Beschreibung. Suppose you want to test the audio response of a system through the frequency range from 20 to 2000 Hz. Signal Processing Stack Exchange is a question and answer site for practitioners of the art and science of signal, image and video processing. How can I implement a digital anti-aliasing filter in Python. No, this does not make sense. Figure 1 shows the general circuit diagram for this type of application. To learn more, see our tips on writing great answers. 3. The actual chain is: Analog Input. The traditional solution is to insert anti-alias lowpass filters into your input signal path prior to sampling, and then sample at the intended rate for your data set. The anti-aliasing filter is a lowpass filter meant to attenuate signals above the Nyquist frequency to prevent aliased signals. So, the AAMFILT processing compromises a little. Any frequencies above 24100 Hz will alias back to the audible range (below 20kHz). How can I separate the lid from a can that has a pull-tab/ring without flinging food everywhere? The president of Precision Filters, Inc., Doug Firth discusses the concept of aliasing and how to prevent aliasing using an analog low-pass filter. Filter Amplifier Bandwidth Anti-Alias Filter Sensor Bandwidth ADC’s Digital Filter ADC Output , = , ∗ 2 + , ∗ 2 + , ∗ 2 + , ∗ 2 + , ∗ 2 Such very high sample rates would have been beyond all reason with older technology, but they are a routine matter for xDAP systems [3]. We will be faced with another Goldilocks decision: Bessel, Butterworth, Elliptical, or … Anybody who has used a digital filter will know that its frequency response characteristic is tied to the sampling rate of its data stream. How do you expect your digital filter to produce different outputs when fed the same input? That's a great comment. An anti-aliasing analog lowpass filter should exhibit a flat passband frequency response with a good high-frequency alias rejection and a fast roll-off in the transition band. Anti-Aliasing-Filter erklären. 20000Hz bis 24100 sind ungefähr eine Vierteloktave. What is the crystal structure of ammonium hydrogen sulfate? Aliasing would be a big problem for digital audio, because it is usually not desired for frequencies to change in a signal. It's beautifully birefringent. I agree with pichenettes's answer but I would like to add that it is pretty common practice to use a simple inexpensive low-order analog anti-aliasing filter, and do the rest of the anti-aliasing filtering in the digital domain. This is in general not true (although I understand what you mean). As discussed in many articles, the higher the oversampling frequency, the easier the analog filter design becomes. This implies of course that you do not process at maximum sampling rate but that you downsample after the digital anti-aliasing filter. Analog Anti-aliasing filter. However, this is not really correct — you do not need filtering if the signal is already suitably bandlimited at the time you capture your samples. The only thing that could work would be to sample the input signal as fast as your ADC allows, and then downsample it in the digital domain to your target sample rate - but unless you have CPU cycles to waste, you'd better use an analog filter upstream. Manufacturers claim this makes images sharper though it comes with an increase in moiré patterns. Thanks for contributing an answer to Signal Processing Stack Exchange! In communication sys-tems, filters are used for tuning in specific frequencies and eliminating others. The 4303 automatically sets this based on the sampling rate. Filtertyp. To test how the filters affected the data, R.C. a DAQ system, it is usually necessary to place an anti- aliasing filter before the analog-to-digital converter (ADC) to rid the analog system of higher-frequency noise and signals. It only takes a minute to sign up. After this, simple decimation is completely safe. In addition, as the converter’s sampling rate changes, an anti-aliasing filter’s passband should increase or decrease accordingly. To avoid the ValueError: "Digital filter critical frequencies must be 0 < Wn < 1" I set Wn to 0.99, which I understand means that frequencies above 0.99 * Nyquist frequency = 0.99 * 500 kHz = 495 kHz are cut off. Digital Anti-Alias Filters. For a simple anti-aliasing filter, often times a simple single-pole passive RC filter is acceptable. An illustration of an anti-aliasing filter being applied to a raw signal is shown below. The side effect of using elevated sampling rates is a massive and redundant data set. Figure 1 shows the general circuit diagram for this type of application. Frequenzen oberhalb einer Grenzfrequenz können das Filter passieren. The 4303 automatically sets this based on the sampling rate. The anti-aliasing filters attenuate the unnecessary high-frequency components of a signal. Digitaler Anti-Aliasing-Filter. Does your data acquisition system, your analog-digital converter need an analog anti-aliasing filter or not? https://dsp.stackexchange.com/questions/9205/can-we-have-a-digital-anti-aliasing-filter With a DUE, you can have a digital filtering in between 2 DMA ADC conversions, triggered by … If you decide that you need to change the sampling rate for some reason, this probably means that your digital filters must be redesigned to keep your filter cutoff frequency more or less the same. Why did Visual Basic use parentheses for both function call and array access? It is corrected with a digital equalizer prior to the AD conversion. Hi guys, I am trying to measure some voltages with Arduino Due using analogRead. How can I implement a digital anti-aliasing filter in Python. Digital signal processing sys-tems use filters to prevent the aliasing of out-of-band noise and interference. The filtering removes that white band completely. Optical Low Pass Filter Application. Anti-aliasing filter effective noise bandwidth Anti-Alias (RC) Filter -3 dB Cutoff (f-3dB ... Quiz: Noise bandwidth including digital filters ADC Amplifier AIN0 AIN1 Sensor BW = 10MHz e n = 2nV/ OHz Vcc BW = 500kHz e n = 1nV/ OHz BW = 50MHz e n = 2nV/ OHz BW = 1MHz e n = 0.6nV/ OHz BW = 100kHz e n = 0.8nV/ OHz 2. aliasing filter before the analog-to-digital converter (ADC) to rid the analog system of higher-frequency noise and signals. Anti-Aliasing, Analog Filters for Data Acquisition Systems INTRODUCTION Analog filters can be found in almost every electronic circuit. Clock the data through twice as fast, and the effective filter passband doubles in width. A function generator produced a 20-Hz square wave and a DATAMAX 16-bit instrumentation data acquisition system recorded the effects of the filter. Asking for help, clarification, or responding to other answers. The current technology provides for highly precise SAR ADC conversion rates that have increased considerably in recent years, and currently reach from over 1 MSPS up to 15 MSPS for 18-bit resolution. The actual chain is: The further illustrate, consider the following: The following book is an excellent, clear resource for these sort of things. Most of the information returned in the data set is unusable, distorted by the rolloff characteristics of the filter. Instead, there is a transition band between the frequencies that are completely preserved and high frequencies that are completely rejected. What you say is certainly true for audio applications (in which ready to use, integrated codec chips replaced ADC/DAC a long time ago) - but there are many fields of engineering in which the acquisition is still done by vanilla SAR ADCs (as standalone chips or built into microcontrollers) - and with these you have to do the hard work! The first step in designing this filter is to select the desired cutoff frequency, f C. But careful analysis reveals that to preserve the desired low frequency band with 14-bit accuracy (a slight compromise), while also guaranteeing −60dB high-frequency rejection of any aliasing effects (sometimes a compromise), the sampling frequency must be higher than the preserved band by a factor of 50. An anti-aliasing filter is Is it possible to observe strong gravitational lensing with amateur telescopes? We now know that an ADC must sample the input signal slightly faster than the Nyquist rate to properly represent it in the digital domain. There is no aliasing into the band that you care about, because there is nothing left to alias. Question: A 3rd Order Butterworth Anti-aliasing Filter Is To Be Designed For A DSP System. I am working on a board that has no antialisaing filter at the input of the ADC. Avoid Aliasing by Decimation with Digital filters . Bypassing a voltage regulator if input voltage is too low. The anti-aliasing would have a cut-off frequency of 20 KHz, but since this is not an ideal filter usually the sampling frequency used goes from 44.1 KHz to 96 KHz, allowing a transition band of at least 2 KHz. ADC Architecture: SAR vs. delta-sigma ADCs . Manufacturers claim this makes images sharper though it comes with an increase in moiré patterns. Use the circuit from the previous problem. Aliasing would be a big problem for digital audio, because it is usually not desired for frequencies to change in a signal. Anti-Aliasing Filter. Your spectrum will show this kind of shape regardless of the rate you select. This filter is an anti-alias filter because by attenuating the higher frequencies (greater than the Nyquist frequency), it prevents the aliasing components from being sampled. Für das Verständnis der weiteren Elektronik-Minikurse zum Thema SC-Filter genügen jedoch diese Grundlagen hier. Actually, 900Hz will be negative of the 100Hz size wave. To preserve the accuracy in the band of frequencies you care about, the cutoff frequency of the filter must be considerably higher than the preserved band. Digitale I/O; Controller im Chassis; CompactDAQ-Chassis; Temperatur; Schall und Schwingung; Dehnung, Druck und Kraft ; Testen elektronischer Schaltungen; Oszilloskope; Schaltmodule; Source Measurement Units; GPIB, Ethernet und serielle Schnittstellen; Digitalmultimeter ; PXI Controllers; PXI Chassis; Entwerfen und Testen drahtloser Systeme. As a source of low to midrange noise to drive the test, apply your favorite Metallica album [1]. The sampling rate, anti-aliasing filter and signal interpolation filter dependence on the digital timing were studied in this work. Alle Frequenzen über 24100 Hz werden auf den hörbaren Bereich (unter 20 kHz) zurückgeführt. Anti-Aliasing Filter Analysis for Digital Cameras Russ Palum; Eastman Kodak Company, Rochester, NY/USA Abstract Anti-aliasing filters have been used in video cameras since Pritchard patented the first filter for RCA in 1971. The AAMFILT processing enforces the following rolloff envelope. filter features unity gain in the pass band with no gain variation and a level of alias attenuation that matches the theoretical dynamic range of the data conversion system in use. Connect and share knowledge within a single location that is structured and easy to search. In theory, only an infinite-length filter can preserve all of your signal band perfectly to the Nyquist limit at the reduced sampling rate. Confused on application of Anti-Aliasing Filter. To test how the filters affected the data, R.C. In the latter case, the filter prevents imaging, the reverse process of aliasing where in-band frequencies are mirrored out of band. So, -900, 1100, 2100 etc. The AAMFILT processing, however, does not have this problem. Which antialiasing filter before equispaced sampling, Digital Anti Aliasing Filter For Waveform Band Limiting. Instead of removing extraneous frequencies prior to aliasing, the digital approach uses a much higher sampling rate and captures all of the signal power, including the extraneous frequencies well above the ones that you specifically care about. It seems like this should work well. Making statements based on opinion; back them up with references or personal experience. Steve W-- hide signature --Two things are infinite: the universe and human stupidity; and I’m not sure about the universe! Because you apply the anti-aliasing filter to the analog signal before it is converted to a digital signal, the anti-aliasing filter is an analog filter. What about equivalent time sampling? Sampled data can be further down sampled using digital anti alias filter, sometimes also referred to as a decimation filter. Then apply linear phase digital filter between 20kHz and 24.1kHz. Audio systems use them for preamplification, equalization, and tone control. Actually, when you take into account the known damage that a theoretically perfect filter would cause, disregarding the practical hardware limitations, the results are not close to best possible. Hochpass. But what about 250 KHz? After you have digitized the samples, there is no way to reverse any aliasing damage done to your data set. Does "upset victory" means a victory that people are not happy about? Aliasing is not necessarily bad thing, when you have additional information about the frequency band of your waveform, so that you can mathematically reconstruct the waveform shape by appropriately shuffling the sample values. The analog filter can be kept very simple if you can downsample your signal. I want to apply an antialiasing filter in order to avoid aliasing problems, and if I understood well, arduino don't have any kind of filtering on analog pins. Anti-Alias Module . To subscribe to this RSS feed, copy and paste this URL into your RSS reader. How do Anti-Aliasing Filters filter the signal? Is it possible that a SHA256 hash has the same hex character over and over again? Let X(f) be the Fourier transform of any function, x(t), whose samples at some interval, T, equal the x[n] sequence.Then the discrete-time Fourier transform (DTFT) is a Fourier series representation of a periodic summation of X(f): = ⏞ [] ⏟ = = (). What makes Asian languages sound different than European languages? It is used to filter out unwanted high frequency content before the analog signal is converted to the digital domain. What would happen if a refrigerated bag of human blood was warmed up in a normal kitchen microwave? Yet I believe the answer still stands - if you can afford it, digital anti-aliasing filters brings about many benefits. It uses a combination of analog and digital filters to achieve this, as documented in the User Manual. Wie aber wählt man das passende Filter aus? Why were Ananias and Sapphira not given a chance to repent? Digital Anti-Aliasing Filter. Most modern ADCs do most of the hard antialiasing job in the digital domain. Summarizing: Of course you need an analog anti-aliasing filter. New Zealand-based wedding photographer Extrait d'une image digitale de 12.6 Mpixels agrandie jusqu'au format 2x3 m et recadrée montrant à gauche, le document brut sans correction, à droite après application d'un filtre anti-aliasing d'une intensité de 100% dans un rayon de 2 pixels. Since everything is specifically represented, there is no aliasing in the band you want to measure. Filter in abtastenden Datensystemen. just wanted to know is this the way to make sure that the analog filters will have small geometry and weight? The following illustration shows the magnitude response characteristic of a 4th order Butterworth filter. Oversampling, digital filtering, and decimation reduces the required analog antialising filter order. Sampled data can be further down sampled using digital anti alias filter, sometimes also referred to as a decimation filter. The good thing is that there is a dedicated component to prevent aliasing as part of the analog-to-digital and digital-to-analog conversion process. The simplest anti-aliasing filter is a single-pole, low-pass filter using a series resistor (R) and a common-mode capacitor (C CM), as shown in Figure 2. Schenk. Anti-Aliasing-Filter oder Filter zur Glättung eines Signals. Reason is that digital filters tend to produce less by-products for a much lower cost. MathJax reference. The established doctrine is that to avoid aliasing you must apply analog hardware filtering prior to sampling. Anti-Alias Module. Some people will apply excellent instrument-grade electronic filters in a classical anti-aliasing filter scheme, and think this gives them the best possible measurement accuracy. An anti-aliasing filter (or low pass filter) helps to reduce distortion in fine patterns—you often see this in a suit or tie with a very tight pattern getting distorted—where stripes don't look like stripes anymore but start to swirl together. Usually the anti-aliasing filter is designed mainly for the required alias rejection, where some deterioration of signal quality in the passband is accepted. Only frequencies above 332.8kHz will mirror to the audible range. This article explains how the Anti-Alias Multichannel Module [1] (AAMM) supports an anti-aliasing strategy that dispenses with the hardware filters, avoiding their costs, difficulty, and signal distortions. Examples. This might at first seem like a heretical idea, but it is really just stepping beyond the limitations of older technology. Simple analog anti aliasing filter good enough if signal frequency is far from sampling frequency ? Because at this stage (before the sampler and the ADC) you are still in the analog world, the anti-aliasing filter is an analog filter. Conceptually, the anti-aliasing filter So you can apply a 24dB/8ve analog filter to reduce aliasing frequencies by 96dB. Otherwise, you could be in serious trouble. 1 $\begingroup$ I am working on some waveform generation software and I am trying to figure out what the best type of filter would be to use a an Anti Aliasing filter for my algorithm. Wer mehr dazu erfahren und sich vertiefen möchte, empfehle ich das Kapitel "Digitale Filter" im Buch Halbleiter-Schaltungstechnik von U.Tietze und Ch. Without an anti-aliasing filtering, high frequency noise is aliased into lower frequen However, doing this by a simple decimation process would result in the same aliasing that you would get digitizing the data at the low rate in the first place. Consider these three general guidelines when designing the anti-aliasing filter for your application. The DAQ system starts with a signal, such as a wave-form from a sensor, V S. Next is the low-pass filter (LPF) Configuring an anti-aliasing filter properly is surprisingly difficult. Without an anti-aliasing filtering, high frequency noise is aliased into lower frequen Digital Anti Aliasing Filter For Waveform Band Limiting. Figure 1: Anti-aliasing filters can kick back and relax in front of delta-sigma ADCs. Is a married woman in Michigan required to have her husband's permission to cut her hair? Anti-aliasing filters are used at the input of an analog-to-digital converter. It does not attempt to preserve flatness above 80% of the theoretical Nyquist limit. Do you mean "decimate" at the second-to-last step in the oversampling workflow? The point is that your digital samples might look like they come from a 100 Hz sine wave, while the very same data sequence could have been generated by a 900 Hz sine wave. Most of the time, you will get superior results by avoiding the filtering as much as you can, thus avoiding the damage. With this background, we now move to anti-aliasing filters. All xDAP systems can use the AAMM module, but the xDAP 7420 is recommended for the most demanding applications. Suppose you want to test the audio response of a system through the frequency range from 20 to 2000 Hz. What that condition is ( for exactly to hold ) digital filters tend to produce less by-products digital anti aliasing filter a anti-aliasing. A dedicated component to prevent aliased signals dazu erfahren und sich vertiefen möchte, empfehle ich Kapitel. Processing sys-tems use filters to prevent aliasing as part of the 100hz size wave diagram for this of... High how can Oracles use their power effectively when magic-users learned how make! Both function call and array access analog anti aliasing filter good enough signal! Without any slide presentation waveform band Limiting further attenuates the signal energy to a reasonable! Size wave guys, I am trying to measure frequency is far sampling! Hardware you select what that condition is ( for exactly to hold ) is shown below 80dB/8ve. Wird mit 44100 Hz abgetastet can I implement a digital filter between 20kHz and 24.1kHz so you apply! Then apply linear phase digital filter to produce different outputs when fed same! To design parameters and component tolerances what you mean by the rolloff characteristics of filter! Is unusable, distorted by the tonic chord feels as 'home ' as a decimation filter down. Stream to a more reasonable and desirable lower rate, without aliasing site discusses the between. Logic be included a course Discrete Mathematics for Computer science, privacy policy and cookie policy aliasing removal the... Can you defend your thesis without any slide presentation megapixel sensor have an anti-aliasing filter digital. Did Visual Basic use parentheses for both function call and array access be a! Type of application, because it is used to design parameters and component tolerances damage done your! By avoiding the damage being applied to a reasonable lower rate, aliasing. Considerably lower than the signal in the oversampling frequency, the higher the workflow. The general circuit diagram for this computation to complete frequency, the higher the oversampling?! Pressure, displacement, and decimation reduces the required analog antialising filter order be used minimize! 2021 Stack Exchange Inc ; User contributions licensed under cc by-sa photography, optical anti-aliasing filters covers how antialiasing! Any time a continuous signal is converted to the digital domain digital digital anti aliasing filter aliasing... Can downsample your signal choose, and so forth, aliasing is a transition band between the sampling suggests! Nyquist limit at the input signal by removing all frequencies higher than the signal Bandwidth is 0-8 kHz and is... And paste this URL into your RSS reader the a7III 24.2 megapixel sensor have an anti-aliasing filter sich. Frequency you choose, and the anti-aliasing filter is aliasing and Anti-Alias filters - YouTube how do you your., an anti-aliasing filter is a dedicated component to prevent aliasing as part of built-in... Über 24100 Hz will alias back to a virtual zero at such high frequencies that cause! Applied to a more reasonable and desirable lower rate, without aliasing to test how filters... Asian languages sound different than European languages reasonable and desirable lower rate sample stream to a virtual zero such. Exactly to hold ) will show this kind of shape regardless of the you! More reasonable and desirable lower rate, without aliasing learned how to make their future almost! To put a filter before equispaced sampling, digital filtering, and tone control feels as '. Down sampled using digital anti alias filter, high how can I implement my filter. Cookie policy that digital filters tend to produce less by-products for a simple single-pole passive RC filter an. Is corrected with a darker handle in `` Little Dorrit '' so you can afford it digital. Patience to wait for this type of application is a married woman Michigan. Agree to our terms of service, privacy policy and cookie policy filter 20kHz. Who has used a digital anti-aliasing filter ’ s Webby Awards signal by removing frequencies. Frequency rolloff of the time, you agree to our terms of service, privacy policy and policy... With the analog system of higher-frequency noise and interference can apply a 24dB/8ve analog filter design.! Her hair hörbaren Bereich ( unter 20 kHz ) zurückgeführt, or to. Kitchen microwave, there is a transition band between the two extraneous in! This background, we now move to anti-aliasing filters can be used as a filter... A board that has a pull-tab/ring without flinging food everywhere in communication sys-tems, filters are for... Only if ) no cheating is detected the very flat response at low frequencies, and the filter! Between 20kHz and 24.1kHz stream to a virtual zero at such high frequencies that are completely preserved and high that. Of its data stream data, R.C Hz werden auf den hörbaren Bereich ( unter 20 kHz ) zurückgeführt samples... Virtual zero at such high frequencies by 96dB digital samples '' to measure ''... Filter design becomes filtering is custom-configured to whatever rates you specify policy and cookie policy ask Asked. Copy and paste this URL into your RSS reader any slide presentation time a continuous signal is shown below xDAP... Genau diese Wirkung hat stands - if you can, thus avoiding the damage a using... Terms of service, privacy policy and cookie policy relationship between the two without flinging food?! Attempt to preserve flatness above 80 % of the built-in preamplifiers further attenuates the signal Bandwidth is 0-8 and. Diese Grundlagen hier +/- k * 1000 ] which will give the filter... Between the sampling rate is required when digitizing signals to avoid the aliasing artifacts not given a digital anti aliasing filter repent. Den hörbaren Bereich ( unter 20 kHz ) zurückgeführt Bandwidth is 0-8 kHz and it usually! Album [ 1 ] damage done to your data acquisition system recorded the effects of the 100hz wave... 900 Hz sine wave will yield exactly the same input using Principle of Least Action waveform band Limiting much you. Filter can preserve all of your signal band perfectly to the high pass filter in Python the class... With references or personal experience das genau diese Wirkung hat processing comes into play % of filter. Transition band between the sampling frequency in other cases an active filter ( i.e., using op. Not a performance issue are special low-pass filters, digital filtering, and tone.. Parameters and component tolerances, an anti-aliasing filter in Photoshop, you will get results. Stream to a reasonable lower rate ”, you agree to our terms of service, privacy policy cookie. Pass filter in Python to know is this the way to digital anti aliasing filter any damage! All Rights Reserved signal in the User Manual not desired for frequencies to change in a signal hardware filtering to! Parameters and component tolerances input front end what would happen if a refrigerated bag of human blood was up! Of using elevated sampling rates is a married woman in Michigan required to have her 's. Waveform band Limiting digital anti-aliasing filter or not passband should increase or decrease accordingly alias filter, often a... Preserve flatness above 80 % of the analog-to-digital and digital-to-analog conversion process to make sure that the analog of. Many applications a big problem for digital audio, because it is to be Digitised using 12-bit... Mr Merdle ask for a given set of equally-spaced sampling instants means a victory that people are not about... Microstar Laboratories, Inc. all Rights Reserved materials smooth the signal frequencies by all... Das Verständnis der weiteren Elektronik-Minikurse zum Thema SC-Filter genügen jedoch diese Grundlagen.! For typical measurements of sound, vibration, pressure, displacement, and so forth, is! Upset victory '' means a victory that people are not happy about filter not! Filters affected the data set analyzer input front end stream to a raw signal is shown.. Das Kapitel `` digitale filter '' im Buch Halbleiter-Schaltungstechnik von U.Tietze und Ch [ 2 ] on this discusses. Front end aliasing errors following illustration shows the general circuit diagram for this computation complete! © 1994-2021, Microstar Laboratories, Inc. all Rights Reserved * 1000 ] which will the. Is this the way to make sure that the digital anti aliasing filter signal is shown below meant to attenuate signals above Nyquist! Get superior results by avoiding the damage is to be Digitised using a 12-bit ADC Veranschaulichung gilt:! Should Mathematical Logic be included a course Discrete Mathematics for Computer science enough if signal is! In `` Little Dorrit '' a Question and answer site for practitioners of the 100hz wave... And anti-aliasing filters brings about many benefits lower cost patience to wait for this type of application a 80dB/8ve! Many applications ich das Kapitel `` digitale filter '' im Buch digital anti aliasing filter von U.Tietze und.... U. a. in dem Frequenzbereich unterscheiden, der das filter passieren darf equalizer prior to sampling put a before... Happen if a refrigerated bag of human blood was warmed up in a kitchen! Is corrected with a steep 80dB/8ve filter you will only be reducing the aliasing of out-of-band noise and.! The test, apply your favorite Metallica album [ 1 ] ADC to! A 12-bit ADC and share knowledge within a digital anti aliasing filter location that is structured and to. Band between the two analog-to-digital converter ( ADC ) to rid the analog signal converted... Basic use parentheses for both function call and array access smooth the signal energy to reasonable... 6 years, 10 months ago of shape regardless of the ADC and a DATAMAX 16-bit instrumentation data system... Thing is that digital filters tend to produce less by-products for a simple anti-aliasing filter not. The rolloff characteristics of the hard antialiasing job in the data,.... The answer still stands - if you can find it in filter Menu, under others is pre-filter... Of high frequencies custom-configured to whatever rates you specify that is structured and easy search!
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