[6][nb 5] In April 1974, the resulting "RUSW-200" prototype first led to the development of a sliding two-band compander by Ernst F. Schröder of Telefunken Grundlagenlaboratorium, Hannover since July 1974.
However, the finally released High Com system, which was marketed by Telefunken since 1978, worked as a broadband 2:1:2 compander, achieving almost 15 dB of noise reduction for low[10] and up to 20 dB RMS A-weighted for higher frequencies,[19][3][10][15] reducing the noise power down to 1%[15] while avoiding most of the acoustic problems observed with other high compression broadband companders such as EMT/NoiseBX, Burwen [it] or dbx.
[15] With minimal changes in the external circuitry the IC could also be used to emulate a mostly Dolby B-compatible compander as in the DNR (Dynamic Noise Reduction) system[10] for backward compatibility.
However, it became apparent that a single-band compander without sliding-band technology, which was protected by Dolby patents, suffered too many audible artifacts.
[49][50][51][nb 12] A low-cost implementation of the Telefunken High Com system as external compander box became available as Hobby-Com,[20][15][52] developed by Telefunken product development[3] and Thomsen-Elektronik[20] for WDR, distributed by vgs [de],[20] and promoted for do-it-yourself assembly in the popular TV series Hobbythek [de] format by Jean Pütz on 7 February 1980.
High-Com II[nb 1] even required calibration of the playback level using a 400 Hz, 0 dB, 200 nWb/m[21] calibration tone for optimum results, and with prices in the several hundred dollars for the external Nakamichi compander box it was much too expensive to be used by many people outside the small group of audiophiles using high-end tape recorders or open-reel decks.