Changed Digital Fltration to Digital Filtering to reflect common usage - searching for 'digital filtering' gives the digital filter article as the first hit,; 'digital filtration' does not
A very useful real application that demonstrates this idea was the development of impulse response [[loudspeaker]] testing in the 1980s which led to big improvements in loudspeaker design. Loudspeakers suffer from [[colouration]], a defect that has nothing to do with theunlike normal measured properties like [[frequency response]]. because itColouration is thecaused result ofby small delayed sounds that are the result of resonance, or energy storage in the cone, the internal volume, or the enclosure panels vibrating. TheseColouration 'smearsmears' the sound,givingwhich reducedreduces the 'clarity' orand 'transparency.' to the sound. Measuring the impulse response, which is a direct plot of this '[[time-smearing]]' provided a tool for use in reducing resonances by the use of improved materials for cones and enclosures. Initially, short pulses were used, but the need to limit their amplitude to maintain the linearity of the system meant that the resulting output was very small and hard to distinguish from the [[noise]]. Later techniques therefore moved towards the use of other types of input, like [[maximal length sequence]]s, and using computer processing to derive the impulse response. Recently this has led to the very graphic three dimensionalgraphical [[waterfall plotspectrogram]]s plots that can often be seen in test reviews, ofshow delayed response shown against time for each frequency.
=== Digital filtering ===
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=== Electronic processing ===
Impulse response analysis is a major facet of [[radar]], [[ultrasound imaging]], and many areas of [[electronicdigital signal processing]]. An interesting example would be [[broadband]] internet connections. Where once it was only possible to get 4 kHz speech signal over a local telephone wire, or data at 300 bit/s using a modem, it is now commonplace to pass 2 Mb/s over these same wires, largely because of '[[Adaptive filter|adaptive equalisation]]' which processes out the time smearing and echoes on the line.
