferes with intelligibility, especially in us 
> guys. Not only do low frequencies hog power as Jim noted, 
> they are hardly modulated when we produce speech. Our mouths 
> and lips mostly modulate the higher harmonics, typically 
> above 300 Hz. The fundamental tone and low-order 
> power-hogging harmonics produced by our vocal cords are just 
> a "drone" with little variation other than starting and stopping. 
> 
> Personally, I find that many modern SSB rigs do limit the 
> high frequencies too much. For me, there's a big improvement 
> in intelligibility between rolling off the highs quickly at 
> 2.5 KHz and allowing a full 2.7 to 3.0 kHz through. 3.0 kHz 
> was the "standard" communications upper frequency roll-off 
> for many years going back through the AM days, and I find 
> it's still preferable to me. A major difference today is that 
> back "then" we simply rolled off the upper frequencies with 
> the very simplest audio filtering - often just using bypass 
> capacitors in the audio stages that tended to attenuate 
> highs. The result was substantial audio energy being 
> transmitted well above 3 kHz. Nowadays we have the filters to 
> limit high frequencies much better. 
> 
> I understand that there's good evidence that, when digging 
> for a signal in the noise, a lower upper-frequency limit can 
> provide better communications (provided the lows below 300 Hz 
> or so are also attenuated). It's a matter of concentrating 
> the finite amount of RF into the most effective part of the 
> audio spectrum. I find such "pinched" audio tiring to listen 
> to for any amount of time, and losing the higher frequencies 
> makes many phonemes harder to decode, perhaps because of the 
> US Army's special gift to me (tinnitus from firing too many 
> rounds from my M1 rifle parked next to my ear - our steel 
> helmets don't come with ear protectors). 
> 
> Perhaps before long we'll start to see computer generated 
> speech that is optimized for minimum bandwidth and maximum 
> intelligibility rather than continue to use our clumsy, 
> inefficient and highly variable biological speech mechanism 
> called lungs, throat and mouth ;-)
> 
> After all, we've largely dispensed with that personality in 
> CW since most Hams have dumped their mechanical keys for 
> keyers that compensate for most variations in fingers 
> movements or even to a keyboard that eliminates any chance of 
> human variability or inefficiency while "pounding brass". 
> 
> Ron AC7AC
> 
> 
> 
> 
> 
> 
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