Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rochester!pt!unh.cs.cmu.edu!agn From: agn@unh.cs.cmu.edu (Andreas Nowatzyk) Newsgroups: sci.electronics Subject: Re: 3800 Hz notch filter [will] be used on CD masters Message-ID: <1007@unh.cs.cmu.edu> Date: Fri, 26-Jun-87 01:51:22 EDT Article-I.D.: unh.1007 Posted: Fri Jun 26 01:51:22 1987 Date-Received: Sun, 5-Jul-87 19:53:01 EDT References: <598@neoucom.UUCP> <67@sdeggo.UUCP> <1597@ihuxi.ATT.COM> Organization: Carnegie-Mellon University, CS/RI Lines: 49 Keywords: with possible icky results! > Sorry, but the protection circuit will be buried deep in one of the LSI's. > There will be no way to remove it and even if you could, the notch will > still be there on the source CD. That is what has everyone so up in arms. It seems very unlikely that the copy-protection circuitry will be burried deep inside. Consider the nature of that chip: several filters, various integrators, gain-control, etc. (The block diagram was recently published in an audio magazin). This can be implemented either as an switched-capacitor device (a) or as a completely digital circuit (a). The process for (a) is incompatible with a controller micro used to control the entire DAT. (b) is fairly complex, requires a more difficult interface to get the digital data stream (that isn't available on the controller: the extra data-path may not live long... :-) and needs a substantial ammount of fast logic. Again, this is different from the usual low speed, low power process that is used for the controller. Besides, both approaches require significant silicon real estate and extra design efford to integrate this gadget in other circuitry (mostly standardized stuff). The larger chip has a lower yield, longer design time and is more difficult to test. The DAT controller (user interface, display, tape counter, remote controll, lots of other boring stuff - but no audio data handling) is a unlikely place for the CP stuff. Similar arguments can be made against placing the CP circuitry in parts of the recorder data-path. Note that there are at least 3 chips involved here: 1) ADC (perhaps with an integrated digital filter), 2) Digital data path (fifo, generation of EDC codes, adding control info, formatting) and 3) Driver (converts the digital data into an analog signal to drive the write head, various servo-loops, etc.) The technology for these essential parts are quite different (1: precision CMOS with some analog capabilities, isolated from the noisy digital power; 2: high performance CMOS; 3: bipolar). In all likelyhood, the CP chips will be extra that listens to the analog input. Either the input or the output are begging to be cut off. Note that Sony (and probably other sources) provide really nice service-manuals with circuit diagrams, PC-board layouts and anything you need to know. For more fun, the control processor may exchange encrypted messages with the CP-chip. But even this exercise leaves the input to it vulnerable. Now for the 10c question: why should a DAT company spend a lot of resources on the CP part to do a good job here? After all, they are fighting this restriction. I think that the time it takes a person with EE background to defeat this circuit is best measured in minutes. -- Andreas