Noise

In contrast to most 'musical' sounds, which have a definite pitch and a predominantly harmonic spectrum, noise consists of a theoretically infinite and continuous range of frequencies. The waveform consists not of regular periodic cycles but of random fluctuations of amplitude. In the present context, the bandwidth of the noise may be considered limited to that of human hearing. As will be seen, it is possible to speak of noise limited to a variety of bandwidths.

It is usual to use analogies to visible light when discussing different types of noise. Thus, noise, which has equal intensity at all frequencies, is referred to as 'white noise'. Because the human ear is more sensitive to high than to low frequencies, white noise will be heard as a high hissing sound.

By passing white noise through a filter, different 'colours' can be obtained. 'Pink noise' results if white noise is passed through a mildlow-pass filter. Whereas white noise has equal power at all frequencies, pink noise is defined as having equal power in each octave band (corresponding more closely to the response of the ear). Thus the power varies inversely with frequency - for this reason it is often referred to as '1/f noise'. Similarly 'red noise' is referred to as '1/f (Squared) noise', the high frequencies being much more attenuated than in pink noise. (Source - Richard Dobson (1992). A Dictionary of Electronic and Computer Music Technology. Oxford University Press.)

Bruit

Contrairement à la plupart des sons “musicaux” ayant une hauteur définie et un spectre avec une prédominance harmonique, le bruit est théoriquement composé d'une infinité de fréquences dans un intervalle continu. La forme d'onde d'un bruit n'est pas constituée de cycles périodiques réguliers mais de variations aléatoires de l'amplitude. Dans le cas présent, la largeur de bande du bruit n'est limitée que par celle de l'oreille humaine. Comme nous allons le voir, il est possible d'avoir des bruits limités à une variété de largeurs de bandes.

Il est habituel d'utiliser des analogies liées à la lumière visible lorsque l'on décrit différents types de bruits. Ainsi, le bruit qui a une intensité égale sur toutes les fréquences, est désigné sous le nom de “bruit blanc”. Comme l'oreille humaine est plus sensible dans les aigus que dans les basses fréquences, le bruit blanc sera perçu comme un bruit de sifflement aigu.

En passant le bruit blanc dans un filtre, différentes “couleurs” peuvent être obtenues. Le “bruit rose” résulte d'un bruit blanc dans un filtre laissant passer les fréquences médiums. En considérant que le bruit blanc à des fréquences d'égale intensité, le bruit rose est définit comme ayant une puissance égale dans chaque bande d'octave (correspondant mieux à la réponse de l'oreille). Ainsi, la puissance est inversement proportionnelle à la fréquence - pour cette raison, le bruit rose est souvent désigné sous le nom de “bruit 1/f”. De même, le “bruit rouge” est souvent désigné comme le “bruit (carré) 1/f”, les hautes fréquences étant beaucoup plus atténuées que dans le bruit rose. (Source - Richard Dobson (1992). A Dictionary of Electronic and Computer Music Technology. Oxford University Press.)

Rumore

A differenza dela maggior parte dei suoni “musicali”, che mostrano una frequenza definita e una componente spettrale armonica, il rumore consiste in una serie potenzialmente infinita e continua di frequenze. La sua forma d'onda non è fatta di cicli periodici regolari, ma di fluttuazioni casuali in ampiezza. Nel contesto qui presente, la larghezza di banda di rumore viene limitata all'ambito udibile dall'orecchio umano. Come si vedrà qui di seguito, si può parlare di rumore limitato ad uno specifico range di bande.

Normalmente, per parlare dei vari tipi di rumore si fa riferimento ad alcune analogie con la luce. Pertanto, un rumore che ha uguale intensità a tutte le frequenze è detto “rumore bianco”. Poiché l'orecchio umano è più sensibile alle alte frequenze, piuttosto che alle basse, il rumore bianco viene percepito come un suono alto e sibilante. Se si passa un rumore bianco attraverso un filtro, si ottengono vari “colori”. Il “suono rosa” è un rumore bianco passato attraverso un filtro che lascia filtrare le frequenze medie. Mentre il rumore bianco ha una dinamica uguale in tutte le frequenze, il rumore rosa ha una dinamica costante per ogni ottava di banda (ciò che lo assimila di più alla risposta dell'orecchio umano). Inoltre, poiché la potenza è inversamente proporzionale alla frequenza, per il rumore rosa si parla spesso di “rumore 1/f”. Allo stesso modo, il “suono rosso” viene detto “rumore (quadrato) 1/f”, poiché le alte frequenze sono molto più attenuate che nel rumore rosa. (Fonte - Richard Dobson (1992). A Dictionary of Electronic and Computer Music Technology. Oxford University Press.).

Lärm

In contrast to most 'musical' sounds, which have a definite pitch and a predominantly harmonic spectrum, noise consists of a theoretically infinite and continuous range of frequencies. The waveform consists not of regular periodic cycles but of random fluctuations of amplitude. In the present context, the bandwidth of the noise may be considered limited to that of human hearing. As will be seen, it is possible to speak of noise limited to a variety of bandwidths.

It is usual to use analogies to visible light when discussing different types of noise. Thus, noise, which has equal intensity at all frequencies, is referred to as 'white noise'. Because the human ear is more sensitive to high than to low frequencies, white noise will be heard as a high hissing sound.

By passing white noise through a filter, different 'colours' can be obtained. 'Pink noise' results if white noise is passed through a mildlow-pass filter. Whereas white noise has equal power at all frequencies, pink noise is defined as having equal power in each octave band (corresponding more closely to the response of the ear). Thus the power varies inversely with frequency - for this reason it is often referred to as '1/f noise'. Similarly 'red noise' is referred to as '1/f (Squared) noise', the high frequencies being much more attenuated than in pink noise. (Source - Richard Dobson (1992). A Dictionary of Electronic and Computer Music Technology. Oxford University Press.)

Ruido

En contraste con la mayoría de los sonidos "musicales", que tienen una altura definida y un espectro predominantemente armónico, el ruido consiste de un teoricamente infinito y continuo rango de frecuencias. La forma de onda no consiste de ciclos periódicos regulares sino de fluctuaciones aleatorias de amplitud. En este contexto, el ancho de banda del ruido puede considerarse limitado al de la audición humana. Como se verá, es posible hablar de bandas de ruido limitadas según diferentes tipos de bandas.

Es usual emplear analogías con la luz visible cuando se habla de los diferentes tipos de ruido. De ese modo, el ruido que tiene igual intensidad en todas las frecuencias, es llamado "ruido blanco". Dado que el oído humano es más sensible a las altas que a las bajas frecuencias, el ruido blanco sera escuchado como un siseo agudo (hissing sound).

Pasando ruido blanco a través de un filtro, se pueden obtener diferentes "colores". El "ruido rosa" se consigue cuando el ruido blanco pasa a través de un filtro pasa-bajos de pendiente suave. Mientras que el ruido blanco tiene igual energía en todas las frecuencias, el ruido rosa se define como aquel que tiene igual energía por octava (lo que corresponde más ajustadamente a la respuesta del oído). Entonces, la energía varía inversamente con la frecuencia -por esta razón se lo llama frecuentemente "ruido 1/ƒ". De modo similar, el "ruido rojo", donde las altas frecuencias están mucho más atenuadas que en el ruido rosa, es llamado "ruido 1/ƒ2".

(Fuente: Richard Dobson (1992). A Dictionary of Electronic and Computer Music Technology. Oxford University Press)

References