Besides considering how nice it sounds we need to be considering how wide our signals are on the band.Rielly (sp) of FCC fame has warned the ham community about being careful with the width of our signals when we are trying to transmit "Hifi" sounding transmissions.Plus it's just the neighborly thing to try not to interfere with others.
73 Doug K3DUG K3 #???? -------------- Original message ---------------------- From: "Paul Christensen" <[EMAIL PROTECTED]> > > Billions of people are quite happy with the 300kHz cutoff used by the > > public telephone system (a total of 3.1kHz between 300 and 3.4kHz). > > Presumably, you mean 300 Hz, and not 300 kHz. > > > The critical frequency for speech communications is the lowest formant > > frequency; it is the resonances in the vocal cavity that convey speech, > > not the fundamental. > > You're referring to audio passband in which minimum bandwidth is used as a > function of maximum articulation. Bell Labs and other acoustical > researchers in the late 19th and early 20th centuries found that reasonable > bandwidth for voice communication was in the area you describe. The concept > was further carried on with the advent of HF SSB transmissions in the late > '40s, although AT&T Long Lines was already economizing SSB bandwidth well > before then. > > As a practical matter, analog circuits in which crystal filters are used > during SSB generation (e.g., Collins) precluded audio transmission below 300 > Hz. But we're not talking about land-line voice circuits here and > technology has marched-on well past the usage of SSB-generation techniques > that rely on crystal filtering for economy. Through DSP, we easily have the > ability to extend low frequency content down well below 300 Hz and a > significant list of other tranceiver manufacturers are accommodating this > demand in the amateur radio community. > > > The lowest formant in normal speech (formant 1 for "u") spans about 200 to > > 400Hz, so 250Hz probably is a reasonable compromise; it will include the > > peak and only slightly distort the lower edge. > > It may be a compromise, but a considerable amount of voice detail occurs > below 250 Hz, even though it offer little or nothing to intelligibility and > articulation. Using a microphone, a sound card, and FFT software (e.g., > SpectraPlus) observe the extent of low frequency content of you own voice. > If you believe that relevant energy is limited to 250 Hz, you need to > research this in better detail. We already have reasonably good > articulation in the bandwidth between 300 Hz and ~ 2.8 kHz but little added > bandwidth is required to add nearly two acoustical octaves to the listening > experience. > > Incidentally, an argument can be made that to maximize intelligibility, the > upper passband should actually be closer to 3.5 kHz or even 4.0 kHz (see a > graph of the now-classic Fletcher-Munson family of loudness curves and > re-determined in later years by modern researchers). Beyond that limit, > diminishing returns on intelligibility occur. The reason the ear is most > sensitive in this area is that the ear canal forms a closed pipe against the > tympanic membrane. The resulting fundamental frequency and harmonics can > then be calculated with precision by the width of the ear canal and its > length. Of further interest is that maximum energy in the human voice is > also matched-up against the curves. So, either millions of years of > evolution or God made this association possible. Take your pick. > > The key point is that compromises must be made againt the current > state-of-the-art. It is my belief that the benefit of adding a Rx/Tx range > down to ~ 70 Hz greatly outweighs the relatively little extra bandwidth > needed (less than 200 Hz of B/W) to make a profound difference in the > listening experience. > > Paul, W9AC > > _______________________________________________ > Elecraft mailing list > Post to: Elecraft@mailman.qth.net > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
