Filter

A device used to affect certain parts of the spectrum of a sound, by causing the attenuation of certain frequency bands, while allowing other bands to pass unattenuated. Some common types of filters are:

  • high-pass filters (which attenuate low frequencies below the cut-off frequency);
  • low-pass filters (which attenuate high frequencies above the cut-off frequency);
  • band-pass filters (which combine both high-pass and low-pass functions);
  • band-reject filters (which perform the opposite function of the band-pass type);
  • octave, half-octave, third-octave, tenth-octave filters (which pass a controllable amount of the spectrum in each band);
  • shelving filters (which boost or attenuate all frequencies above or below the shelf point);
  • resonant or formant filters (with variable centre frequency and Q).

The Q of a filter is a measure of its resonance and is defined as the ratio of centre frequency to the bandwidth. The narrower the bandwidth, the higher the Q, and the more the filter will 'ring' or go into oscillation when stimulated by a signal with energy near the centre frequency. A constant Q filter varies its bandwidth as a function of the centre frequency, always keeping the ratio between them the same.

A group of such filters may be interconnected to form a filter bank. (Reduced from Barry Truax - Handbook for Acoustic Ecology CD-ROM Edition. Cambridge Street Publishing, 1999 - CSR-CDR 9901)

With Comb-Filtering, a sound is passed through a group of filters, generally distributed equidistantly. The mode of sound processing changes the spectral content of sounds around the selected frequencies, possibly boosting them to the extent of generating resonance, when the width of the filtered areas become very thin. Sinusoidal frequencies then start to oscillate in response to the feedback created in those frequencies. (Source - Rodolfo Caesar (1992). The Composition of Electroacoustic Music. PhD Thesis, University of East Anglia.)

Filters have also been used as musical 'instruments' in live performance, most significantly in a number of works by Karlheinz Stockhausen, including Mikrophonie I (1964), Prozession (1967), and Kurzwellen (1968). The filters were used to transform the sounds of a large tam-tam picked up by microphones moved by performers over the surface. In the latter two works the filters were also applied to the sound from a contact microphone attached to a viola. (Source - Richard Dobson (1992). A Dictionary of Electronic and Computer Music Technology. Oxford University Press.)

Filtre

Dispositif utilisé pour modifier certaines parties du spectre d'un son en atténuant des bandes de fréquences sans toucher aux autres bandes. Les principaux types de filtres sont :

  • les filtres passe-bas qui atténuent les fréquences situées au-dessus de la fréquence de coupure ;
  • les filtres passe-haut qui atténuent les fréquences situées au-dessous de la fréquence de coupure ;
  • les filtres passe-bande qui combinent un filtre passe-bas et un filtre passe-haut ;
  • les filtres coupe-bande qui sont l'opposé du filtre passe-bande ;
  • les filtres d'octave, demi-octave, tiers d'octave, dixième d'octave qui filtrent une partie du spectre dans chaque bande ;
  • les shelving filters qui augmentent ou atténuent toutes les fréquences situées au-dessus ou au-dessous du point coupure ;
  • les filtres résonants ou formant filters dont on peut modifier la fréquence et le facteur de résonance (Q).

Le facteur Q d'un filtre est une mesure de sa résonance et est défini comme le rapport de la fréquence centrale à la largeur de bande. Plus la largeur de bande est étroite, plus le facteur Q est élevé et plus le filtre résonne ou entre en oscillation lorsqu'il est stimulé par un signal possédant une énergie proche de sa fréquence centrale. Un filtre dont le facteur Q est constant modifie sa largeur de bande en fonction de la fréquence centrale en gardant toujours le même rapport entre ses deux valeurs.

Plusieurs filtres de ce type peuvent être connectés pour former une banque de filtres. (résumé à partir de Barry Truax - Handbook for Acoustic Ecology CD-ROM Edition. Cambridge Street Publishing, 1999 - CSR-CDR 9901)

Dans un filtre en peigne, le son passe à travers un ensemble de filtres distribués généralement d'une manière équidistante. Ce type de traitement du signal modifie le contenu spectral des sons autour des fréquences sélectionnées, avec la possibilité d'en augmenter le niveau au point de créer une résonance lorsque la largeur des zones filtrées devient très fine. Des fréquences sinusoïdales commencent alors à osciller en réponse aux fréquences d'entrées. (Source - Rodolfo Caesar (1992). The Composition of Electroacoustic Music. Thèse de doctorat, Université d'East Anglia.)

Les filtres ont également été utilisés comme “instruments de musique” lors de performances en direct, notamment dans certaines œuvres de Karlheinz Stockhausen : Mikrophonie I (1964), Prozession (1967) et Kurzwellen (1968). Dans la première œuvre, les filtres sont utilisés pour transformer les sons d'un grand tam-tam captés par des microphones déplacés par les musiciens sur sa surface. Dans les deux dernières œuvres, les filtres sont utilisés pour modifier les sons d'un micro-contact placé sur un alto. (Source - Richard Dobson (1992). A Dictionary of Electronic and Computer Music Technology. Oxford University Press.)

Filtro

Dispositivo utilizzato per modificare parti dello spettro di un suono, agendo su alcune delle bande di frequenza lasciando intatte le altre. I principali tipi di filtro sono: - il fitro passa-basso, che attenua le frequenze situate sopra la frequenza di taglio; - il filtro passa-alto che attenua le frequenze situate sotto la frequenza di taglio; - il filtro passa-banda che combina un filtro passa-basso e un filtro passa-alto; - il filtro a reiezione di banda o elimina banda, che funziona all'opposto del precedente; - il shelving filter che aumenta o attenua le frequenze situate sopra e sotto il valore di taglio; - i filtri risonanti o format filters nei quali si può modificare la frequenza e il fattore di risonanza (Q).

Il valore Q di un filtro corrisponde al valore della propria risonanza, e viene definito come il rapporto della frequenza centrale rispetto alla larghezza di banda. Più la larghezza di banda è stretta, più il fattore Q è elevato e più il filtro risuona nel momento in cui viene stimolato da un segnale con un'energia vicina alla frequenza centrale. Un filtro il cui fattore Q è costante modifica la propria larghezza di banda in funzione della frequenza centrale, mantenendo sempre lo stesso rapporto tra i due valori.

I vari filtri possono essere interconnessi, per formare un banco di filtri (tratto da Barry Truax, Handbook for Acoustic Ecology CD-ROM Edition, Cambridge Street Publishing, 1999 - CSR-CDR 9901).

In un filtro a pettine, il suono passa attraverso un insieme di filtri distribuiti generalmente in maniera equidistante. Questo tipo di trattamento del segnale modifica il contenuto spettrale dei suoni attorno alle frequenze selezionate, con la possibilità di aumentarne il livello al punto di creare una risonanza quando la larghezza delle zone filtrate è molto stretta. Cominciano allora a oscillare, in risposta alle frequenze entranti, delle frequenze sinusoidali. Vengono detti banco di filtri (in parallelo).

(Fonte - Rodolfo Caesar (1992). The Composition of Electroacoustic Music. Thèse de doctorat, Université d'East Anglia.).

I filtri sono stati utilizzati anche come « strumenti musicali » nelle performance live, come nel caso di alcune opere di Karlheinz Stockhausen: Mikrophonie I (1964), Prozession (1967) e Kurzwellen (1968). Nella prima opera, i filtri sono utilizzati per trasformare i suoni di un tam-tam captati da microfoni dislocati dai musicisti sulla sua superficie. Nelle ultime due, i filtri vengono utilizzati per modificare i suoni di un microfono a contatto posizionato su una viola (Fonte - (Source - Richard Dobson (1992). A Dictionary of Electronic and Computer Music Technology. Oxford University Press.).

Dispositivo che modifica lo spettro di un segnale, alterando l'ampiezza delle sue componenti frequenziali. Esistono diversi tipi di filtri, ognuno di essi con una funzione specifica. Ad esempio:

  • Filtro passa-alto, che lascia passare tutte le frequenze al di sopra di un particolare valore di taglio, attenuando quelle inferiori;
  • Filtro passa-basso, con funzione opposta a quella del precedente;
  • Filtro passa-banda, che trasmette le frequenze che si trovano fra il valore di taglio superiore e quello inferiore;
  • Filtro a reiezione di banda che elimina le componenti comprese tra i due valori.

Filter

A device used to affect certain parts of the spectrum of a sound, by causing the attenuation of certain frequency bands, while allowing other bands to pass unattenuated. Some common types of filters are:

  • high-pass filters (which attenuate low frequencies below the cut-off frequency);
  • low-pass filters (which attenuate high frequencies above the cut-off frequency);
  • band-pass filters (which combine both high-pass and low-pass functions);
  • band-reject filters (which perform the opposite function of the band-pass type);
  • octave, half-octave, third-octave, tenth-octave filters (which pass a controllable amount of the spectrum in each band);
  • shelving filters (which boost or attenuate all frequencies above or below the shelf point);
  • resonant or formant filters (with variable centre frequency and Q).

The Q of a filter is a measure of its resonance and is defined as the ratio of centre frequency to the bandwidth. The narrower the bandwidth, the higher the Q, and the more the filter will 'ring' or go into oscillation when stimulated by a signal with energy near the centre frequency. A constant Q filter varies its bandwidth as a function of the centre frequency, always keeping the ratio between them the same.

A group of such filters may be interconnected to form a filter bank. (Reduced from Barry Truax - Handbook for Acoustic Ecology CD-ROM Edition. Cambridge Street Publishing, 1999 - CSR-CDR 9901)

With Comb-Filtering, a sound is passed through a group of filters, generally distributed equidistantly. The mode of sound processing changes the spectral content of sounds around the selected frequencies, possibly boosting them to the extent of generating resonance, when the width of the filtered areas become very thin. Sinusoidal frequencies then start to oscillate in response to the feedback created in those frequencies. (Source - Rodolfo Caesar (1992). The Composition of Electroacoustic Music. PhD Thesis, University of East Anglia.)

Filters have also been used as musical 'instruments' in live performance, most significantly in a number of works by Karlheinz Stockhausen, including Mikrophonie I (1964), Prozession (1967), and Kurzwellen (1968). The filters were used to transform the sounds of a large tam-tam picked up by microphones moved by performers over the surface. In the latter two works the filters were also applied to the sound from a contact microphone attached to a viola. (Source - Richard Dobson (1992). A Dictionary of Electronic and Computer Music Technology. Oxford University Press.)

Filtro

Un dispositivo empleado para modificar ciertas partes del espectro de un sonido, que actúa provocando la atenuación de algunas bandas de frecuencia mientras otras pasan sin alteración. Entre los tipos de filtros más comunes están:

  • los filtros pasa altos o high-pass (que atenúan las frecuencias bajas, por debajo de la frecuencia de corte);
  • los filtros pasa bajos o low-pass (que atenúan las frecuencias altas, por encima de la frecuencia de corte);
  • los filtros pasa banda o band-pass (que combinan las funciones del pasa altos y la del pasa bajos);
  • los filtros rechazo de banda, de banda eliminada o band-reject (que se comportan de modo opuesto a los filtros de tipo pasa banda);
  • los filtros por octava u octave filters, 1/2 octava o half-octave filters, 1/3 de octava o third-octave filters, 1/10 octava o tenth-octave filters, etc. (que pasan una cantidad controlable del espectro de cada banda);
  • los controles de tono activos o filtros shelving (que enfatizan o atenúan todas las frecuencias por encima o por debajo de la frecuencia del escalón [frecuencia de corte] o shelf point);
  • los filtros resonantes, a modo de formantes (con Q y frecuencia central variable).

El Q de un filtro es una medida de su resonancia y se define como la relación entre la frecuencia central y el ancho de banda. Cuanto más angosto el ancho de banda, más alto el Q, y más resonará o entrará en oscilación el filtro cuando sea estimulado por una señal cuya energía esté cercana a la frecuencia central. Un filtro con Q constante varía su ancho de banda en función de la frecuencia central, siempre guardando la relación de proporcionalidad entre ambas.

Un grupo de tales filtros puede ser interconectado formando un banco de filtros. (Extractado de Barry Truax (1999). Handbook for Acoustic Ecology. CD-ROM. Cambridge Street Publishing. CSR-CDR 9901)

En el procesamiento mediante filtro peine (Comb-Filtering), un sonido pasa a través de un grupo de filtros, generalmente distribuidos de modo equidistante. El modo de procesamiento sonoro cambia el contenido espectral de los sonidos alrededor de las frecuencias seleccionadas, pudiendo reforzarlas al extremo de generar resonancias cuando el ancho de las áreas filtradas se hacen muy angostas. Las frecuencias sinusoidales comienzan entonces a oscilar en respuesta a la realimentación (feedback) creada en esas frecuencias. (Fuente: Rodolfo Caesar (1992). The Composition of Electroacoustic Music. Tesis de doctorado, University of East Anglia)

Los filtros han sido usados también como instrumentos musicales en ejecuciones en vivo, como por ejemplo en un considerable número de obras de Karlheinz Stockhausen, incluyendo Mikrophonie I (1964), Prozession (1967), y Kurzwellen (1968). En ellas los filtros fueron utilizados para transformar los sonidos de un tam-tam grande que eran capturados con micrófonos que los intérpretes movían sobre la superficie del mismo. En las últimas dos obras los filtros fueron también aplicados a los sonidos de una viola, tomados del instrumento con micrófonos de contacto. (Fuente: Richard Dobson (1992). A Dictionary of Electronic and Computer Music Technology. Oxford University Press)

References