[Elecraft] K4 on AM

[Jim Brown]

But it's not a "rule" based on communications, which is what ham radio 
is all about. Almost 100 years ago, Bell Labs, the premier engineering 
entity on the planet, published extensive research showing that audio 
frequencies below 400 Hz contribute almost nothing to speech 
intelligibility, but can waste 2-3 dB of transmitter power. As I'm sure 
you know, losing 3 dB is equivalent to reducing the effective power of 
our rig or amp by half! 30-40 years ago, I was working with broadcasters 
using multiband processing systems.

I too am a retired professional in the field of pro audio, where I made 
my living designing high quality sound systems for public spaces. One of 
my specialties was designing systems for acoustically difficult spaces, 
and a long established "rule" for such systems was to limit audio 
response below 500 Hz. By contrast, the "rule" you cite is aimed at 
"pleasing" audio, NOT speech intelligibility.

I've always set my TXEQ for max cut of the 50, 100, and 200 Hz band, 6 
dB cut of the 400 Hz band, a few dB peak of the top two bands, then set 
COMP for indicated 10 dB gain reduction on peaks. I do lots of 
contesting and some DXing, and consistently get very good audio reports. 
Think of it this way -- improving signal to noise ratio makes audio 
easier to listen to, far more that transmitting excessive bass and 
losing that power.

73, Jim K9YC

On 3/2/2020 6:01 PM, W2xj wrote:
> There is an old rule that the product of the lowest and highest audio frequencies should be between 450,000 and 500,000 (depending on which ‘expert’ you ask).  Under that rule, a 3 KHz audio response should have a low end response of 150 Hertz for a balanced sound.