Name: audio frequency control with passive filters
Uploaded: 2024-07-08T13:20:03.000Z
Duration: 1 min 27 s
Channel: JoVE

Prenons l’exemple d’un système de haut-parleurs audio avec des circuits de filtrage. Ces circuits transmettent sélectivement les fréquences souhaitées tout en atténuant les autres, limitant les signaux à une bande de fréquence spécifique.
Les filtres sont classés comme passifs lorsqu’ils utilisent exclusivement des composants passifs tels que des résistances, des inductances et des condensateurs.
Un filtre audio passe-bas canalise les composants basse fréquence vers le woofer ou le subwoofer, tandis qu’un filtre passe-haut dirige les composants haute fréquence vers le tweeter.
La fonction de transfert, exprimée sous la forme du rapport de tension de sortie/d’entrée, est estimée pour les basses et les hautes fréquences afin d’obtenir la réponse en fréquence souhaitée pour les circuits de filtrage.
Les filtres bien conçus transmettent des fréquences jusqu’à la fréquence de coupure sans atténuation pour les filtres passe-bas, et au-dessus de la fréquence de coupure pour les filtres passe-haut.
Un filtre passe-bande dirige les fréquences moyennes vers le haut-parleur dédié. Alors qu’un filtre d’arrêt de bande cible les fréquences qui se chevauchent pour éviter les interférences.
De même, la fonction de transfert peut être approximée pour les basses et les hautes fréquences afin d’optimiser la réponse en fréquence des filtres passe-bande et coupe-bande.
Les filtres passe-bande transmettent des fréquences autour d’une fréquence centrale, tandis que les filtres passe-bande bloquent ces fréquences.

réponse en fréquence

Les filtres passifs sont utilisés pour façonner le spectre de fréquences des signaux dans un large éventail d'applications. Ces filtres, utilisant uniquement des éléments passifs tels que des résistances (R), des inductances (L) et des condensateurs (C), sont capables d'autoriser ou de bloquer sélectivement certaines plages de fréquences sans avoir besoin de sources d'alimentation externes.
Filtres passe-bas
Les filtres passe-bas sont conçus pour transmettre des signaux dont les fréquences sont inférieures à la fréquence de coupure, ω_c, et atténuer ceux qui la dépassent. La fréquence de coupure est définie par:
<img alt="Equation 1" src="/files/ftp_upload/15148/15148_Equation_1.svg" style="height: 30px;">
Ils sont couramment utilisés pour acheminer les signaux audio vers des woofers ou des subwoofers, garantissant ainsi que seules les basses fréquences atteignent ces appareils. La fonction de transfert typique H(s) pour un filtre passe-bas RC est donnée par:
<img alt="Equation 2" src="/files/ftp_upload/15148/15148_Equation_2.svg" style="height: 30px;">
Dans cette équation, Vo est la tension de sortie, Vi est la tension d'entrée, ω est la fréquence angulaire, R est la résistance et C est la capacité.
Filtres passe-haut
En revanche, les filtres passe-haut laissent passer les fréquences supérieures à ωc tout en bloquant celles inférieures. Ces filtres sont essentiels pour diriger les composants haute fréquence vers les tweeters des systèmes audio. Un filtre passe-haut RC a la fonction de transfert suivante:
<img alt="Equation 3" src="/files/ftp_upload/15148/15148_Equation_3.svg" style="height: 30px;">
Filtres passe-bande
Les filtres passe-bande sont conçus pour laisser passer une bande de fréquences, ce qui les rend idéaux pour les canaux dédiés aux fréquences audio de milieu de gamme.
Filtres coupe-bande
Ceux-ci sont également connus sous le nom de filtres coupe-bande ; les filtres coupe-bande rejettent une bande de fréquences spécifique pour éviter les interférences, ce qui est particulièrement utile dans les systèmes électroniques complexes où plusieurs signaux se chevauchent.
La conception des filtres passifs est un équilibre délicat entre la sélection des bonnes valeurs de composants pour atteindre les fréquences de coupure et les niveaux d'atténuation souhaités.

Réponse en fréquence

Prenons l’exemple d’un système de haut-parleurs audio avec des circuits de filtrage. Ces circuits transmettent sélectivement les fréquences souhaitées tout en atténuant les autres, limitant les signaux à un ...

Education

Enseignement

JoVE Core

Electrical Engineering

Génie électrique

Unit 1

Unité 1

Frequency Response

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

Passive Filters

audio frequency control with passive filters

Passive filters shape the frequency spectrum of electrical signals. They use only passive parts such as resistors, inductors, and capacitors. Because they do not need an external power source, they can let selected frequency ranges pass or block others in many applications.

Low-pass filters pass signals below the cutoff frequency, ωc, and reduce signals above it. In audio systems, they can send bass frequencies to woofers or subwoofers. For an RC low-pass filter, the transfer function H(s) describes how the output voltage Vo relates to the input voltage Vi, the angular frequency ω, the resistance R, and the capacitance C.

High-pass filters do the opposite. They allow frequencies above ωc to pass while blocking lower frequencies. These filters are useful for sending high-frequency sound to tweeters in speaker systems. An RC high-pass filter also has a transfer function that depends on the same circuit values.

Band-pass filters pass only a chosen band of frequencies. This makes them useful for channels that handle mid-range audio. Band-stop filters, also called notch filters, reject one specific frequency band to reduce interference. They are helpful in electronic systems where several signals overlap.

Designing a passive filter means choosing the right component values. The goal is to set the desired cutoff frequencies and the right level of attenuation. That balance determines how well the circuit shapes the signal.

Audio Frequency Control with Passive Filters

audio-frequency-control-with-passive-filters

network function of a circuit

How Transfer Functions Shape Circuit Response

Transfer functions show how a circuit responds as signal frequency changes. They describe the link between input and output in frequency response analysis. This makes them useful for studying how circuits behave in electronics and engineering. A transfer function is a mathematical tool that relates phasor output to phasor input. It can be written as voltage gain, current gain, transfer impedance, or transfer admittance. The poles and zeros are the most important parts of the function. Zeros...

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Inductive Circuit Frequency Response

Inductive circuit frequency response shows how a circuit with an inductor reacts to different frequencies. The analysis starts in the time domain and then moves into the frequency domain. In that step, the inductor is replaced by an impedance, and the circuit is written with phasors, which are sinusoidal signals shown with magnitude and phase. The transfer function describes how the output changes compared with the input at each frequency. A key parameter is the time constant, which is the...

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Circuit Gain and Phase Shift

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Reading Frequency Response on Bode Plots

Bode plots show how a circuit or system responds across frequency. They use a logarithmic frequency scale on the x-axis and gain in decibels on the y-axis. This format makes it easier to display a wide range of frequencies and to see how circuit parts affect behavior over that range. A network function gives the ratio of output to input for a system. Its complex form provides both magnitude and phase angle. The logarithmic gain on a Bode plot comes from the magnitude, calculated by multiplying...

transfer function and bode plots-i

Transfer Function Gain and Origin Effects

Transfer function gain and poles or zeros at the origin shape a system's Bode plot. The transfer function is often written in standard form after the polynomial coefficients are normalized. In that form, the constant gain, zeros, poles, and quadratic terms all appear clearly. The poles and zeros mark critical frequencies where the output magnitude and phase change noticeably. The constant gain K creates a fixed magnitude and phase term. Its magnitude is 20 log 10 K in decibels, and its phase...

transfer function and bode plots-ii

Bode Plot Slope and Phase Changes

Bode plots show how a transfer function changes with frequency. The standard form includes constant gain, poles and zeros at the origin, simple poles and zeros, and quadratic poles and zeros. Each part shapes the system response in a different way. A simple zero sets the magnitude trend first. The Bode magnitude plot stays flat at low frequencies, near 0 dB, and then rises at 20 dB per decade after the corner or break frequency, ω1. That corner frequency is where the straight-line...

bode plots construction

Reading Frequency Response with Bode Plots

Bode plots show the frequency response of a system with a magnitude plot and a phase plot. Both plots use a logarithmic frequency axis. In control system analysis, this makes it easier to see how a transfer function changes with frequency. To build a Bode plot, start with the transfer function H(ω). After normalization, the function includes constant gain, zeros, and poles. Each term affects the plot in a different way. A constant gain of 10 gives a starting magnitude of 20 dB, since 20...

series resonance

Series Resonance in RLC Circuits

Series resonance in an RLC circuit happens when the inductive reactance and capacitive reactance are equal. An RLC circuit contains a resistor, an inductor, and a capacitor. The impedance of the circuit is the ratio of the supply voltage to the circuit current. At resonance, the imaginary part of the impedance becomes zero. The frequency at which this occurs is called the resonant frequency. It depends on the inductance (L) and capacitance (C) of the circuit. Mathematically, the resonant...

characteristics of series resonant circuit

characteristics-of-series-resonant-circuit

Series Resonance and RLC Filter Behavior

Series resonance in an RLC circuit happens when the inductor, capacitor, and resistor are connected in series. At the resonant frequency, the inductive reactance and capacitive reactance are equal in size but opposite in sign, so they cancel each other. As a result, the circuit impedance becomes very small and is mainly set by the resistance. The resonant frequency of a series RLC circuit can be calculated from its inductance and capacitance. At this frequency, the current reaches its maximum...

parallel resonance

Parallel RLC Tuning at Resonance

A parallel RLC circuit uses a resistor, inductor, and capacitor connected to the same nodes. Because they share the same voltage, the circuit is analyzed with admittance, which describes how easily current can flow. In a parallel RLC circuit, admittance helps show how the circuit responds as the frequency changes. Resonance happens when the net reactance is zero. At that point, the capacitive and inductive effects cancel each other out. The resonant frequency is found from this condition. At...

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Op Amp Gain and Bode Plot Basics

Operational amplifiers are used for signal conditioning, filtering, and mathematical tasks such as addition, subtraction, integration, and differentiation. Their frequency response shows how amplifier gain changes as the input frequency changes. This makes the gain of an op-amp a key idea in circuit design. At low frequencies, an op-amp can hold a constant gain called the dc gain, A0. As frequency rises, the gain starts to drop after the corner frequency, or break frequency, ω1. In other...

passive filters

Passive filters shape the frequency spectrum of electrical signals. They use only passive parts such as resistors, inductors, and capacitors. Because they do not need an external power source, they can let selected frequency ranges pass or block others in many applications. Low-pass filters pass signals below the cutoff frequency, ωc, and reduce signals above it. In audio systems, they can send bass frequencies to woofers or subwoofers. For an RC low-pass filter, the transfer function H(s)...

active filters

Active Filter Design and Frequency Response

Active filters use op-amps, resistors, and capacitors to shape a signal's frequency response. They remove unwanted frequency components while keeping the parts of the signal that are needed. The design depends on the choice of resistor and capacitor values, which set the cutoff points and help define the overall response. A first-order low-pass active filter passes signals below a cutoff frequency and reduces signals above it. Its transfer function includes the low-frequency gain, also called...

scaling

Circuit Component Scaling for Filters

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design example

Touch-Tone Filter Design Example

Touch-tone telephony uses dual-tone multi-frequency (DTMF) signaling and a filter design example to show how keypad tones are separated. It replaced the old rotary dial with a matrix-style keypad arranged in four rows and three columns. Each of the 12 buttons produces a unique signal pair. Every key press creates two sinusoidal tones at the same time. One tone comes from a low-frequency group between 697 and 941 Hz. The other comes from a high-frequency group between 1209 and 1477 Hz. This...

key terms and concepts

Learn how passive filters use resistors, inductors, and capacitors to pass or block sound frequencies in low-pass, high-pass, band-pass, and notch filters.

Audio Frequency Control with Passive Filters | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

Audio Frequency Control with Passive Filters

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