In this article (footnote 1), we first explain the…
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It is always a matter of great interest when a difficult question, in this case the audibility of differences between amplifiers, is put to an empirical test. When the question is tested by such intelligent, knowledgeable, and unbiased investigators as John Atkinson and Will Hammond (see the July issue of Stereophile, Vol.12 No.7, p.5, the interest is even greater. Unfortunately, when the test turns out to have been flawed by errors in design and in use of statistics, as was the case here, the disappointment is also even greater.
Our point about the proper use of chi-square is, by the way, quite well established statistically and not a matter of debate. The error made in this analysis is a very common one and is frequently singled out for discussion in statistical textbooks. For example, in his authoritative 1981 statistics text, Hays warns that "caution may be required in the application of chi-square tests to data where dependency among observations may be present, as is sometimes the case in repeated observations of the same individuals." Earlier, in his classic statistics text, McNemar (1962) pointed out that the…
Given that the results came out as they did, can we conclude that the differences between the amplifiers are not audible? That is, of course, one possible conclusion, but a null result such as this raises many questions and alternative hypotheses and is essentially uninterpretable. While a positive result points to one or to a small set of conclusions, a null result tells us very little. Anything that can mess up a study can cause a null result. It is much easier to run a flawed study than a valid one and hence very easy to get a null result. (For this reason is it virtually impossible to…
The test consisted of eight pairs of excerpts from the same pieces of music (we used a wide variety of music—send SASE c/o Stereophile and we will provide the list or any other information you may request). Of these eight, four pairs were played through the same amp and four were played through different amps. To make everything nice and symmetrical, two of the four "same" pairs used the VTLs both times and two used the Adcom; for the "different" pairs, two had the VTLs first and two had the Adcom first.
Our design was intended to cope with the problem that some musical selections might…
The packing of the room must also have reduced the audibility of the differences between the amplifiers in imaging. Standing far off-center in our listening room caused the images to compress and rendered the already subtle imaging differences between the amplifiers impossible to detect. Many of the listeners in the Stereophile study were non-optimally situated for good imaging, and the attenuation of highs probably also affected imaging by degrading important stereophonic cues in the high frequencies.
Despite our presentation of what may seem a thoroughgoing pan of the Stereophile study…
Sidebar: A Comment on the Statistics
With respect to the authors (who, of course, have probably forgotten more about statistics than I ever learned), I find their statement that the proper use of chi-square test is not a matter of debate is too strict a guideline. I strongly feel that each test should be considered independent. My co-worker Will Hammond is adamant that the randomization of our tests would have successfully counteracted any tendency for dependency among the observations to develop.
Yes, if one person takes the test seven times, he or she doesn't change attitudes…
There's a whorish aspect to reviewing that some readers and industry critics never tire of mentioning, as if they've stumbled onto some great revelation: that we writers seem to flit from new product to new product, sometimes gushing like cracked fire hydrants over one amplifier one month, only to gush over another amp the following month.
While the goal of most consumers is to find one true love of a component and stick with it for a long time, our job is to wolf-whistle or blow raspberries at the endless passing parade. It's the reviewer's job to try to remain dispassionate. However,…
I gazed admiringly at the HP-100's innards. Instead of spending the development years tacking on circuits in an effort to improve the sound, the Hovland design team clearly devoted itself to carving away superfluous clutter, just as an editor removes words to clean up copy. The layout looks so clean and simple. But, of course, looks can be deceiving. What goes on under the HP-100's hood is anything but.
Hovland says they chose a solid-state power supply for greater reliability, contending that tube rectifiers deteriorate sonically in a slow, insidious way. The HP-100's power supply doesn…
Let's Play!
Its design is "minimalist" and it lacks remote control, but otherwise the HP-100 is a full-featured preamp. There are a generous eight inputs, plus a tape loop and two sets of main outputs. The preamp includes a Mono button (a must-have for any lover of monophonic LPs), Mute, and a ±5dB switched silver-contact attenuator balance control (it's out of the circuit in its centered position). The balance control is there just to touch up the soundstage in an acoustically unbalanced room.
Its design is "minimalist" and it lacks remote control, but otherwise the HP-100 is a full-featured preamp. There are a generous eight inputs, plus a tape loop and two sets of main outputs. The preamp includes a Mono button (a must-have for any lover of monophonic LPs), Mute, and a ±5dB switched silver-contact attenuator balance control (it's out of the circuit in its centered position). The balance control is there just to touch up the soundstage in an acoustically unbalanced room.
While there are two inputs labeled "CD," Hovland suggests using the tape loop for the…
And the Hovland could rock. Its speed, transparency, bass control, and treble extension delivered electric music with satisfying realism: plenty of bite to cymbal splashes, lots of punch to electric bass. It wasn't at all polite, plummy, overripe, or soft, though the liquidity sometimes gave the sound a bit too much "finesse." Still, I never felt my fingers wandering toward the acoustic, jazz, or classical shelves because that's what sounded better through the HP-100.
What the Hovland did well—almost everything—served every kind of music equally. I pulled out stuff like Neil Young's…