10 julio, 2007
Curiosidades psicoacústicas
Resulta que los que se esfuerzan en demostrar que casi todo suena igual y que muy muy poquita gente es capaz de oír algunas cosas, al final van a tener algo de razón. No en lo de que todo suena igual, sino en lo de que haya poca gente capaz de oír de cierta manera, como para apreciar esas presuntas diferencias.
Al parecer, según unos estudios de Schneider de la Universidad de Heidelberg (no son de ayer ni anteayer). Hay dos tipos de oyentes. Unos, los que llaman "analíticos" se fijan más en el componente básico de los sonidos, su frecuencia fundamental y son los que su cerebro procesa la información del contenido armónico de un sonido para llegar incluso a "inventarse" la fundamental si no está presente. Los otros, los "sintéticos" poseen un cerebro que procesa mejor el contenido armónico de un sonido y es en el que centran su atención. Lo más curioso es que según los experimentos que han hecho, la gente o cae en un grupo o cae en el otro, es decir son básicamente analíticos o básicamente sintéticos, pero muy poca gente posee un tipo de audición mixto, es decir, que pocos son capaces de distinguir lo que están oyendo y diferenciar la fundamental y los armónicos y procesarlos separadamente.
Otra curiosidad es que los analíticos (los que se fijan en la fundamental) suelen preferir música con un contenido rítmico marcado y los instrumentos que se relacionan con eso, mientras que los sintéticos prefieren música con contenido melódico y armonías complejas. Mediante estudios de actividad cerebral, se ha visto que cada grupo tiene desarrolladas áreas auditivas diferentes en el hemisferio izquierdo o el derecho.
El experimento que han diseñado para estudiar esto consiste en presentar a cada sujeto 12 pares de sonidos, de manera que el segundo sonido puede ser más grave (frecuencia más baja) o más agudo (frecuencia más alta) que el primero. He hecho el test y he oído en qué consiste el truco de los sonidos usados para la prueba. Si uno aprecia en qué consiste la "trampa" puede voluntariamente escoger ser analítico o sintético, o un término medio. Eso no creo que signifique que la prueba esté mal diseñada, sino que lo habitual debe ser que la gente no se dé cuenta exactamente cómo está hecho cada sonido que se escucha en la prueba.
A continuación pego una traducción al inglés de un texto originalmente escrito en brasileño, de Jorge Bruno Fritz Knirsch, que explica con mayor profundidad el estudio y las diferencias entre los tipos de oyentes.
We shouldn’t fight about taste? Day in, day out, millions of hi-fi fans demonstrate the opposite. The discussion about the right sound regularly results in heated emotions. For example, horn loudspeakers divide the audiophile community into two camps. One side says that horn speakers falsify the sound. The other side isn’t bothered by this at all and enthuses about the precision and speed of the reproduction. The only thing they have in common is the uncomprehending head shaking of one about the other. But why is there such a splendid fight about audio qualities? How and why do we decide whether a sound does or doesn’t please us? Is it habit? Accident? Or is there more behind it? Amazing hearing test In the basement of the Neurology Department of the Heidelberg University Clinic a big step nearer the answer has been taken. Deep under the Clinic itself, in order not to disturb the sensitive hospital equipment, Dr. Peter Schneider and his colleagues of the Biomagnetic section have only recently discovered something sensational. “People actually hear differently”, is the enthusiastic summary of physicist Schneider of his results. Together with researchers from Southampton and Liverpool, the researchers have found evidence that people perceive and process pitch quite differently – something that present expert opinion completely discounts. In another cellar room, in the AUDIO hearing room, the editorial staff sits with a very special hearing test. From the speakers are emitted sequentially short peeps and after each pair the hearers cross the appropriate square, indicating whether the following tone rises or falls. Eager scratching of pencils on the distributed questionnaire can be heard. After hardly a minute it’s over. Distinct whispers run through the seat rows. Irritated glances at the neighbour’s paper. How could the colleague have possibly crossed “descending”? That tone sequence was clearly ascending! Peter Schneider collects the questionnaires in no way astonished over the different answers to his gearing test. “You have here in the editorial staff a mixture of fundamental and overtone hearers,” he explained, “you all hear the same tone, but you don’t hear them all the same way. You don’t hear better or worse, just quite simply differently.” A suspicion… Fundamental hearers and overtone hearers, that’s the new invisible border, which divides mankind into two camps. Independently of age, gender, profession and musicality, it defines how the brain perceives the pitch of sound. Each natural sound consists of a basic frequency, the fundamental, and the multiples of this frequency, the overtones. The number and strength of these overtones, the overtone spectrum, causes the character of voices, noises and instruments. In order to determine pitch, the brain looks for the fundamental in the mixture of frequencies. Even should this frequency be missing, because it wasn’t transmitted by the loudspeaker, our hearing always produces the missing fundamental from the available overtones. At least, that’s what was thought. Until now. The suspicion that tones are perceived very subjectively, was expressed as long ago as the 19th century by German scientist Hermann von Helmholtz. He differentiated so-called “synthetic hearing” by which the overtone groups were merged to a type of sound mass, from “analytical hearing”, by which the single tones were perceived consciously. Schneider and his colleagues wanted to put things on a firm basis and developed a special tone hearing test; the fundamental was removed from complex tones whose overtones represented whole number multiples of the fundamental. There was now played a sequence of tones that in fundamental frequency and number of harmonics (the whole number multiples) differed. Some people assessed the tone succession as descending, others as ascending. 334 professional musicians, 75 amateur musicians and 54 non-musicians were tested in this manner. …is confirmed With an amazing result. The test subjects were clearly split into two groups, fundamental hearers and overtone hearers. While the fundamental hearers, as previously expected, assembled the missing fundamental frequency from the available overtones and thus determined the pitch, the brain of the overtone hearers adapted the pitch from the available overtone spectrum. The chasm thus originating between the perceived pitches can be up to 4 octaves. Thus, when you hear the B above middle C played in a string concerto, the person sitting beside you may perceive the F two-and-a-half octaves higher. “It’s as if the test subject saw a blue banana instead of a yellow one,” was how Peter Schneider explained the enormous difference. “And the statistical distribution indicates that there are more extreme fundamental hearers or overtone hearers than there are “centrist” hearers who find them in balance.” In other words, there are more people who see a blue banana rather than a yellow one – the results of the studies up to now show that the frequency of the extremes is slightly higher. It is therefore possible to imagine a world with many, many blue bananas, which should be yellow for everyone. Why should this be? It is exactly this question that is occupying the Heidelberg researchers. With the knowledge that the brain assembles the tones and therefore also the pitch in several different ways, the scientists detected an amazing connection. By means of magnetic resonance imaging, the brains of 87 test subjects were anatomically recorded, and while they were listening, their brain electrical impulses were measured using magnetoencephalography. The result is amazing. The people characterised as fundamental hearers were shown to have, in the lateral region of the Heschl Gyrus (a part of the hearing cortex), an appreciably greater volume of grey matter in the left side than in the right, the overtone hearers a correspondingly greater volume in the right. Furthermore, in the case of fundamental hearers, the left side of the Heschl Gyrus reacts more strongly and distinctively to sound than does the right side, and the other way round for the overtone hearers. In the case of professional musicians, the absolute volume of grey matter in the hearing cortex is much bigger, but the relative sizes of the grey matter in the left and right sides is that same as for non-musicians. This therefore means that, for every person, independent of age, musicality or gender, one side or the other side responds more strongly to music and tones. The other half certainly doesn’t remain inactive during hearing, but from birth one of the sides dominates our perception of sounds. And this has consequences. Left the drummer, right the singer… “Many other studies have shown that the left and right sides of the hearing cortex have different functions,” explains Peter Schneider about the function separation in the brain’s hearing centre. The left hand side is particularly sensitive to short, quick impulses, for all sounds that last no longer than 50 milliseconds. The right-hand side reacts sensitively to longer tones and is responsible for the spectral manipulation of the perceived sound. “A relationship between the different hearer types and the special characteristics of the sides is only logical”. Special characteristics – that is certainly what separates fundamental and overtone hearers. Not only are the pitches differently interpreted, but also the instructions as to how sensitively a hearer will react to any given sound appear to be stored in the two halves of the hearing cortex. Quick, short, sharp impulses and virtuoso finger exercises – the left side and the fundamental hearer respond to them. Long stately melodies and the processing of sound colours – that is balm for the right side and soothes the overtone hearer. It is therefore no accident that the choice of instrument of fundamental hearers is predominantly percussion, guitar, piano and high solo instruments such as trumpet and transverse flute. On the other hand, overtone hearers choose instruments that produce long sustained tones with characteristic sound colours or formants in the spectrum – strings, lower brass or woodwind, organ and voice. Differences are apparent in the way of playing. fundamental hearers like it rhythmic or virtuosic, overtone hearers prefer long melody bridges and are especially interested in sound colours and harmony. “Interestingly enough, the arrangement of preferred instruments according to fundamental and overtone hearers corresponds with the seating arrangement of a modern symphony orchestra,” said Schneider. It’s hardly a surprise that the difference between the hearer types occurs mainly in what is for mankind the most important frequency range, 1500Hz and below. It is only a short step from musical instruments to music. How does it work out in live music? Or in the mixing of a CD? When the recording engineer is a fundamental hearer and gives more value to rhythm than to tone colour, does the result then sound less good to overtone hearers? Do we find such recordings more or less pleasing? Do some musical styles therefore appeal more to us than others? Do overtone hearers prefer symphonic music, while fundamental hearers prefer a jazz concert? These are also burning questions among scientists. “For example, it is very interesting that some hi-fi set-ups have hardly any measurable differences, but are judged to sound very different,” says Dr.André Rupp, leader of the Biomagnetics Section, “is there perhaps a relationship?” AUDIO has also posed this burning question. Are we finally on the trail of the puzzle as to why some components, be they horn speakers or flat speakers, polarise the hi-fi world so much? Base tone hearers pay more attention to timing and precision. If these criteria are fulfilled, fundamental hearers perceive tonal colouring even if these have been neglected. Overtone hearers again are inclined to forgive weaknesses in rhythm rather than tolerate sound colouring. If a rather extreme overtone hearer encounters a speaker designed and tuned by a fundamental hearer, the verdict will hardly be good. Might it be, perhaps, that here lies the secret as to why some names on the hi-fi scene are celebrated by some and demonised by others?
Por si alguno de los lectores de este sitio prefiere leer el artículo en portugués, dejo el vínculo a la web de Knirsch
Lo que más me llama la atención de esto es que comentan que la repetición del test suele dar resultados semejantes, no parece que el entrenamiento influya y el hecho de que la mayoría se enclaven en un grupo o en otro y que solamente un porcentaje muy pequeño tengan un tipo de audición mixta. Me pregunto si hará falta ese tipo de audición para ser capaz de apreciar algunas diferencias entre aparatos de audio.
Si alguien tiene curiosidad por hacer el test, que me lo diga en los comentarios dejando un e-mail y le envío los archivos. Es que no soy capaz de recordar ahora de dónde los bajé..... cosas de la edad, supongo.
Al parecer, según unos estudios de Schneider de la Universidad de Heidelberg (no son de ayer ni anteayer). Hay dos tipos de oyentes. Unos, los que llaman "analíticos" se fijan más en el componente básico de los sonidos, su frecuencia fundamental y son los que su cerebro procesa la información del contenido armónico de un sonido para llegar incluso a "inventarse" la fundamental si no está presente. Los otros, los "sintéticos" poseen un cerebro que procesa mejor el contenido armónico de un sonido y es en el que centran su atención. Lo más curioso es que según los experimentos que han hecho, la gente o cae en un grupo o cae en el otro, es decir son básicamente analíticos o básicamente sintéticos, pero muy poca gente posee un tipo de audición mixto, es decir, que pocos son capaces de distinguir lo que están oyendo y diferenciar la fundamental y los armónicos y procesarlos separadamente.
Otra curiosidad es que los analíticos (los que se fijan en la fundamental) suelen preferir música con un contenido rítmico marcado y los instrumentos que se relacionan con eso, mientras que los sintéticos prefieren música con contenido melódico y armonías complejas. Mediante estudios de actividad cerebral, se ha visto que cada grupo tiene desarrolladas áreas auditivas diferentes en el hemisferio izquierdo o el derecho.
El experimento que han diseñado para estudiar esto consiste en presentar a cada sujeto 12 pares de sonidos, de manera que el segundo sonido puede ser más grave (frecuencia más baja) o más agudo (frecuencia más alta) que el primero. He hecho el test y he oído en qué consiste el truco de los sonidos usados para la prueba. Si uno aprecia en qué consiste la "trampa" puede voluntariamente escoger ser analítico o sintético, o un término medio. Eso no creo que signifique que la prueba esté mal diseñada, sino que lo habitual debe ser que la gente no se dé cuenta exactamente cómo está hecho cada sonido que se escucha en la prueba.
A continuación pego una traducción al inglés de un texto originalmente escrito en brasileño, de Jorge Bruno Fritz Knirsch, que explica con mayor profundidad el estudio y las diferencias entre los tipos de oyentes.
We shouldn’t fight about taste? Day in, day out, millions of hi-fi fans demonstrate the opposite. The discussion about the right sound regularly results in heated emotions. For example, horn loudspeakers divide the audiophile community into two camps. One side says that horn speakers falsify the sound. The other side isn’t bothered by this at all and enthuses about the precision and speed of the reproduction. The only thing they have in common is the uncomprehending head shaking of one about the other. But why is there such a splendid fight about audio qualities? How and why do we decide whether a sound does or doesn’t please us? Is it habit? Accident? Or is there more behind it? Amazing hearing test In the basement of the Neurology Department of the Heidelberg University Clinic a big step nearer the answer has been taken. Deep under the Clinic itself, in order not to disturb the sensitive hospital equipment, Dr. Peter Schneider and his colleagues of the Biomagnetic section have only recently discovered something sensational. “People actually hear differently”, is the enthusiastic summary of physicist Schneider of his results. Together with researchers from Southampton and Liverpool, the researchers have found evidence that people perceive and process pitch quite differently – something that present expert opinion completely discounts. In another cellar room, in the AUDIO hearing room, the editorial staff sits with a very special hearing test. From the speakers are emitted sequentially short peeps and after each pair the hearers cross the appropriate square, indicating whether the following tone rises or falls. Eager scratching of pencils on the distributed questionnaire can be heard. After hardly a minute it’s over. Distinct whispers run through the seat rows. Irritated glances at the neighbour’s paper. How could the colleague have possibly crossed “descending”? That tone sequence was clearly ascending! Peter Schneider collects the questionnaires in no way astonished over the different answers to his gearing test. “You have here in the editorial staff a mixture of fundamental and overtone hearers,” he explained, “you all hear the same tone, but you don’t hear them all the same way. You don’t hear better or worse, just quite simply differently.” A suspicion… Fundamental hearers and overtone hearers, that’s the new invisible border, which divides mankind into two camps. Independently of age, gender, profession and musicality, it defines how the brain perceives the pitch of sound. Each natural sound consists of a basic frequency, the fundamental, and the multiples of this frequency, the overtones. The number and strength of these overtones, the overtone spectrum, causes the character of voices, noises and instruments. In order to determine pitch, the brain looks for the fundamental in the mixture of frequencies. Even should this frequency be missing, because it wasn’t transmitted by the loudspeaker, our hearing always produces the missing fundamental from the available overtones. At least, that’s what was thought. Until now. The suspicion that tones are perceived very subjectively, was expressed as long ago as the 19th century by German scientist Hermann von Helmholtz. He differentiated so-called “synthetic hearing” by which the overtone groups were merged to a type of sound mass, from “analytical hearing”, by which the single tones were perceived consciously. Schneider and his colleagues wanted to put things on a firm basis and developed a special tone hearing test; the fundamental was removed from complex tones whose overtones represented whole number multiples of the fundamental. There was now played a sequence of tones that in fundamental frequency and number of harmonics (the whole number multiples) differed. Some people assessed the tone succession as descending, others as ascending. 334 professional musicians, 75 amateur musicians and 54 non-musicians were tested in this manner. …is confirmed With an amazing result. The test subjects were clearly split into two groups, fundamental hearers and overtone hearers. While the fundamental hearers, as previously expected, assembled the missing fundamental frequency from the available overtones and thus determined the pitch, the brain of the overtone hearers adapted the pitch from the available overtone spectrum. The chasm thus originating between the perceived pitches can be up to 4 octaves. Thus, when you hear the B above middle C played in a string concerto, the person sitting beside you may perceive the F two-and-a-half octaves higher. “It’s as if the test subject saw a blue banana instead of a yellow one,” was how Peter Schneider explained the enormous difference. “And the statistical distribution indicates that there are more extreme fundamental hearers or overtone hearers than there are “centrist” hearers who find them in balance.” In other words, there are more people who see a blue banana rather than a yellow one – the results of the studies up to now show that the frequency of the extremes is slightly higher. It is therefore possible to imagine a world with many, many blue bananas, which should be yellow for everyone. Why should this be? It is exactly this question that is occupying the Heidelberg researchers. With the knowledge that the brain assembles the tones and therefore also the pitch in several different ways, the scientists detected an amazing connection. By means of magnetic resonance imaging, the brains of 87 test subjects were anatomically recorded, and while they were listening, their brain electrical impulses were measured using magnetoencephalography. The result is amazing. The people characterised as fundamental hearers were shown to have, in the lateral region of the Heschl Gyrus (a part of the hearing cortex), an appreciably greater volume of grey matter in the left side than in the right, the overtone hearers a correspondingly greater volume in the right. Furthermore, in the case of fundamental hearers, the left side of the Heschl Gyrus reacts more strongly and distinctively to sound than does the right side, and the other way round for the overtone hearers. In the case of professional musicians, the absolute volume of grey matter in the hearing cortex is much bigger, but the relative sizes of the grey matter in the left and right sides is that same as for non-musicians. This therefore means that, for every person, independent of age, musicality or gender, one side or the other side responds more strongly to music and tones. The other half certainly doesn’t remain inactive during hearing, but from birth one of the sides dominates our perception of sounds. And this has consequences. Left the drummer, right the singer… “Many other studies have shown that the left and right sides of the hearing cortex have different functions,” explains Peter Schneider about the function separation in the brain’s hearing centre. The left hand side is particularly sensitive to short, quick impulses, for all sounds that last no longer than 50 milliseconds. The right-hand side reacts sensitively to longer tones and is responsible for the spectral manipulation of the perceived sound. “A relationship between the different hearer types and the special characteristics of the sides is only logical”. Special characteristics – that is certainly what separates fundamental and overtone hearers. Not only are the pitches differently interpreted, but also the instructions as to how sensitively a hearer will react to any given sound appear to be stored in the two halves of the hearing cortex. Quick, short, sharp impulses and virtuoso finger exercises – the left side and the fundamental hearer respond to them. Long stately melodies and the processing of sound colours – that is balm for the right side and soothes the overtone hearer. It is therefore no accident that the choice of instrument of fundamental hearers is predominantly percussion, guitar, piano and high solo instruments such as trumpet and transverse flute. On the other hand, overtone hearers choose instruments that produce long sustained tones with characteristic sound colours or formants in the spectrum – strings, lower brass or woodwind, organ and voice. Differences are apparent in the way of playing. fundamental hearers like it rhythmic or virtuosic, overtone hearers prefer long melody bridges and are especially interested in sound colours and harmony. “Interestingly enough, the arrangement of preferred instruments according to fundamental and overtone hearers corresponds with the seating arrangement of a modern symphony orchestra,” said Schneider. It’s hardly a surprise that the difference between the hearer types occurs mainly in what is for mankind the most important frequency range, 1500Hz and below. It is only a short step from musical instruments to music. How does it work out in live music? Or in the mixing of a CD? When the recording engineer is a fundamental hearer and gives more value to rhythm than to tone colour, does the result then sound less good to overtone hearers? Do we find such recordings more or less pleasing? Do some musical styles therefore appeal more to us than others? Do overtone hearers prefer symphonic music, while fundamental hearers prefer a jazz concert? These are also burning questions among scientists. “For example, it is very interesting that some hi-fi set-ups have hardly any measurable differences, but are judged to sound very different,” says Dr.André Rupp, leader of the Biomagnetics Section, “is there perhaps a relationship?” AUDIO has also posed this burning question. Are we finally on the trail of the puzzle as to why some components, be they horn speakers or flat speakers, polarise the hi-fi world so much? Base tone hearers pay more attention to timing and precision. If these criteria are fulfilled, fundamental hearers perceive tonal colouring even if these have been neglected. Overtone hearers again are inclined to forgive weaknesses in rhythm rather than tolerate sound colouring. If a rather extreme overtone hearer encounters a speaker designed and tuned by a fundamental hearer, the verdict will hardly be good. Might it be, perhaps, that here lies the secret as to why some names on the hi-fi scene are celebrated by some and demonised by others?
Por si alguno de los lectores de este sitio prefiere leer el artículo en portugués, dejo el vínculo a la web de Knirsch
Lo que más me llama la atención de esto es que comentan que la repetición del test suele dar resultados semejantes, no parece que el entrenamiento influya y el hecho de que la mayoría se enclaven en un grupo o en otro y que solamente un porcentaje muy pequeño tengan un tipo de audición mixta. Me pregunto si hará falta ese tipo de audición para ser capaz de apreciar algunas diferencias entre aparatos de audio.
Si alguien tiene curiosidad por hacer el test, que me lo diga en los comentarios dejando un e-mail y le envío los archivos. Es que no soy capaz de recordar ahora de dónde los bajé..... cosas de la edad, supongo.
