SIGNALS & NOISE (Letters to Editor) Aug. 1983

Mike Line

Dear Editor:

I would like to offer additional information to Bert Whyte's "Behind The Scenes" column in your March 1983 issue.

Bruel & Kjaer has recently introduced a completely new line of studio microphones. These microphones are a totally new design, from capsule to connector. They have no parts in common with the 4133 or any other B & K instrumentation microphone.

There are two acoustical designs available. One has characteristics very similar to the 4133. The other has a lower self-noise level because it has a slightly larger diaphragm. Both de signs are available either for standard P48 phantom powering or for use with a special power supply which results in a transformerless system.

A complete description of these new studio microphones can be obtained from B & K Instruments, Inc., 185 Forest St., Marlborough, Mass. 01752.

-John R. Bareham, Applications Engineer, Bruel & Kjaer Instruments, Marlborough, Mass.

Superb station

Dear Editor:

I am writing in response to your February 1983 article, "WFMT: Satellite Superstation." I live in Snowmass Village, Colorado, a small town about eight miles away from the infamous Aspen, and receive cable TV through Canyon Cable. I am currently receiving WFMT via cable at 98.1 FM frequency. The sound is superb! In the stereo mode, which is the mode I constantly listen to WFMT, the cable quality is better than that of the local radio station, KSPN 97.7 FM. Of all the stations on the cable, WFMT is by far the best.

I was impressed with the coverage and inside story that Rich Warren and Daniel Queen presented in the article.

In short, the story and the station are nothing short of superb.

-Derrick DeCarlo Snowmass, Colo.

Gleaming Insights

Dear Editor:

"WFMT: Satellite Superstation" by Richard Warren and Daniel Queen in the February issue of Audio provided an excellent insight into the engineering considerations that have gone into building one of the world's best fine arts FM stations. There is much food for thought and also practical solutions to audio problems faced by any station attempting fine-arts programming.

We at Leaming Industries appreciate being noted as pioneers in stereo transmission by satellite. It should be noted that the original "deviation enhancement" system designed by Leaming Industries also delivered WFMT with a 68 dB signal-to-noise ratio, and did so on a completely linear (non-companded) system with both superior frequency response and lower distortion. This transmission system is still in use to transmit stereo TV audio for [cable networks] HTN Plus and Bravo!, as well as transmitting many stereo programs on thousands of miles of microwave systems, both here and in Canada.

Unfortunately, the article failed to note that Leaming Industries also manufactures a stereo processor that can receive WFMT as well as the host of new radio services that now use the Wegener sliding de-emphasis "comparison" system.

Information on stereo and monaural programs transmitted on subcarriers above video on satellite transponders is difficult to come by. We have assembled a list of these programs that may be of interest to readers of Audio.

There are new additions and changes of assignment taking place from time to time, mostly without prior announcement, so this list is based on the best information available at this time. It should also be noted that there are many subcarriers being transmitted that carry facsimile or data signals or even no signals at all, so this is not a list of all transmitted subcarriers, but only those of interest to Audio enthusiasts.

F. F. McClatchie, Marketing Agent Learning Industries Costa Mesa, Cal.

---------Channel Frequency----------

Shy on Samples

Dear Editor:

I was interested to read Leonard Feldman's test report on the new Sony compact digital disc player (Audio, November 1982) and noted his enthusiasm for the concept. There is no doubt that there is a requirement for a system to relieve us of the problems associated with record handling, dust and static pops and all the other draw backs of the present LP disc. In years to come, people will be amazed at the quality which was achieved with what in effect is a mechanically coupled system (stylus riding in a groove).

My disappointment with the new system lies, however, with the low sampling rate of 44 kHz. For speech telecommunications, the accepted sampling rate is twice that of the highest frequency, i.e., in a speech telephone channel of 200 to 3,400 Hz, the sampling rate of 8,000 Hz gives satisfactory speech reproduction. However, music is not speech.

Agreed, few people can hear as high as 20 kHz (half the compact digital disc's sampling rate), but I contend that the sound of music is also dependent upon harmonic content, transients and rise-times calling for frequency responses way above 20 kHz.

My feelings were reinforced by hearing a radio interview with a well-known conductor who said the low frequencies of the new discs are radically improved "but they still haven't got the higher frequencies right." There is no doubt the lower frequencies are considerably improved; bass drums now have a tonal quality and no longer 20 Hz or so, which can be difficult to reproduce on a master tape, can be perfectly reproduced when sampled at the 44-kHz rate, but the transient of a cymbal or the harmonics of a violin cannot be accurately reproduced by encoding the amplitude of just two or three samples of its waveform. I would like to see a sampling rate closer to 100 kHz adopted before the system becomes too standardized.

In conclusion, I would like to add how much I enjoy Audio, and have done so for many years. Keep up the good work!

-Keith L. Robinson; Mt. Royal, Quebec Canada

Editor's Note: Readers should note that the upper limit of human hearing is the upper limit, whether we are talking about primaries or harmonics. Now if Mr. Robinson is saying that digital re cording does not properly handle the range where normally only harmonics exist because of too low a sampling frequency, then he has a very strong argument, one where the jury is still out. However, the sampling frequency has been standardized, at 44.1 kHz, and it is just such standardization which allowed disc and player makers to bring the system to market.

-E.P.

(Source: Audio magazine, Aug. 1983)

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