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Digital Filters

abstract

Digital filters are used for two general purposes: (1) separation of signals that have been combined, and (2) restoration of signals that have been distorted in some way. Analog (electronic) filters can be used for these same tasks; however, digital filters can achieve far superior results. The most popular digital filters are described and compared in the next seven chapters. This introductory chapter describes the parameters you want to look for when learning about each of these filters. Digital filters are a very important part of DSP. In fact, their extraordinary performance is one of the key reasons that DSP has become so popular. As mentioned in the introduction, filters have two uses: signal separation and signal restoration. Signal separation is needed when a signal has been contaminated with interference, noise, or other signals. For example, imagine a device for measuring the electrical activity of a baby's heart (EKG) while still in the womb. The raw signal will likely be corrupted by the breathing and heartbeat of the mother. A filter might be used to separate these signals so that they can be individually analyzed. Signal restoration is used when a signal has been distorted in some way. For example, an audio recording made with poor equipment may be filtered to better represent the sound as it actually occurred. Another example is the deblurring of an image acquired with an improperly focused lens, or a shaky camera.

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Digital Filters

abstract

Digital filters are used for two general purposes: (1) separation of signals that have been combined, and (2) restoration of signals that have been distorted in some way. Analog (electronic) filters can be used for these same tasks; however, digital filters can achieve far superior results. The most popular digital filters are described and compared in the next seven chapters. This introductory chapter describes the parameters you want to look for when learning about each of these filters. Digital filters are a very important part of DSP. In fact, their extraordinary performance is one of the key reasons that DSP has become so popular. As mentioned in the introduction, filters have two uses: signal separation and signal restoration. Signal separation is needed when a signal has been contaminated with interference, noise, or other signals. For example, imagine a device for measuring the electrical activity of a baby's heart (EKG) while still in the womb. The raw signal will likely be corrupted by the breathing and heartbeat of the mother. A filter might be used to separate these signals so that they can be individually analyzed. Signal restoration is used when a signal has been distorted in some way. For example, an audio recording made with poor equipment may be filtered to better represent the sound as it actually occurred. Another example is the deblurring of an image acquired with an improperly focused lens, or a shaky camera.

Digital Filters


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What are Digital Filters?
Digital filters that incorporate digital-signal-processing (DSP) techniques have received a great deal of attention in technical literature in recent years. Although they rarely serve as anti-aliasing filters (in fact, they need anti-aliasing filters), digital filters merit discussion here because digital filters offer features that have no counterparts in other filter technologies. You can do things utilizing digital filters (unlimited flexibility) that may not be possible in the analog world.
DSP represent a growing subset of signal-processing activities that utilize an A/D converter to turn an analog signal into a stream of digital data. An extensive sequence of multiplication's and additions then operate on those data. In some cases, a D/A converter creates an analog equivalent signal at the output of the processed stream. DSP techniques can perform functions such as fast-Fourier transform (FFT), delay equalization, programmable gain, modulation, encoding/decoding, and digital filtering. Figure 1 shows a typical digital filter configuration.


Who are we?
Frequency Devices - founded in 1968 to provide electronic design engineers with analog signal solutions and engineering services - designs and manufactures standard and custom electronic analog and digital filters, amplifier and oscillator components and instrument products for signal conditioning, signal processing and signal analysis. By addressing a wide array of signal processing needs, Frequency Devices continues to provide state-of-the-art solutions to the rapidly changing electronics industry. >From prototype to production, Frequency Devices designs and manufactures products to agreed-upon performance specifications, utilizing the latest analog and digital technologies.

How can we help you?
Frequency Devices has posted for your information and reference purposes an "Electronic Filter Design Guide" which you may download from our web site or view online at no cost. It covers all of the basic concepts of electronic analog and digital filter design, and describes many of the design considerations and problems that will be encountered by electronic filter design engineers. Our analog and digital filter design guide reflects our more than 30 years of experience in the field.