[Elecraft] Blue Tooth - Freq. response

[Jim Brown]

> Any multi-band EQ beyond two bands - e.g, other than simple high
> boost/cut and/or low boost/cut designs - must, by definition, be
> parametric.

Not quite.  From a user point of view, there are two types of multi-band 
equalizers -- graphic, and parametric. A graphic equalizer has filters 
that have a fixed bandwidth and are fixed in frequency. The only user 
control is to change the amount of boost or cut within that band. The TX 
and RX equalizers in the K3 are graphic equalizers.

A parametric equalizer has filters that can be varied in frequency, 
bandwidth, and amount of boost or cut.

A shelving equalizer is one that transitions from flat response in the 
midrange to either boost or cut (usually cut) on the low end and/or the 
high end. In that "cut" region" the response is also flat, thus the name 
"shelf." The transition from flat to boost or cut is a gradual one, the 
shape of that transition and the degree of boost or cut can be varied by 
design of the analog circuit or the DSP that simulates the analog 
circuit, and that shape affects the sound quality.

A high pass or low pass filter differs from a shelving equalizer in that 
it is only capable of cutting (rolling off) the response above or below 
the desired frequency limit, and that there is no intentional "shelf" -- 
that is, the gain in the cut region keeps dropping as you move away from 
from the frequency limit.

All of these types of equalizers can be implemented with analog 
components, or in DSP that simulates those analog components.  The K3 
uses high pass and low pass filters and shelving EQ, implemented in DSP, 
to limit the bandwidth of the system.

In the audio world, most products called parametric equalizers also 
include high pass, low pass, and shelving functionality.  Nowadays, 
virtually all modern products are implemented in DSP. Before the days of 
DSP, parametric equalizers were used, but graphic equalizers (mostly 10 
bands or 27 bands) dominated the market because they were easier to 
understand, and easier to set without getting into trouble.  DSP and 
modern instrumentation (and display of the response) changed all that -- 
every filter burns processing power, so a 27-band equalizer required 5 
times the DSP of a 5 band parametric, and the modern 
instrumentation/display made it easier to see what you were doing with 
the equalizer.  TXEQ and RXEQ in the K3 is a well thought out compromise 
between processing power and simplicity of use that does almost anything 
an intelligent user might need.

73, Jim Brown K9YC