Editing Digital filter (section)

==Comparison of analog and digital filters==
Digital filters are not subject to the component tolerances, temperature variations, and non-linearities that greatly complicate the design of analog filters. Analog filters consist of imperfect electronic components, whose values may also change with temperature and drift with time. As the order of an analog filter increases, and thus its component count, the effect of variable component errors is greatly magnified. In digital filters, the coefficient values are stored in computer memory, making them far more stable and predictable.<ref name="dspguide">{{cite web | url=http://www.dspguide.com/ch21/1.htm | title=Match #1: Analog vs. Digital Filters }}</ref>

Because the coefficients of digital filters are definite, they can be used to achieve much more complex and selective designs &ndash; specifically with digital filters, one can achieve a lower passband ripple, faster transition, and higher stopband attenuation than is practical with analog filters. Even if the design could be achieved using analog filters, the engineering cost of designing an equivalent digital filter would likely be much lower. Furthermore, one can readily modify the coefficients of a digital filter to make an [[adaptive filter]] or a user-controllable parametric filter. While these techniques are possible in an analog filter, they are again considerably more difficult.

Digital filters can be used in the design of finite impulse response filters which can achieve extremely steep rolloff slopes with no phase shift. Analog filters that perform the same function are often significantly more complicated, as they would require many delay elements.

Digital filters rely less on analog circuitry, potentially allowing for a better [[signal-to-noise ratio]]. A digital filter will introduce noise to a signal during analog low pass filtering, analog to digital conversion, digital to analog conversion and may introduce digital noise due to quantization. With analog filters, every component is a source of thermal noise (such as [[Johnson noise]]), so as the filter complexity grows, so does the noise.

However, digital filters do introduce a higher fundamental latency to the system. In an analog filter, latency is often negligible; strictly speaking it is the time for an electrical signal to propagate through the filter circuit. In digital systems, latency is introduced not only by delay elements in the digital signal path, but also by [[analog-to-digital]] and [[digital-to-analog converter]]s that are required for a system to process analog signals. Digital filters must also deal with quantization and rounding errors, and often have much less headroom than analog filters, since most DSP ICs operate on only 5V or 3.3V while operational amplifiers typically operate on 12 to 24V.

Additionally, in very simple cases or in cases where frequencies and filter slopes are fixed, it is more cost effective to use an analog filter. Introducing a digital filter requires considerable overhead circuitry, as previously discussed, including two low pass analog filters. Analog filters also require substantially less power than digital filters and are therefore the only solution when power requirements are tight.

When making an electrical circuit on a [[Printed circuit board|PCB]] it is generally easier to use a digital solution, because the processing units are highly optimized over the years. Making the same circuit with analog components would take up a lot more space when using [[discrete component]]s. Two alternatives are [[Field-programmable analog array|FPAAs]]<ref name=FPAA>{{cite journal|last=Bains|first=Sunny|title=Analog's answer to FPGA opens field to masses|journal=EETimes|date=July 2008|url=http://www.eetimes.com/document.asp?doc_id=1167814}}</ref> and [[ASICs]], but they are expensive for low quantities.