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	PWM LPF paper by WB6BLD (Site not responding. Last check: 2007-10-08)
		This post-modulator lowpass filter should not be used as the primary transmission-bandwidth-limiting filter; that function is done more effectively by a sharper-cutoff lowpass filter employed in the lower-level audio processing stages.
		The load on the output of the filter is typically 5 to 25 ohms for a solid-state transmitter or perhaps 1000 to 5000 ohms for a vacuum-tube transmitter.
		It may be found during exploration of the design phase of the post-modulator lowpass filter that the design may be improved in one or more areas by using as a final element a shunt capacitor which is smaller than the design of the RF system dictates.
	mywebpages.comcast.net /tonne/appnotes/pwm/pwmham.html (4274 words)

	Digital Filters - Frequency Filters
		The result in the spatial domain is equivalent to that of a smoothing filter; as the blocked high frequencies correspond to sharp intensity changes, i.e.
		We obtain the filter function of a bandpass by multiplying the filter functions of a lowpass and of a highpass in the frequency domain, where the cut-off frequency of the lowpass is higher than that of the highpass.
		To perform the frequency filtering we transform both the image of the house and the mask into the Fourier domain where we multiply the two images with the effect that the frequencies occurring in the mask remain in the output while the others are set to zero.
	homepages.inf.ed.ac.uk /rbf/HIPR2/freqfilt.htm (2854 words)

	Lowpass Filter Design
		From the graphical method for visualizing the amplitude response (§8.1), we see that this filter totally rejects signal energy at half the sampling rate, while lower frequencies experience higher gains, reaching a maximum at
		While it is impossible to achieve this ideal response exactly using a finite-order filter, we can come arbitrarily close.
		These generally yield IIR filters with the same number of poles as zeros.
	www-ccrma.stanford.edu /~jos/filters/Lowpass_Filter_Design.html (209 words)

	allpasslp2hp (Filter Design Toolbox)
		Choice of the feature subject to the lowpass to highpass transformation is not restricted to the cutoff frequency of an original lowpass filter.
		Lowpass to highpass transformation can also be used for transforming other types of filters; e.g., notch filters or resonators can change their position in a simple way by using the lowpass to highpass transformation.
		Design the allpass filter changing the lowpass filter to the highpass filter with its cutoff frequency moved from
	www.weizmann.ac.il /matlab/toolbox/filterdesign/allpasslp2hp.html (336 words)

	EDN Access--04.10.97 Notch filter uses only lowpass filters (Site not responding. Last check: 2007-10-08)
		This scheme involves subtracting the lowpass filter’s output from the input data, and the total frequency response of the system is highpass.
		This scheme ensures that the frequency responses of the highpass and lowpass filters are mirror-symmetric.
		When the phase of the lowpass filter is not zero, you must compensate for the phase shift that this filter introduces into the datapath.
	www.edn.com /archives/1997/041097/08di_03.htm (440 words)

	Analog Filter Design Demystified - Maxim/Dallas
		To ensure conformance with the generic filter described by Equation 1, and to ensure that the last term equals unity, the first two quadratics have been multiplied by a constant.
		A 5th-order, 1dB-ripple Chebyshev lowpass filter is constructed from two non-identical 2nd-order sections and an output RC network.
		Bandpass and bandstop filters can also be implemented (with single op amps) using techniques similar to those shown, but those applications are beyond the scope of this article.
	www.maxim-ic.com /appnotes.cfm/appnote_number/1795 (2219 words)

	FIR Filter Design by Windowing (Site not responding. Last check: 2007-10-08)
		The window method begins with an ideal lowpass filter, whose impulse response is of infinite duration, and truncates it, producing a finite impulse response.
		The magnitude of the filter's frequency response is shown in the second plot.
		The impulse response of the shifted ideal lowpass filter is shown in the third.
	web.mit.edu /6.555/www/fir.html (317 words)

	54 MHz Lowpass Filter
		A transmitter low pass filter design project was started with goals of low insertion loss, broad SWR bandwidth, mechanical simplicity, easy construction, and operation on all HF amateur bands including six-meters.
		This filter is useful in reducing harmonic radiation in the VHF and higher frequency bands, and is made at home with low cost commonly available parts.
		If you wish to use this filter on the HF amateur bands from 1.8 to 30 MHz only, the adjustable tuning capacitor adjustment is not critical at all, and does not affect HF SWR performance.
	www.realhamradio.com /DC_54_mhz_lowpass_filter.htm (2866 words)

	SFSU Engineering 451 - Laboratory #5 - Lowpass filter design for upsampler and downsampler (Site not responding. Last check: 2007-10-08)
		While we will study FIR filter design in detail later in the term, for now all we need to do is to implement this filter using the procedure outlined in the book.
		The filter is specified to have a passband, 0
		The transition band of the filter, dw, is the frequency range over which the frequency response makes the transition between the passband and the stopband.
	robotics.eecs.berkeley.edu /~rvidal/engr451/FilterDesign.html (415 words)

	Filter types (Site not responding. Last check: 2007-10-08)
		In general a filter is a device that discriminates, according to one or more attributes at its input, what passes through it.
		One example is the colour filter which absorbs light at certain wavelengths.
		It is customary to classify filters according to their frequency domain charachteristics.
	cnx.rice.edu /content/m11868/latest (306 words)

	Lowpass Filter Has Improved Step Response - Maxim/Dallas
		Adding optimization circuitry to a lowpass filter allows the filter to adjust its cutoff frequency dynamically, preserving the step-response time for relatively low cutoff frequencies.
		A common problem when designing lowpass filters for signal conditioning is their effect on the system's time-domain response.
		This lowpass filter maintains a fast step response by dynamically adjusting its cutoff frequency.
	www.maxim-ic.com /appnotes.cfm?an_pk=3203 (481 words)

	:::::: MOOG MUSIC ::::::
		The award-winning MF-101 Lowpass Filter is a direct descendant of the original Moog modular synthesizers.
		All of the Lowpass Filter's parameters can be controlled with expression pedals or external control voltages as well as by great feeling knobs which beg to be tweaked.
		The MF-101 Lowpass Filter does the same sort of thing to the sound spectrum with it's Cutoff Control.
	www.moogmusic.com /detail.php?main_product_id=5 (401 words)

	Image Enhancement: Frequency-Domain Methods
		An ideal lowpass filter cuts off all frequencies greater than the cutoff frequency and passes perfectly all frequencies less than the cutoff frequency.
		What causes the ringing of ideal lowpass filters is the sharp cutoff in the frequency domain.
		Notice that the ideal highpass filter is identical to the ideal lowpass filter, with only a change in the direction of the inequality.
	rivit.cs.byu.edu /morse/550-F95/node18.html (748 words)

	Lowpass filter uses only two values - 7/5/2001 - EDN (Site not responding. Last check: 2007-10-08)
		The design technique is also applicable to highpass and wideband filters (references 3 and 4).
		The filter uses four inductors of two different values and five capacitors of two different values.
		We constructed the filter on Vector board in a die-cast aluminum enclosure with BNC input and output connectors.
	www.edn.com /article/CA90759.html (450 words)

	zpklp2mb (Filter Design Toolbox)
		In the second case the DC feature is kept at an original frequency and the Nyquist feature is allowed to move.
		Choice of the feature subject to this transformation is not restricted to the cutoff frequency of an original lowpass filter.
		This transformation can also be used for transforming other types of filters; e.g., notch filters or resonators can be easily replicated at a number of required frequency locations.
	www.weizmann.ac.il /matlab/toolbox/filterdesign/zpklp2mb.html (441 words)

	GameDev.net - Resonant Lowpass Filter Soruce
		The overall filter Q is a product of all * 2nd order stages.
		For example, the 6th order filter * (3 stages, or biquads) with individual Q of 2 will * have filter Q = 2 * 2 * 2 = 8.
		initially set to 1 * and modified by each biquad section in such * a way, as to make it the coefficient by * which to multiply the overall filter gain * in order to achieve a desired overall filter gain, * specified in initial value of k.
	www.gamedev.net /reference/articles/article845.asp (750 words)

	BesserBits (Site not responding. Last check: 2007-10-08)
		Using this method, an individual with no prior filter design experience can design a low-pass filter to his or her specifications in a short matter of time.
		For example, the Butterworth filter has a smooth passband response and more gradual out-of-band attenuation, whereas the Chebyshev filter has a "rippled" passband response and a steeper out-of-band attenuation.
		Then, tables or formulas list the element values that will produce a lowpass filter of that order with a cutoff frequency of 1 radian/second, with source and load terminations of 1 Ohm connected to it.
	www.bessernet.com /articles/lowpfilt/bwfiltstep00.html (335 words)

	[No title]
		The usual scenario where filtering is needed is when a noise EMBED Equation is added to a signal, but the noise has most of its energy at frequencies outside of the bandwidth of the signal.
		Approximations to the ideal lowpass filter that can be realized by causal LTI differential equations have been proposed in the past, and some of them have found widespread use.
		Notice that the frequency response of an ideal highpass filter can be written as the difference between 1 and the frequency response of an ideal lowpass filter.
	www.cim.mcgill.ca /~boulet/304-303B/1999/L19w97.doc (1148 words)

	iirlp2mbc (Filter Design Toolbox) (Site not responding. Last check: 2007-10-08)
		The prototype lowpass filter is given with a numerator specified by
		Frequency value to be transformed from the prototype filter.
		It should be normalized to be between 0 and 1, with 1 corresponding to half the sample rate.
	www.eas.purdue.edu /matlab/toolbox/filterdesign/iirlp2mbc.html (348 words)

	Hydrogenaudio Forums -> lowpass filter
		As I(painfully) learned, if you put the lowpass too high, instead of using bits on stuff you can hear, it uses them on stuff only your dog can.
		...so if you don’t use the lowpass filter, there’s going to be a lot of wasted bits there.
		I would guess that since the typical FM broadcast low pass filters at about 16kHz that it would suffice for many people.
	www.hydrogenaudio.org /forums/index.php?showtopic=5822 (1513 words)

	Fourier Space Smoothing Methods (Site not responding. Last check: 2007-10-08)
		The simplest sort of filter to use is an ideal lowpass filter, which in one dimension appears as shown in Fig.
		The problem with this filter is that as well as the noise, edges (places of rapid transition from light to dark) also significantly contribute to the high frequency components.
		Another filter sometimes used is the Butterworth lowpass filter.
	homepages.inf.ed.ac.uk /rbf/CVonline/LOCAL_COPIES/MARSHALL/node22.html (272 words)

	Lowpass FIR Filter Design (Site not responding. Last check: 2007-10-08)
		Our first example, "lowpass.sfs" does the job of making a CD sound like a telephone by using a lowpass filter.
		The frequency reponse plot shows that the filter is slightly better than required, because its response is between the lines showing the specified passband ripple, and below the line showing the minimum stopband attenuation.
		Going back to the Specification Editor for a moment, we can read numerical values of the filter's actual ripple and attenuation, which are "2.302" and "42.255".
	www.iowegian.com /lowpass.htm (373 words)

	Hydrogenaudio Forums -> Lowpass filter not used?
		I set it at q6 lowpass 20000 KHz(I would've set it at 19.5 but it's more efficient than MP3 so I said what the heck I'll try it, it's better than it cutting off at 22000 KHz), and I get great results.
		His post here wasn't at all that bad that it deserves again so harsh comments, although there will probably not be very much bitsavings by using using 20khz lowpass with -q6.
		BTW: CD audio is not supposed to have content beyond 20khz, or at least it is recommended to lowpass audio at 20khz in the mastering process.
	www.hydrogenaudio.org /forums/index.php?showtopic=5827 (1158 words)

	Synthesis Technology - MOTM-440 Discrete OTA Voltage-Controlled Lowpass Filter with VC Resonance
		You have probably heard of the SSM2040 filter chip, used in the Prophet 5 Rev. 2 synth, the Voyetra 8, and others.
		Although short-lived, the SSM2040 filter had a unique sound different from a Moog, ARP or other 4-pole lowpass.
		The internal gain structure is such that over-driving the filter is now possible (unlike the Prophet 5) to get even more nasty sounds.
	www.synthtech.com /motm440.html (249 words)

	iirlp2mb (Filter Design Toolbox) (Site not responding. Last check: 2007-10-08)
		Transform an IIR real lowpass filter to an IIR real M-band filter frequency response
		In the second case the DC feature is kept at an original frequency and the Nyquist feature is movable.
		Verify the result by comparing the prototype filter with target filters:
	www.eas.purdue.edu /matlab/toolbox/filterdesign/iirlp2mb.html (480 words)

	Sigma-Delta Modulation into Butterworth Filter versus Ideal Lowpass Filter (Site not responding. Last check: 2007-10-08)
		The output of the filter should be the original sine wave.
		of delta pulses and enters the lowpass filter.
		the Butterworth filter resembles the analog sine wave.
	www.dsprelated.com /showmessage/731/1.php (1566 words)

	[music-dsp] lowpass filter questions (Site not responding. Last check: 2007-10-08)
		Anything input to a digital filter shall have the right sampling rate.
		Taking the average is equivalent to filtering with a 4th-order FIR lowpass filter then downsampling.
		Yet this FIR filter is not necessary since you're already using an IIR filter, and the downsampling alters the sampling rate, causing trouble to your IIR filter.
	shoko.calarts.edu /pipermail/music-dsp/2004-September/028170.html (150 words)

	Analog Input Lowpass Filtering with an SCB-68 Terminal Block - KnowledgeBase - Support - National Instruments
		Solution: Soldering pads are provided on the SCB-68 to build RC lowpass filter circuits for the analog input channels.
		Note: Filtering increases the settling time of the instrumentation amplifier to the time constant of the filter used.
		Adding RC filters when scanning channels greatly reduces the practical scanning rate since the instrumentation amplifier settling time can be increased to 10T or longer, where T = (R)(C).
	digital.ni.com /public.nsf/allkb/5D82A2990FB1D21386256EEE00018FF0 (281 words)

	[music-dsp] newbie question about RBJ Lowpass Filter (Site not responding. Last check: 2007-10-08)
		Direct form I filters (all the ones in the RBJ) are unstable at high resonance.
		Use a ladder (moog) or svf (state variable filter) instead with a non linearity in the feedback section.
		When I swept > the filter cutoff with high resonance, the self oscillation only happened at > the > tiny end of sweep (at low cutoff).
	shoko.calarts.edu /pipermail/music-dsp/2002-June/016294.html (217 words)

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