11-26-2004, 10:13 PM
Cita:Jorge E., Por fin ya leiste lo que escribió PP ? Yo escribí eso antes pero obvio tu cerrazon y prejuicios seguramente te impidió leerlo.
¿ Regocijarme ? ¿ De qué ? Por favor, gente verdaderamente competente, capacitada en el campo de la escucha por sobre todo y la ingeniería, con buenos sistemas de referencia, sin trabas mentales ya lo ha hecho, gracias, pero no gracias de cuando aca eres autoridad tu para venir a arrojar luz... jeje, que comico.
Lalo, por favor no te sientas atacado. Ya mencioné que no soy nadie para decir qué escucha la gente. Hay gente que dice que escucha diferencias y hay gente que no las escucha. En esto no tiene nada que ver el equipo ni el nivel auditivo de la gente; es cuestión de simple percepción.
También señalé que cada quien gasta en lo que quiere. Algunos gastan dinerales en su auto, otros en mejoras para su casa, otros gastamos en lo relacionado con el audio, etc. Unos más, otros menos, y el nivel del gasto no siempre tiene que ver con la capacidad enonómica real de cada uno de nosotros.
El equipo que tengo representa el nivel de lo que puedo gastar y me gustaría mejorarlo. Sé en dónde puedo obtener mejoras inmediatas y en donde me costará un dineral lograr apenas pequeñas diferencias.
Lo que señalo está demostrado. La leyes físicas son simples y contundentes. Soy ingeniero y manejo con soltura las cuestiones técnicas, aunque por supuesto no soy un experto ni en acústica ni en ingeniería de audio.
Pero mis conocimientos y experiencia se han dado en un área muy cercana que tiene que ver con la ingeniería de control, donde los conceptos de electrónica analógica y digital que rigen ahí son los mismos que para el mundo del audio.
Lo que he señalado es pura física. Totalmente demostrable y medible.
Como indiqué, soy un objetivista y sé bien que el problema en este tema es que muchos conceptos en el mundo del audio representan realmente un acto de fe y de ahi que sea imposible que haya un consenso.
Por eso no hay que buscarlo. Ya bien lo mencionaron todos por acá.
Mi idea simplemente es tratar de explicar lo que se puede demostrar por medio de la física. Sé que al final el tema está sujeto a la subjetividad y aunque demuestre (como muchos otros ya han demostrado) que dos más dos son cuatro, habrá gente que diga que no son cuatro, sino tres.
Regresando al asunto de la "gente capacitada para escuchar", también está demostrado que sólo en ciertos casos las conclusiones de gente entrenada sirven como referenncia.
Por ejemplo, en el caso de las bocinas en donde cualquiera puede distinguir diferencias, resultaría interesante leer este artículo:
http://www.aes.org/journal/toc/AES-Sep2003TOC.html
Differences in Performance and Preference of Trained versus Untrained Listeners in Loudspeaker Tests: A Case Study
Sean E. Olive 806
Journal of the AES
Cita:The audio industry makes many assumptions about the appropriateness of various quality testing methods, but there have not been any significant studies to validate these assumptions. The choices are reduced to using trained listeners, who are efficient and discriminating, or untrained listeners, who are more representative of the user population. This 18-month study shows that trained listeners produce the same conclusion as 268 untrained listeners when evaluating loudspeakers.Los interesados pueden pasarme su correo elecrónico y se los envío para que no tengan que pagarlo en la AES :wink:
Actualmente, el único campo donde la opinión de gente entrenada para la escucha se utiliza como referencia contundente es en la evaluación de modos de procesamiento surround o multicanal.
Leonardo:
Muy buena referencia. Es importante que queines tengan información adicional la aporten para enriquecer el tema.
Efectivamente, el procedimiento para el DBT requiere que nadie sepa acerca del objeto de estudio. En este sentido, la prueba de Dunlavy podría considerarse no totalmente valida. Sin mebrago, en el momento que se realizó fue sumamente reveladora acerca del poderde la sugestión en nuestra percepción.
El procedimiento DBT riguroso, incluyendo el método estadístico utilizando el estimador ji cuadrada y la tabla binomial pueden consultarlo en este link: http://www.pcavtech.com/abx/abx_pub.htm
Finalmente, algunos comentarios acerca del efecto placebo:
The Placebo effect. By David Carlstrom
Cita:A placebo is an ineffective treatment given in a controlled study as a reference.
In one of the first large scale double blind tests done in medicine, the test of the Salk Polio vaccine, half the test subject children were given injections of the Salk vaccine and the other half were given sterile injectable saline, a salt solution with the same percentage of salt as normal body fluids. Because the Salk vaccine was slightly pink, the placebo saline was tinted pink. That is the placebo was a treatment that looked like the real thing, but when injected would have no effect at all. The test was evaluated by comparing the reduction in polio cases in the group receiving the Salk vaccine to the group receiving saline. What could be simpler than comparing something that might work with something that doesn't work. No one had to explain this procedure more than once to the elementary school children who were the test subjects.
But an adult may ask why use the placebo at all? If it does nothing why not just compare the test group with the historical rate of polio cases? The problem is the historical rate of polio varied a lot. No one could prove why the rate changed, but they knew it did. In some summers there were far more cases than in other years. The placebo was used so the groups of children were tested in the same season under all the same conditions. Whatever the conditions enhancing or inhibiting polio in some years were, they would at least be the same for both test groups.
Why inject the children with pink saline? Why not just make a list of the untreated children's names? This is the interesting question! In this kind of test, it has been found that both test groups do better than would be expected. This seems to be because if a doctor treats someone they tend to feel better, whether the doctor gives any medicine or not.
No one knows why this is true, although there is a lot of speculation. The point is that it does happen and to test a new drug, it has to be eliminated to be sure the test results are real.
In summary placebos are used because it is normal for people to feel better when treated by a healer whether or not the healer gives effective medicine or snake oil. This fact of feeling better when treated with or without an effective treatment is called the placebo effect. That is the placebo effect is the fact that people feel better even when given a treatment that does nothing.
No one knows why this is true, but we have proof that it happens. I emphasize this because critics often try to respond to the many theories of what might cause the placebo effect. We don't know what causes it, but we do have solid proof that it does happen.
In comparing audio components the same thing happens. A new component will usually sound different from the old component. This holds true even when the component is identical, as when a trick comparison is done of one component with itself. Here too, no one knows why it happens, but there is proof that it does.
Just as the placebo effect is removed from a drug test by a double blind procedure, we can remove it from an audio comparison by preventing the listener from knowing which component is which.
With this control, it becomes much harder for the listener to tell which component he is listening to. But if he hears a difference, we can be sure it is a real difference, not an auditory placebo effect.
Audiophiles are often shocked and offended by how much change there is in their "ability" to hear sonic differences when a comparison is done with a double blind protocol. They try to blame the slightest detail of the test equipment or procedure rather than realize that the blind test result is reliable and their previous experiences were tainted by the placebo effect.
In conclusion, in any audio comparison look out for the placebo effect. Who wants to spend money for a new component because it sounds better only to find out later that there is no difference in the sound quality? If you are buying a new audio component you want to be sure you are getting a worthwhile change not just a warm feeling from the newness of it. Of course if you like to spend money and feel good about it, you have the right to do that. The results of careful double blind comparisons are for those who want the best, but have less than infinite funds, and like to get value for their money, along with those who are interested in understanding the nature of human responses.
Discúlpenme por favor la referencia en inglés :roll:
saludos!