Elecraft KDSP2 Manual - Manual (Page 47)

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DSP
Digital Signal Processing. This is a system that accepts signals that are digitized, and performs operations
on them, such as filtering. In the context of most Amateur radio equipment, the term DSP often applies to
the whole accessory, like the KDSP2, and is taken to include the analog-to-digital and digital-to-analog
conversions as well.
FIR
Finite impulse response. This is a basic filter structure which does not use feedback. As a result, it cannot
oscillate. FIR filters are common in DSP work, but very rare in analog design. FIR filters usually need
much greater length to get similar results to an IIR filter, but FIR filters are often much better behaved.
They have controlled phase characteristics, less ringing, and so forth.
In the KDSP2, all filters are FIR filters.
See also IIR.
Gain
This indicates the amount of amplification, or attenuation, of a signal. In the KDSP2, various GAIN menus
are available. Their purpose is not to increase the gain of the overall K2 system. Rather, they are provided
to balance the gain between the various modes and functions. For example, assume you have SSB Gain set
to 4.5, CW gain to 3 .0 and RTTY gain to 5.0. They should all be reduced by 3.0. This will result in
settings of 1.5, 0.0 and 2.0, respectively. When doing gain balancing, one of the gains should be 0.0. The
Sn and Cn menus are to accommodate a possible loss of signal strength when the denoiser is active.
IIR
Infinite impulse response. This is a basic filter structure which uses feedback. As a result, it can oscillate
and ring. Nearly all op-amp and switched-capacitor filters in common use are IIR. Some DSP filters are
IIR, as these filters require far less computation for a given response. IIR filters often cannot provide
desired phase and amplitude response characteristics, and are only used in DSP systems in certain special
cases.
The KDSP2 does not use IIR filters.
See also FIR.
Interpolation
This is a process where a signal that was sampled at a lower rate is made to appear as if it were sampled at
a higher rate. In the KDSP2, the autonotch and denoiser operate at a 16 kHz rate, but the filter that
precedes them is running at 8 kHz. An “interpolate by two” operation is used to convert the lower
sampling rate to the higher one.