On Sat,12/31/2016 7:01 AM, Bill wrote:
I have always been under the impression the doubling of output power will result in a power gain of 3 db.
Right.
And, that 3 db gain is the least signal increase noticeable at the receiving point.
Wrong. As an audio professional, I had to learn a lot about human perception of sound. Here are some things I've learned, both by studying what others have learned and by my own observations.
1) If some sound is all by itself (that's all that you here, no other sounds), 1 dB is the smallest change in level that most listeners will hear.
2) If some sound is surrounded by other sounds -- a single instrument in a band or orchestra, a signal in noise, a 1 dB change can be the difference between hearing it and not hearing it. When I mixed live sound for 20-40 piece orchestras (Tony Bennett, for example), correcting a balance problem usually involved slightly moving the fader for the instrument that was too loud or not loud enough. When adjusting voice paging levels in an office building, 2-3dB was the difference between not quite loud enough to get over the air conditioner noise and being to loud. A change in the frequency response of a dB or two can be the difference between sounding "right" or not.
3) If a sound is all by itself, it takes a change in level of 6-10 dB to be perceived as "twice" (or "half" as loud. But that doesn't apply to a transmitter, because we have a volume control on our radio. :)
4) Human voice levels vary widely as we talk. Variations of 20 dB are common.
5) Voice frequencies in the range of 500 - 3,000 Hz are most critical for speech intelligibility.
In addition to running more power, we can get gain from improving our antenna system. A more efficient counterpoise/radial system for a vertical, feedline with lower loss, a more efficient antenna tuner, and the biggie, an antenna that better focuses its radiation at the elevation, and/or in the direction, that gets to the other station. We can use audio compression, and we can equalize our audio to transmit only the parts of our voice that provides the greatest speech intelligibility. Compression and EQ, if done well, can yield an effective 13 dB of gain! All of those dB add up with the power that we're running. Nearly all TV and radio broadcasting makes extensive use of dynamics processing to make their signal as loud as possible, and the most skilled use careful equalization on the microphones of talkers that matter.
73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
