PRESIDENT'S MESSAGE
November 2001

1.  Craig Anderton reviews "Izotope Vinyl", billed as the ultimate weapon against HiFi. It "vinylizes" your pristine audio through parameters for turntable rumble, electrical noise (hum), record wear, amount of dust, scratches, warping amount (including edge warps), and six choices of record player vintage from 1930s phonograph to 1980s linear-tracking turntable. Anderton notes that the scratch is the least convincing of the effects, at least at low levels, but at high levels it's fine. And it's free. www.izotope.com [EQ Jan01]

2.  Five major movie studios have anounced plans to allow computer users to download rental copies of feature films over the Internet. A spokesman said the average film is about 500 megabytes in digitized form and would take 20 to 40 minutes depending on the type of broadband (high speed) connection. Once you start watching the movie you have unlimited use for 24 hours, then it erases itself. (I guess they like the idea of eliminating the middleman. The file size is not enough for HD or even DVD quality. One wonders who would be interested). [NYTimes 17Aug].

3.  Herve Deletraz's Stereophile piece on audio cables as transmission lines (Nov 01), while being thorough and mostly accurate, is completely irrelevant to home systems. A rule of thumb is that transmission line effects become important when the distances involved are more than a quarter wavelength--in the case of of 5 kHz transmitted electrically, about 10 kilometers, not a typical system cable run. His recommendation to load outputs with 250 ohms (which is an atypically high value for coaxial cable impedance) is really pernicious--doing so will cause bass rolloff and overload distortion with just about every piece of equipment (the IHF minimum load is 10 kohms). People will hear a difference, but it is due to distortion.

He calls a 10 kHz square wave signal "audioband", saying even older people can hear it. No human being on Earth can hear a 10 kHz square wave--only its 10 kHz fundamental sine wave can be heard. A 500 Hz square wave would be a reasonable simulation of music--using 10 kHz pushes his argument further into the realm of absurdity.

His use of the term "echos" is also misleading, implying an audible delayed sound. In fact due to the Haas Effect, signals arriving less than 25 milliseconds after the original sound are heard as part of the initial signal, and not an echo. His examples show 1 microsecond delayed reflections due to 100 meter cables!

He says "what we take as being due to high-frequency attenuation [of the square wave] is, in fact, the superimposition of multiple echos...". With a typical cable capacitance of 60 pF/ft, a source impedance of 250 ohms will cause a -3 dB point of 35 kHz--which easily explains the rolloff.

Referring to [his] figure 11 he says that the resistors in each leg of a balanced system should be the same as the cable impedance, but in fact they should be 1/2 the cable impedance.

David Hadaway
President, Boston Audio Society

 

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updated 11/11/04