Elliptic Equalizer Comparison
Posted: Mon May 12, 2014 2:18 pm
I had a chance to revisit the subject of elliptical equalizers to provide low frequency crossover to mono for vinyl mastering, improved ear-bud/headphone listening and improved small-speaker and subwoofer performance.
My working theory is that the steering of side information to the opposing channel used in the original Neumann VAB-84 is superior to the subtractive method used in the EE-70, EE-77 and simple L+R methods to derive Mono at low frequencies.
The original VAB-84 had a sliding -6dB/Octave filter. In its original application, Direct Metal Mastering, the sliding filter made sense.
It was discovered however that the steering technology used in the VAB-84 permits higher-order filters making a sliding filter unnecessary.
The "EE-84" (my shorthand for a VAB-84 elliptical equalizer) uses a fixed frequency filter with either 12 or 18 dB per octave slope.
This a crosstalk comparison curve showing a "subtractive" EE-70 (emulated) -6dB response versus a -12dB and -18dB per octave filters in a "steering" "EE-84" (VAB-84 but higher-order) configuration.
Crosstalk Curves
EE-77 subtractive vs. EE-84 steering mono crossover comparison.
Reference level was approx -5dB full scale.
When crossover to mono occurs, the signal is split equally between channels.
Thus, the response converges to approx -12 dB FS.
The mono sum for the "EE-84" (high-order VAB-84 emulator) is always unity.
There is no "phase hole" in mono.
The higher filter orders of the "EE-84" do not compromise mid range imaging and sound far more transparent than does the EE-77.
My working theory is that the steering of side information to the opposing channel used in the original Neumann VAB-84 is superior to the subtractive method used in the EE-70, EE-77 and simple L+R methods to derive Mono at low frequencies.
The original VAB-84 had a sliding -6dB/Octave filter. In its original application, Direct Metal Mastering, the sliding filter made sense.
It was discovered however that the steering technology used in the VAB-84 permits higher-order filters making a sliding filter unnecessary.
The "EE-84" (my shorthand for a VAB-84 elliptical equalizer) uses a fixed frequency filter with either 12 or 18 dB per octave slope.
This a crosstalk comparison curve showing a "subtractive" EE-70 (emulated) -6dB response versus a -12dB and -18dB per octave filters in a "steering" "EE-84" (VAB-84 but higher-order) configuration.
Crosstalk Curves
EE-77 subtractive vs. EE-84 steering mono crossover comparison.
Reference level was approx -5dB full scale.
When crossover to mono occurs, the signal is split equally between channels.
Thus, the response converges to approx -12 dB FS.
The mono sum for the "EE-84" (high-order VAB-84 emulator) is always unity.
There is no "phase hole" in mono.
The higher filter orders of the "EE-84" do not compromise mid range imaging and sound far more transparent than does the EE-77.