[25][26][27][28] It is based on the High Select tracking filter (German: Mitlauffilter aka MLF) developed by Jens Hansen since 1982.
[25] A very similar technology is the Active Real-time Tracing System (ARTS), as was implemented in the Pioneer Elite F-91 and some versions of the F-717[nb 5] high-end tuners in 1987.
[29][30][31][32][33] Super Sound Tracing (SST) is a similar technology by Sony affecting the RF rather than the IF stage.
[45][36][nb 6] Blaupunkt's Sharx technology, as introduced in 1997 in the Modena & Lausanne RD 148 car radios with "DigiCeiver", is a similar digital solution implemented in software.
The original Sharx implementation still relied on a bank of switchable analog ceramic resonators for the IF filter stage before the A/D conversion for further processing of the signal in the DSP section.