Minidisc was a promising format when it was introduced in the 1990s but ultimately the convenience of file formats like MP3 that allowed computer (and phone!) playback and unlimited copying sealed minidisc’s fate. The record industry was going through an existential crisis at the time and felt it had to protect itself in any & every way possible against any digital media that allowed unlimited copying. In the minidisc world Sony (as music label owner as well as equipment vendor) had a vested interest in enforcing the standards for controlling how many digital copies consumers could make of their music on minidisc with SCMS (Serial Copy Management System). A digital copy from CD to MD would have the SCMS bits set so that no further digital copies could be made. Professional audio gear didn’t have these restrictions however. The problem with SCMS was its blanket application – it would stop copying regardless of whether copyright was involved or not… users were prohibited from copying their own or non-copyrighted audio.
Elektor, an electronics magazine, published details in 1998 of a kit that had been designed to modify the SCMS data (actually set copy protection to “unrestricted”) in the S/PDIF digital audio signal on the fly so that all restrictions on further digital copies were removed (actually published earlier in Dec 1997 in German/Dutch issues of the magazine). The so-called “copybit killer”. The design used a novel approach using a handful of widely available standard chips (no specialist audio devices required) and the data matching/stripping was handled by a finite state-machine (“FSM”) realised with shift registers + ROM. It’s a handy piece of kit that also doubles as an optical/electrical format converter. The kit was available from “Stippler Elektronik” in Germany – either fully assembled or as components + PCB.
I purchased the kit of components + PCB in January 2000 from Stippler and assembled it shortly after. I recently found the original order which I had sent over to Germany by Fax 🙂 (back then it was 126DEM, or around 64EUR and with postage it cost me just under 50GBP)
There were all sorts of other ways around SCMS for users with consumer-grade equipment – like recording to or from PC via S/PDIF enabled sound card but MD-deck to MD-deck copying at the time was always problematic on consumer-grade machines.
The company that produced the kit, Stippler Elektronik, has since disappeared. Unfortunately the binary contents of the 27C512 EPROM are not available anywhere. The original Elektor article refers to a Pascal programme used to create the binary file but doesn’t offer a listing or any other details apart from saying that “the pre-programmed ROM is available from suppliers”. The design was attributed to “H Hanft” (actually Dipl.-Ing. Hans-Juergen Hanft) – if you’re still around, or indeed if anyone anywhere has another ROM to compare contents with please get in touch 🙂 Maybe Georg Stippler knows? The programmed ROM is known by its part number “EPS 976516-1” and the whole kit is 970069 or E970069.
(UPDATE [2021-02-22]: thanks to some very clever people over at the SonyInsider forum who have reverse-engineered the ROM contents from the FSM schematic & S/PDIF specification we now have C, Python & Tcl code that can re-generate the binary image of the ROM 😀 )
(UPDATE around late May/early June 2021 the SonyInsider forums went offline for some weeks – the link above should take you to a waybackmachine archive 😦
here’s the original: http://forums.sonyinsider.com/topic/30611-elektor-copybit-stripper/)
Title: Einfacher Copybit-Eliminator: Digitales Kopieren ohne Beschraenkungen
In: ELEKTOR -GANGELT THEN AACHEN-; 324; 30-38
Year of publication: 1997
Publisher: ELEKTUUR B.V.; –
Document Type: Article (Journal)
Type of Material: Print –
Language: German –
Database provider: Technische Informationsbibliothek (TIB)–
Database name: TIB-Portal