The Heritage Audio Stereo Asymptotic Equalizer, affectionately known as Symph EQ, takes its name from the shape obtained by its shelf curves; where the boost or cut amplitude grows up until the asymptotic value is reached, keeping the ultra highs and sub lows always controlled. Its sound can only be described as tight, sweet and natural, and its use of parallel equalizing to obtain the desired response curves makes it to have exceptional low phase deviation and artifacts. A smart circuit layout allows for a maximum boost/cut of 10.5 dB in 0.5 dB steps. The main rotary switch sets 1dB steps whilst the 0.5 button adds half a dB to the main reading. The CUT button turns the boost amount into cut. Six strategically selected frequency choices per band are available. In order to keep the sub-low and ultra-high frequency content well under control, further high-pass and low-pass filters have been added on dual concentric rotary switches, at 12dB/octave. Five frequency choices plus Off are available on each.