SIGNALS & NOISE (Letters to Editor) (Mar. 1987)

LEDE Article Not Authorized

Dear Editor:

The two articles entitled "Build a Live End/Dead End Listening Room" in the December and January issues of Audio, authored by William R. Hoffman, constitute significant damage to the good name, trademark, and technical reputation of my client, Mr. Don Davis. Mr. Hoffman is not an accredited Live End/Dead End designer. He has no connection with either Mr. Davis, Syn-Aud-Con, or any accredited LEDE® designer.

The article describes convention al absorption techniques and mislabels them LEDE. The techniques described are not LEDE design techniques and do not meet published LEDE criteria.

In the first article, in addition to the improper use of LEDE, each caption to each illustration is incorrectly labeled. Also, the room la belled "an LEDE demonstration room" is not remotely qualified.

We believe this is a case of trademark counterfeiting.

We request that Audio publish in equally prominent editorial space a full refutation of these articles as having anything to do with legitimate LEDE design.

We wish to reiterate that these articles constitute serious damage to our client's worldwide classes on LEDE by presenting a totally false picture of the design process.

-Richard H. Montgomery Montgomery, Elsner & Pardieck Seymour, Ind.

Editor's Note:

Mr. Davis has promised a full refutation of Mr. Hoffman's article for publication in a fu ture issue.

-E.P.

Calling All Collectors

Dear Editor:

I obtained brief details about Audio from the very helpful staff of the American Embassy in London. I hope that you can find a little space within the pages of your publication to mention what we are attempting over here in Great Britain.

Sounds Collectable was started last spring. The purpose behind this quarterly magazine is to provide space for private record collectors so that they may get in touch with one another and exchange information and records for the overall enjoyment of the hobby. We are endeavoring to build "a service for collectors-by collectors." In the main, this would cover hard-to-get and deleted-from-catalog recordings, ranging from 78s to the earlier micro-grooves.

Musically, we wish to cover classical music (solo instrumental and orchestral) to, say, the Hollywood sound-stage musical. We are non-sponsored and operate only in our spare time on a nonprofit basis.

Anyone-and we do mean anyone living anywhere in the world can join in the fun. If any of your readers would like a sample copy of our somewhat primitive but (we think) friendly magazine, they only have to ask.

Russell Barnes 42 St. Leonard's Ave.

Blandford Forum Dorset DT11 7NY England

Taking Issue With Measurements

Dear Editor:

In your November 1986 issue, Len Feldman reported the results of his tests of the dbx DX3 CD player. While most of Mr. Feldman's measurements confirm our experience, two measurements, those of amplitude linearity and stereo separation, differed significantly from ours.

First, he reported that -80 dB signals were reproduced at -68.4 dB.

Our measurements indicate that -80 dB signals are reproduced at levels very near to-80 dB when the signal itself--and only the signal--is measured. However, if a broad-band measurement is made, readings from -60 to -80 dB may be obtained because of the presence of out-of-band interference at 88.2 kHz.

As Mr. Feldman noted during his square-wave tests, the DX3 uses digital filtering with two-times oversampling and a gentle, third-order analog filter (for better phase linearity). The two-times oversampling produces an inaudible 88.2-kHz component which is attenuated to below-50 dB by the analog filter. A broad-band measurement of the -80 dB signal level will pick up some of this 88.2-kHz signal and result in erroneous readings. We are certain that the DX3's linearity is much better than was apparent from Mr. Feldman's testing.

Stereo separation is also subject to misinterpretation from the same cause, and we think that this too is the reason for the differences between Mr. Feldman's measurement of 65 to 54 dB separation and ours of 90 dB. We have measured channel separation of at least 90 dB in many DX3 CD players, and we believe that the same inconsequential out-of-band frequencies pro vide the answer to the question Mr. Feldman himself raised regarding his measurements.

It is interesting to note that proper testing of digital equipment requires not only greater resolving power on the part of the test equipment, to cope with digital's wide range and flat frequency response, but also extra care in the interpretation of test results. As Mr. Feldman himself has taken pains to point out, CD players, including the DX3, produce out-of-band components that can easily interfere with measurements but do not correlate with the audible performance which might be inferred from those measurements. We are still learning the best ways to measure digital equipment.

This learning process is, after all, one of the things that keep audio (as a hobby and an industry) so interesting.

By the way, Mr. Feldman did express a desire to see dbx produce an accessory box offering compression for use with any CD player (especially for automotive use). Last June we introduced two such products for home use, the 1BX-DS and 3BX-DS, which offer compression as well as four other signal-processing circuits. Similar to that of the DX3, their compression is dbx's professional OverEasy (gradual-onset) circuit, variable from none to 2:1, with a fixed 6 dB of gain added to the lower end of the dynamic range.

This compression is very useful when making tapes for the car as well as when using Compact Discs for back ground music.

Leslie B. Tyler Vice President, Engineering dbx Newton, Mass.

(Source: Audio magazine, Mar. 1987)

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