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A letter to the Editor pointing out the use of misleading graphs, published in Electronics Australia, February 1991, pp.4-5


In a journal as devoted to accuracy and clarity as yours, it is disappointing to see one misleading graph, let alone two. I refer to the two comparison bar graphs at the foot of page 22 of your November 1990 edition.

Clearly Kodak's new Cinema Digital Sound (CDS) offers substantial improvements over existing systems. Both graphs exaggerate this by the simple expedient of representing frequency in one and sound pressure in the other as linear scales when their effect, as perceived by humans, is logarithmic.

That is not all.

The vertical frequency scale on the first graph has equally spaced markings of 0, 10, 12, 14, 16, 18 and 20 kHz. What happened to 2, 4, 6 and 8 kHz? The 20 kHz upper limit of CDS is about two thirds of an octave above the 12.5 kHz available from 35 mm Dolby Stereo optical. A quick glance at the graph gives the impression that CDS is 2 times more extended than 35 mm. Surely the whole point of a graph is to assist in the effective digestion of figures. There is not much point in doing this if the graph misleads.

© 1990 - Stephen Dawson