Equalizer Design for Sound Reproduction

Juho Liski

Equalizer Design for Sound Reproduction

Julkaisun otsikon käännös: Ekvalisaattorien suunnittelu äänentoistoon

Juho Liski

Audio Signal Processing

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Digitaalisia graafisia ekvalisaattoreita käytetään laajalti erilaisissa sovelluksissa, kuten musiikin tuotannossa ja äänentoistossa, signaalien magnitudivasteen muokkaamiseen. Niiden käyttäminen on vaivatonta, sillä ainoat säädettävät parametrit ovat kaistojen vahvistukset. Ekvalisaattori voidaan toteuttaa eri kaistajaoilla ja rakenteilla, jolloin se soveltuu tiettyihin sovelluksiin tai tietylle laitteistolle. Graafisen ekvalisaattorin suunnittelu ei kuitenkaan ole helppoa kaistojen vuorovaikutuksen takia, joka johtaa epätarkkuuteen. Tämä on erityisen ongelmallista automaattista suunnittelua hyödyntävissä sovelluksissa, kuten kuulokkeiden tai kaiuttimien adaptiivisessa ekvalisoinnissa melussa. Tällöin ekvalisaattorin pitäisi tuottaa algoritmin määrittämä tavoitevaste tarkasti ja tehokkaasti. Tässä työssä keskitytään graafisten ekvalisaattorien tarkkaan suunnitteluun ja niiden sovelluksiin. Ensimmäisessä osassa käsitellään eri ekvalisaattorirakenteita ja kehitetään uusi rinnakkaisekvalisaattori viivästetyllä IIR-osalla. Melkein kaikki ekvalisaattorit saavuttavat ±1 dB:n tarkkuuden hyödyntäen suodattimia, joiden vastetta voidaan tarkasti hallita kolmessa pisteessä. Kaikkien kaistasuodattimien vahvistus optimoidaan kerralla pienimmän neliösumman menetelmällä, joka ottaa kaistojen vuorovaikutuksen huomioon. Suurin tarkkuus saavutetaan, kun suunnittelupisteitä on kaksinkertainen määrä kaistoihin nähden, suodattimilla on symmetrinen magnitudivaste aina korkeille taajuuksille asti ja tarvittavat parametrit optimoidaan jokaiselle rakenteelle erikseen. Työn toisessa osassa keskitytään kuuloke-ekvalisointisovelluksiin. Esitetyt algoritmit käyttävät adaptiivisia suodattimia läpikuuluvuusprosessointiin ja kuulokevasteen personointiin. Ensin mainitussa estimoidaan kuulokkeen vaimennus ja ohjataan ekvalisaattoria läpikuuluvuuden saavuttamiseksi kuulokkeen istuvuudesta riippumatta. Jälkimmäinen hyödyntää samaa adaptiivista suodatinta kuulokkeen magnitudivasteen estimointiin. Mittaukset osoittivat, että vasteen estimointi ja sen ekvalisointi haluttuun tavoitteeseen toimivat tarkasti. Työn viimeisessä osassa käsitellään kaiutinten magnitudi- ja vaihe-ekvalisointia. Paneeli-kaiuttimien äänenlaatua parannetaan mittaamalla ensin usean kaiuttimen magnitudevaste ja muokkaamalla vasteita ekvalisaattoreilla. Ekvalisaattorit suunniteltiin yksipistemenetelmällä. Toisaalta simuloidun kaiuttimen ryhmäviive ekvalisoidaan osoittaen, että rajatun kaistan ryhmäviivetasoitus toimii paremmin kuin koko kaistan. Esitellyt graafiset ekvalisaattorit soveltuvat monenlaisiin, niin ihmisten kuin algoritmien ohjaamiin audiojärjestelmien ekvalisointisovelluksiin. Eri rakenteet soveltuvat eri laitteistoille, ja käsiteltyjen ekvalisaattorien yksinkertainen rakenne, joka sisältää ainoastaan yhden toisenasteen suodattimen kaistaa kohden, soveltuu erityisen hyvin mobiililaitteille.

Julkaisun otsikon käännös	Ekvalisaattorien suunnittelu äänentoistoon
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Välimäki, Vesa, Vastuuprofessori Rämö, Jussi, Ohjaaja Välimäki, Vesa, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-64-0039-6
Sähköinen ISBN	978-952-64-0040-2
Tila	Julkaistu - 2020
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

akustinen signaalinkäsittely
audiojärjestelmät
digitaaliset suodattimet
ekvalisaattorit
IIR-suodattimet
polynomit

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http://urn.fi/URN:ISBN:978-952-64-0040-2

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Ville Pulkki (Manager)
Sähkötekniikan korkeakoulu
Laitteistot/tilat: Facility

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@phdthesis{2f59303e99154877aa675b9cac6dbf0a,

title = "Equalizer Design for Sound Reproduction",

abstract = "Digital graphic equalizers are widely used in various applications, such as music production and reproduction, to control the magnitude responses of signals. They are straightforward to operate, with the gain at each band being the only controllable parameter. Different band divisions and different equalizer structures are used based on the requirements of the application or the available hardware. However, the accurate design of graphic equalizers is not straightforward due to band leakage, i.e., the interaction of the neighboring band filters leading to approximation errors. This is especially problematic in applications utilizing automatic equalizer updates, such as the adaptive equalization of headphones or loudspeakers based on ambient noise. In these applications, the target curve must be realized accurately and efficiently. This thesis focuses on accurate graphic-equalizer design and its applications. The first part discusses different equalizer structures and proposes a novel parallel graphic equalizer with a delayed IIR part. Almost all discussed designs achieve an accuracy of ±1 dB with the help of band filters whose responses are exactly controlled at three points. A least-squares method jointly optimizes the filter gains and accounts for the band leakage. It is shown that the number of design points should be double the number of bands, the accuracy is increased with band filters having a symmetric shape up to the Nyquist frequency, and the design parameters must be optimized for each design separately. The second part of the thesis discusses equalizer applications related to headphones. The proposed algorithms apply adaptive filters to hear-through processing and to individualization of the headphone response. The former algorithm estimates the isolation of the headphones and controls the equalizer in order to achieve acoustic transparency despite changes in the headphone fit. The latter example applies a similar adaptive filter to estimate the headphone magnitude response, which is then equalized to a selected target. Measurements indicate that both the magnitude-response estimation and equalization work accurately. The final part of the thesis focuses on loudspeaker equalization, and both the magnitude-only and phase equalization are elaborated. Multiple flat-panel loudspeakers are measured, and their sound is improved using a single-point equalizer design. A simulated loudspeaker is group-delay equalized with a frequency-sampled FIR filter, and a limited-band equalizer is shown to be supe- rior to the full-band group-delay equalization. The proposed accurate equalizers are suitable for a wide range of audio system equalization applications, both human- and algorithm-operated ones. The different structures enable the equalizers to be run on different hardware, and the low complexity of the equalizers comprising a single second-order section per band makes them especially suitable for mobile implementations.",

keywords = "acoustic signal processing, audio systems, digital filters, equalizers, IIR filters, polynomials, akustinen signaalink{\"a}sittely, audioj{\"a}rjestelm{\"a}t, digitaaliset suodattimet, ekvalisaattorit, IIR-suodattimet, polynomit, acoustic signal processing, audio systems, digital filters, equalizers, IIR filters, polynomials",

author = "Juho Liski",

year = "2020",

language = "English",

isbn = "978-952-64-0039-6",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "140",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Equalizer Design for Sound Reproduction

AU - Liski, Juho

PY - 2020

Y1 - 2020

N2 - Digital graphic equalizers are widely used in various applications, such as music production and reproduction, to control the magnitude responses of signals. They are straightforward to operate, with the gain at each band being the only controllable parameter. Different band divisions and different equalizer structures are used based on the requirements of the application or the available hardware. However, the accurate design of graphic equalizers is not straightforward due to band leakage, i.e., the interaction of the neighboring band filters leading to approximation errors. This is especially problematic in applications utilizing automatic equalizer updates, such as the adaptive equalization of headphones or loudspeakers based on ambient noise. In these applications, the target curve must be realized accurately and efficiently. This thesis focuses on accurate graphic-equalizer design and its applications. The first part discusses different equalizer structures and proposes a novel parallel graphic equalizer with a delayed IIR part. Almost all discussed designs achieve an accuracy of ±1 dB with the help of band filters whose responses are exactly controlled at three points. A least-squares method jointly optimizes the filter gains and accounts for the band leakage. It is shown that the number of design points should be double the number of bands, the accuracy is increased with band filters having a symmetric shape up to the Nyquist frequency, and the design parameters must be optimized for each design separately. The second part of the thesis discusses equalizer applications related to headphones. The proposed algorithms apply adaptive filters to hear-through processing and to individualization of the headphone response. The former algorithm estimates the isolation of the headphones and controls the equalizer in order to achieve acoustic transparency despite changes in the headphone fit. The latter example applies a similar adaptive filter to estimate the headphone magnitude response, which is then equalized to a selected target. Measurements indicate that both the magnitude-response estimation and equalization work accurately. The final part of the thesis focuses on loudspeaker equalization, and both the magnitude-only and phase equalization are elaborated. Multiple flat-panel loudspeakers are measured, and their sound is improved using a single-point equalizer design. A simulated loudspeaker is group-delay equalized with a frequency-sampled FIR filter, and a limited-band equalizer is shown to be supe- rior to the full-band group-delay equalization. The proposed accurate equalizers are suitable for a wide range of audio system equalization applications, both human- and algorithm-operated ones. The different structures enable the equalizers to be run on different hardware, and the low complexity of the equalizers comprising a single second-order section per band makes them especially suitable for mobile implementations.

AB - Digital graphic equalizers are widely used in various applications, such as music production and reproduction, to control the magnitude responses of signals. They are straightforward to operate, with the gain at each band being the only controllable parameter. Different band divisions and different equalizer structures are used based on the requirements of the application or the available hardware. However, the accurate design of graphic equalizers is not straightforward due to band leakage, i.e., the interaction of the neighboring band filters leading to approximation errors. This is especially problematic in applications utilizing automatic equalizer updates, such as the adaptive equalization of headphones or loudspeakers based on ambient noise. In these applications, the target curve must be realized accurately and efficiently. This thesis focuses on accurate graphic-equalizer design and its applications. The first part discusses different equalizer structures and proposes a novel parallel graphic equalizer with a delayed IIR part. Almost all discussed designs achieve an accuracy of ±1 dB with the help of band filters whose responses are exactly controlled at three points. A least-squares method jointly optimizes the filter gains and accounts for the band leakage. It is shown that the number of design points should be double the number of bands, the accuracy is increased with band filters having a symmetric shape up to the Nyquist frequency, and the design parameters must be optimized for each design separately. The second part of the thesis discusses equalizer applications related to headphones. The proposed algorithms apply adaptive filters to hear-through processing and to individualization of the headphone response. The former algorithm estimates the isolation of the headphones and controls the equalizer in order to achieve acoustic transparency despite changes in the headphone fit. The latter example applies a similar adaptive filter to estimate the headphone magnitude response, which is then equalized to a selected target. Measurements indicate that both the magnitude-response estimation and equalization work accurately. The final part of the thesis focuses on loudspeaker equalization, and both the magnitude-only and phase equalization are elaborated. Multiple flat-panel loudspeakers are measured, and their sound is improved using a single-point equalizer design. A simulated loudspeaker is group-delay equalized with a frequency-sampled FIR filter, and a limited-band equalizer is shown to be supe- rior to the full-band group-delay equalization. The proposed accurate equalizers are suitable for a wide range of audio system equalization applications, both human- and algorithm-operated ones. The different structures enable the equalizers to be run on different hardware, and the low complexity of the equalizers comprising a single second-order section per band makes them especially suitable for mobile implementations.

KW - acoustic signal processing

KW - audio systems

KW - digital filters

KW - equalizers

KW - IIR filters

KW - polynomials

KW - akustinen signaalinkäsittely

KW - audiojärjestelmät

KW - digitaaliset suodattimet

KW - ekvalisaattorit

KW - IIR-suodattimet

KW - polynomit

KW - acoustic signal processing

KW - audio systems

KW - digital filters

KW - equalizers

KW - IIR filters

KW - polynomials

M3 - Doctoral Thesis

SN - 978-952-64-0039-6

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Equalizer Design for Sound Reproduction

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