Minidisc copybit stripper – the Elektor SCMS killer

Minidisc was a promising format when it was introduced in the 1990s but ultimately the convenience of file formats like MP3 that allowed computer-based (and ultimately smartphone!) 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 digital media that allowed unrestricted copying. In the minidisc world Sony (as both music label owner and as equipment vendor) had some vested interest in enforcing the standards for controlling how many digital copies consumers could make 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 on “consumer” grade recorders however professional audio gear didn’t have any of these restrictions. The problem with SCMS was its blanket application – it would stop digital copying regardless of whether copyright was involved or not… users were prohibited from digitally copying their own or other non-copyrighted audio.

Elektor, an electronics magazine, published details in 1998 of a kit that had been designed to modify the SCMS data (set copy protection to “Permitted”) in the S/PDIF digital audio signal on the fly so that all restrictions on further digital copies were removed (originally 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 expensive/rare 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)

Utilising the well-known anti-static properties of a cardboard album cover as anti-static mat 🙂

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) The programmed ROM is known by its part number “976516-1” or “EPS 976516-1” or “Elektor-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 – available for download below 😀

UPDATE [May/June 2021] the SonyInsider forums went offline for some weeks – here’s a link to a waybackmachine archive :

UPDATE [June 2022] another ROM found in the wild and imaged: )

Title: Einfacher Copybit-Eliminator: Digitales Kopieren ohne Beschraenkungen
Year of publication: 1997
Publisher: ELEKTUUR B.V.;ISSN: 0932-5468
Document Type: Article (Journal)
Type of Material: PrintLanguage: GermanClassification:DDC: 621.3
Database provider: Technische Informationsbibliothek (TIB)Database name: TIB-Portal

Generating the ROM contents on Android using QPython 3L 😎

Published by zedstarr

Chilled out human being, doing techy stuff.

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