Audio pioneer Alan Blumlein’s idea of stereo sound, produced by two spaced loudspeakers, assumes that both speakers reproduce the same sound at the same time, and that the wave-fronts they produce differ only in amplitude, but not phase.

This ‘intensity stereo’ concept was detailed in Blumlein’s 1933 patent .

Sounds above 700hz from each speaker in a stereo setup, arrive from one slightly later than the other.

Consequently, each ear receives two sound waves that differ in intensity and phase because time delays in the room.

The two waves combine at the ear, where the perceived arrival time of the co-joined wave-front at one ear relative to the other, is decoded by the brain as spatial depth, as in real life. (humans use High frequency time delays to locate the source of a sound)

Most people find this illusion convincing, most of the time.

However the two-speaker arrangement only works accurately for frequencies below about 700Hz.

Above that and the listener’s head acts as a baffle between each ear, smearing the sound image.

Like a camera lens, where red and blue light refracts differently, blurring the sharpness of the overall picture at the film plane.

A similar thing happens with stereo loudspeakers where the high-frequency above 700hz are reproduced slightly wider than the low-frequency elements, blurring the focus of the stereo image.

EMI’s experiments confirmed this and a corrective device called the Stereosonic Shuffler was built into their in-house REDD mixing consoles employed throughout the ’50s and ’60s.

Inevitably complex large problematic and expensive, it was abandoned and ‘Stereosonic Shuffling’ fell out of favour,

‘uncorrected stereo’ (a fuzzy picture) was deemed ‘good enough’ for the consumer.

With the advent of CD there was a perception that something was missing! They just did not sound like vinyl records! Apart from the clicks pops and scratches,the imaging seemed to be lacking on certain recordings.

Well it was!

The mechanical and electrical crosstalk from the pick-up bouncing in the grooves at high-frequencies reduced the HF image width, producing Stereosonic Shuffling accidentally.

Since HF crosstalk had been deliberately engineered out of the CD’s, some form of image width correction remains desirable for digital replay formats.

No crosstalk = poor imaging!

Electronics whizz Richard Brice studied the problem and solved it, in miniature, for his Phd.,

The Francinstein Actif was designed and sold in small numbers back in the 1990’s and deliberately introduces a small amount of high frequency crosstalk from one side to the other to sharpen the stereo image.

There is a passive version, but this one has an active electronic buffer circuit to compensate for variance in source equipment impedances.

The passive version does not.

This is a VERY rare item, which I have never seen for sale second-hand since i bought it in the early 1990's from from Mr.Brice himself, and have had it ever since.

comes with DC power supply .

N.B. It is a purely analogue device, you run your digital feed into a DAC and take the analogue output through the Francinstein to your power amp where it samples the left and right signals and bleeds (crossfeeds) a specific amount of the high frequencies between the two channels, which depending on the recording and content, enhances the stereo effect of instruments with a high frequency content, i.e. Not a double Bass, or a low pipe on a church organ!!!