Heritage Audio has announced an update to the classic Baxandall EQ, creating a “functional equivalent” to the Baxandall design, the Stereo Asymptotic Equaliser or “Symph EQ”. This is named after the shape of the shelf curves where the boost and cut amplitude grows up until the “asymptotic value” is reached, keeping the extreme highs and lows under control.

The sound is described as natural, with the use of parallel EQ helping with the phase response. The EQ features a high and low shelf with 10.5dB cut or boost and 6 frequencies for each shelf with 12dB/Oct high and low pass filters with a choice of 5 frequencies for each filter.

Heritage Audio highlights three features that really help this EQ perform.

• Carnhill Input transformers, the same ones as used in the Heritage Audio Successor.

• The outputs are driven by 73 style Class A output amplifiers with Carnhill/St Ives output transformers

• Built-in Mid/Side capabilities

What Is A Baxandall EQ?

The Baxandall filter design was first published in 1952. It was a hugely successful high and low shelf design that outperformed the prevailing passive networks which were common at the time through use of negative feedback. When implemented in hardware (plugin emulations weren’t common in the 50s) it has a distinct advantage in that it doesn’t involve the use of expensive rotary switches. This affordability and simplicity which made it hard to make it sound bad made very popular in HiFi equipment though Peter Baxandall, the designer, never received any royalties for the design.

The Baxandall shelf shapes are distinctive because the high shelf rises smoothly and very gradually, never quite flattening off into a shelf. This rise can be over as much as five octaves so this is a very broad brush EQ, progressively cutting or boosting more as frequency increases. The low shelf curve looks like a conventional shelf though it is still noticeably smooth. These two shelving filters, when combined with the 12dB/Oct high and low pass filters allow for some surprisingly detailed EQ work when used in combination.

The Symph EQ is available now and costs $1499/€1549. Find out more at Heritage Audio.