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One of the nice things about the Cambridge EQ is the large selection of filter types for its low and high pass filter sections. It also provides a good opportunity to compare how these types affect the audio, particularly at or near the cutoff frequency.

The plots here are made with a 4600 Hz sine wave that has significant level changes. The signal is put through each filter type, (high-passed at 4150 Hz) and bounced in realtime. This shows how the filter responds to changes in level, and how each filter affects the overall level of the signal near the cutoff.  This helps to understand how EQ filter "ringing" has an effect in a more "real world" example. The filter performance shown here is actually "pretty darn good". 

I've also noted the phase shift at the cutoff frequency for each filter type. Note that these plots are to show what happens "near" the cutoff. Things improve alot the further up (away) from the cutoff frequency you measure.  The phase measurements here are very typical for EQ low or high-pass filters that are non-linear phase, which is actually "standard" phase, or what the marketing people like to call "minimum" phase.

Test signal is 4600Hz.

All phase shifts are noted for 4150Hz.

Reference Signal:

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