Friday, December 09, 2005
AM RADIO CUTS ALREADY POOR FIDELITY IN HALF!
Dear Radio World Editor,
I strongly disagree with the conclusions drawn in the article "5 kHz Bandwidth Restriction suits AM" by George W. Woodard, PE, Dec. 7, 2005 Radio World.
This article not posted to web-No link yet available.
The conclusions he reached are not supported by his own data, and is contrary to the bulk of over 100 years of acoustic, medical, and electronic research.
His data and text show a -16 dB loss on his "Best" tested radio. At about 9000 Hz (NRSC-1 and 2 dictate high frequency pre-emphasis and a 10, 000 Hz cutoff) for broadcast AM. When the preemphasis that he mentions is included, this is reduced to about -6dB. NOT BAD! I'll settle for that.
Then he proposes that broadcast AM would sound better and more intelligible if the fidelity were cut in half to 5 kHz. Perhaps on short wave communication where sky wave with selective fading and selective sideband cancellation occur this might be an advantage. In AM broadcast where the primary coverage is ground wave, such effects are minimal.
Almost all acoustic, medical, electronic, speech, and other research strongly show higher fidelity, greater signal to noise, lower distortion, improve natural sound and intelligibility. The research for this is compellingly conclusive. If you have any doubt, study the research or ask any competent audiologist, medical doctor, acoustic engineer, or other professional.
The link below is to a recent white paper showing that speech intelligibility is increased with better response up to 14 kHz and there is a very significant loss of intelligibility when frequencies between 5 and 9 kHz are missing. (See Figure 2).
Add to this the very loud hiss created by HD radio-IBOC-iBiquity and AM radio is destroying itself. The level of the IBOC hiss belies it's actual loudness and loss of intelligibility because of the nature of the digital waveform vs. analog waveform. Square waves are much louder then sine waves of the same level. In addition, with most common radio detectors it is almost impossible to completely tune out this annoying and distracting digital hiss.
FM IBOC takes about 5 channels and is jamming favorite nearby stations in populated metropolitan areas, where most listeners live. It does not take a genius to divide by 5 the 100 available FM channels to see that about 20 unjammed channels is about the most you can expect in congested metropolitan areas. (4 of those channels are likely to fall in the non-commercial low end of the dial leaving only about 16 commercial FM stations).
The most favorable projections only predict that perhaps 10% of listeners will purchase HD radios in the next 5 years. Can broadcasting as we know it survive with less then 10% of it's current listeners?
HD radio is an expensive, destuctive hoax.
HD RADIO=DIGITAL DISASTER!